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Print in friendly format Send this term to a friend  Driver Information Center
Also known as the DIC.

This is the display readout panel on the dash. It's above the radio for 1984-1989; above the climate controls, 1990-1996.
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Matatk How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light.
Webmaster
SW Chicago Burbs
21618 Posts
Member since:
2008/1/7 0:00



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This has been coming up recently so I wanted to have this on the site. I compiled this from various sources along with my some of my own explanations. I believe it to be correct as it is. If you have any suggestions or changes, please let me know.

If your check engine light comes on, it can be easily checked with a paperclip. You do not need an expensive scanner. The proper scanner to use is the expensive (and hard to come by) Tech 1 (or Tech 1a). Be careful with aftermarket scanners, they often will not connect or will give false data.

For 84-89 (OBDI)


Start with the car off. Locate the ALDL (assembly line diagnostic link) under the driver's side dash near your right knee. Bend the paperclip in half and insert it in the a and b terminals to "jumper" the connection. Turn the accessory power on (do not start the car). Then watch the dashboard SES light and count how many times it flashes. You should see it flash once, then pause, then flash twice, then pause. This means "12". It should do this three times which indicates the circuit is working. If you only get 12, there are no other codes. If you see additional flashes after 12, write those codes down because that is what you will be troubleshooting.

ALDL photo ALCLALDLimage.gif

Not a Corvette, but gives a good visual explanation of what a "code 12" looks like:

 photo SESAnimation.gif



1990-1993


In 1990, the interior and dash changed along with the computer system. The codes are stored in the CCM. The technique for checking codes is similar, but you jumper the pins a and g on the connector. The speedometer is used for reading the codes.

 photo speedo_display.jpg

1993 Corvette Service Manual book 1 page 8D-4

DIAGNOSIS
The Central Control Module (CCM) uses the speedometer, odometer, and the trip monitor located on the instrument cluster to display information while in the diagnostic mode.

The speedometer is used to display Diagnostic Trouble Codes (DTCs) (CCM, ABS/ARS and ECM), the odometer displays data, and the trip monitor indicates the system being tested and the test which is being performed. The buttons on the Driver Information Center (DIC) are used to send instructions to the CCM when in the diagnostic mode.

Unlike other vehicle electronic systems, such as ECM, SIR, etc., there is no specific "CCM" lamp to indicate a malfunction. A DTC-setting malfunction in any of the CCM-monitored systems is indicated by "SYS" (SYSTEM ERROR) flashing in the instrument cluster trip monitor. If a malfunction does not recur within 100 ignition cycles the CCM will automatically clear the DTC.

The "SYS" indicator will flash 3 times every 15 seconds while a current-DTC malfunction is present. An exception to the "SYS" malfunction indicator is that PASS-Key malfunctions (DTCs 51-53) will be indicated by the "SECURITY" lamp being illuminated without the "SYS" indicator flashing. If there is a Fuel Enable Data Stream (FEDs) malfunction (DTC 54), the "SECURITY" indicator and "SYS" indicator will flash together, to illustrate that the problem condition affects vehicle security.

DIAGNOSTIC MODE
To enter the diagnostic mode, ground (connect it to pin "A") pin "G" of the Data Link Connector (DLC) located under the right side of the dash, and turn the ignition switch to the "ON" position.

A = Ground
B = ECM Diagnostic
C = Ride Control Diagnostic
F = T.C.C (VIN P)
G = CCM Diagnostic
J = E&C Bus Data
K = SIR Diagnostic
L = SIR Serial Data
M = Serial Data

DLC connector -->
-------------
|F| | |C|B|A|
|G| |J|K|L|M|
-------------

- Important: If the A/C fuse is blown, the CCM will not receive IGN 3 power and will not enter diagnostic mode. This condition should also be indicated by a DCT 16 being set.

After turning the ignition "ON", the CCM will display any DTCs and the module for which they apply is an automatic DTC sequence. The CCM is module 1, the ECM is module 4, the ABS/ASR EBTCM is module 9. During the automatic display sequence, each DTC is displayed for three seconds, followed by a one second pause before the next DTC is displayed. There is a three second pause between the DTC display sequence for each module. The end of the DTC list for each module is indicated by "---" being displayed in the speedometer. If there is a communications problem between the ECM or EBTCM and the CCM, the speedometer will display "Err" when the CCM is trying to communicate with the ECM or EBTCM.

- Important: The CCM will display "Err" when attempting to display ECM DTCs for the LT5 engine. CCM display and cleaning of ECM DTCs is available only for the LT1. Use the Tech 1 for ECM DTCs on LT5.

The particular module being interrogated is indicated on the trip monitor, and the DTCs are displayed on the speedometer. The speedometer also indicates if the DCT is a current DTC (malfunction present now) or history DTC (malfunction has occurred, but is not present now) with a "C" or an "H", respectively. All ECM and EBTCM DTCs will be displayed by the CCM as history DTCs, weather they are current or history. ** reference

When all DTCs have been displayed for all modules, the trip monitor will display 1.0 and the speedometer will be blank; this indicates the CCM is in the manual mode, waiting for input from the technician. At any time during the automatic DTC display sequence, the manual mode may be entered by pressing any button on the DIC.

MANUAL MODE
The manual mode can be entered as described previously, or will automatically be entered after the automatic DTC display sequence is complete.

When manual mode is entered, the speedometer will be blank, and the trip monitor will display "1.0", indicating that module "1" (the CCM) is ready for further instructions. The buttons on the DIC are used to control other systems and options as illustrated in Figure 4 (the Driver Information Center).

The indicator "--" will be displayed on the speedometer if the end or beginning of a list of malfunction DTC’s is reached (using the "Next Value" or "Previous Value" button). The "--" will also display if no DTC's are present for the module being checked.

1994-1996

In 1994, the Corvette began transitioning from OBD1 (OBDI) to OBD2 (OBDII). It used the OBD2 connector, but with OBDI data until 1996 when it was federally mandated. Some people refer to this at OBD1.5. From what I have read, no aftermarket scanners will function correctly with the OBD1.5 system. There is a special adapter cartridge used with the Tech 1 for these years.

 photo obd2dlc.gif

Originally Posted by Casethecorvetteman

On a 94-96 you can check the codes with a paper clip as follows:

You short pin "12" to pin "4" and turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.
Finally, Module "A", the DERM (Dynamic Energy Control Module --- (the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer (big) and read the module number on the trip odometer (small).

A series of dashed lines for instance “ - - -“ indicates no more stored codes for that module.

A code showing as “C12” for the CCM module (module #1) means no codes are stored. So C12 is a good thing to see.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.

Turn the ignition off and remove the short to restore normal operation.

To clear the codes,

1. With ignition "off" ground terminal #12 of the DLC (use bent paper clip to connect pin 4 to pin 12)

2. Turn ignition "on".

3. Press trip/odo button on the DIC until 1.7 appears in the trip
monitor area of the instrument cluster.

4. Press eng/met button on the DIC & hold until "---" appears in the
speedometer area of the cluster, this will clear CCM DTC'S.


To clear PCM/ECM codes do the following:


1. Press the trip reset button on the DIC until the desired system is displayed. In this case it will be 4.0.

2. Press trip/odo button on the DIC until the desired diagnostic mode(4.7) is displayed on the trip monitor area of the cluster.

3. Press & hold the eng/met button on the DIC until "---" is
displayed in the speedometer area of the cluster, this will clear PCM codes.


To clear ABS/ASR codes do the following:

Same as above but you’re looking for “9.7” on the trip odo



CODE EXPLANATIONS



1984:

code #13: oxygen sensor
code #14: coolant sensor
code #15: coolant sensor
code #21: throttle position sensor
code #22: throttle position sensor
code #23: manifold air temp sensor
code #24: vehicle speed sensor
code #25: manifold air temp sensor
code #32: egr system
code #33: map sensor
code #34: maf sensor
code #35: idle air control
code #41: cylinder select error
code #42: electronic spark control
code #43: electronic spark control
code #44: lean exhaust
code #45: rich exhaust
code #51: PROM
code #52: fuel calpak
code #53: system over voltage
code #54: fuel pump circuit
code #55: ecm
code #62: oil temp

1985-1991

Code #12: Normal No Codes.
Code #13: Open Oxygen Sensor Circuit.
Code #14: Coolant Sensor Circuit Low.
Code #15: Coolant Sensor Circuit High.
Code #21: Throttle Position Sensor High.
Code #22: Throttle Position Sensor Low.
Code #23: Manifold Air Temperature Circuit High.
Code #24: Vehicle Speed Sensor.
Code #25: Manifold Air Temperature Circuit Low.
Code #32: EGR System Failure.
Code #33: Mass Air Flow Sensor High.
Code #34: Mass Air Flow Sensor Low.
Code #36: Mas Air Flow Sensor Burn-Off Function Fault.
Code #41: Cylinder Select Error.
Code #42: Electronic Spark Timing.
Code #43: Electronic Spark Control.
Code #44: Lean Exhaust indication.
Code #45: Rich Exhaust Indication.
Code #46: Vehicle Anti Theft Fault.
Code #51: Faulty Mem-Cal.
Code #52: Fuel Calpak Missing.
Code #52(1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
Code #53: System Over Voltage.
Code #54: Fuel Pump Circuit Low Voltage.
Code #55: Defective ECM.
Code #62: Engine Oil Temperature Sensor Circuit High

1992-1993


Code #12: Normal No Codes.
Code #13: Left Oxygen Sensor Circuit.
Code #14: Coolant Temperature Sensor Circuit High.
Code #15: Coolant Temperature Sensor Circuit Low.
Code #16: Opti-Spark Ignition Timing System.( Low Pulse)
Code #21: Throttle Position Sensor Circuit High.
Code #22: Throttle Position Sensor Circuit Low.
Code #23: Intake Air Temperature Sensor Circuit Low.
Code #24: Vehicle Speed Sensor Circuit.
Code #25: Intake Temperature Sensor Circuit High.
Code #26: Quad-Driver Module #1 Circuit.
Code #27: Quad-Driver Module #2 Circuit.
Code #28: Quad-Driver Module #3 Circuit.
Code #32: Exhaust Gas Recirclation Circuit.
Code #33: Manifold Absolute Pressure Sensor Circuit Low.
Code #34: Manifold Absolute Pressure Sensor Circuit High.
Code #36: Opti-Spark Ignition Timing System. (High Resolution Pulse.)
Code #41: Electronic Spark Timing Circuit Open.
Code #42: Electronic Spark Timing Circuit Grounded.
Code# 43: Electronic Spark Control Circuit.
Code #44: Left Oxygen Sensor Circuit Lean.
Code #45: Left Oxygen Sensor Circuit Rich.
Code #51: Mem-Cal Error.
Code #52: Engine Oil Temperature Sensor Circuit Low.
Code #53: System Voltage.
Code #55: Fuel Lean Monitor.
Code #56: Vacuum Sensor Circuit.
Code #61: Secondary Port Throttle Valve System.
Code #62: Engine Oil Temperature Sensor Circuit High.
Code #63: Right Oxygen Sensor Circuit Open.
Code #64: Right Oxygen Sensor Circuit Lean.
Code #65: Right Oxygen Sensor Circuit Rich.
Code #66: A/C Pressure Sensor Circuit Open.
Code #67: A/C Pressure Sensor Circuit. (Sensor or A/C Clutch Circuit Problem)
Code #68: A/C Relay Circuit Shorted.
Code #69: A/C Clutch Circuit.
Code #72: Gear Selector Switch Circuit.

1994-1996 (1992-1996)

1992-1996 (LT-1 VIN P)

DTC Codes 72-99 Pertain to 1994-1996 (LT-1 VIN P)

DTC 11 - Malfunction Indicator Lamp (MIL) Circuit
DTC 13 - Bank 1Left Front) Heated Oxygen} Oxygen Sensor (H02S) #1 Circuit (Open Circuit)
DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit (Signal Voltage Low, High Temperature Indicated)
DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit (Signal Voltage High, Low Temperature Indicated)
DTC 16 - Distributor Ignition System (Low Resolution Pulse)
DTC 18 – Injector Circuit(s)
DTC 21 - Throttle Position (TP) Sensor Circuit (Signal Voltage High)
DTC 22 - Throttle Position (TP) Sensor Circuit (Signal Voltage Low)
DTC 23 - Intake Air Temperature (IAT) Sensor Circuit (Signal Voltage High, Low Temperature Indicated)
DTC 24 - Vehicle Speed Sensor (VSS) Circuit
DTC 25 - Intake Air Temperature (IAT) Sensor Circuit (Signal Voltage Low, High Temperature Indicated)
DTC 26 - Evaporative Emission (EVAP) Canister Purge Solenoid Valve Circuit
DTC 27 - Exhaust Gas Recirculation (EGR) Vacuum Control Signal Solenoid Valve Circuit
DTC 28 - Transmission Range (TA) Pressure Switch Assembly Fault
DTC 29 - Secondary Air Injection (AIR) Pump Circuit
DTC 32 - Exhaust Gas Recirculation (EGR)
DTC 33 - Manifold Absolute Pressure (MAP) Sensor Circuit (Signal Voltage High – Low Vacuum)
DTC 34 - Manifold Absolute Pressure (MAP) Sensor Circuit (Signal Voltage Low – High Vacuum)
DTC 36 - Distributor Ignition System (Faulty High Resolution Pulse or Extra Low Resolution Pulse Detected)
DTC 37 - Brake Switch Stuck “ON
DTC 38 - Brake Switch Stuck “OFF”
DTC 41 - Ignition Control (IC) Circuit (Open Circuit)
DTC 42 - Ignition Control (IC) Circuit (Shorted or Grounded Circuit)
DTC 43 - Knock Sensor (KS) Circuit
DTC 44 - Bank 1 (Left Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Lean Exhaust Indicated)
DTC 45 - Bank 1 (Left Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Rich Exhaust Indicated)
DTC 47 - Knock Sensor (KS) Circuit or Module Missing
DTC 48 - Mass Air Flow (MAF) Sensor Circuit
DTC 50 - System Voltage Low
DTC 51 - EEPROM Programming Error
DTC 52 - Engine Oil Temperature Sensor Circuit (Signal Voltage High, Low Temperature Indicated)
DTC 53 - System Voltage High
DTC 55 - Fuel Lean Monitor
DTC 58 - Transmission Fluid Temperature (TFT) Sensor Circuit Low (High Temperature Indicated)
DTC 59 - Transmission Fluid Temperature (TFT) Sensor Circuit High (Low Temperature Indicated)
DTC 62 - Engine Oil Temperature Sensor Circuit (Signal Voltage Low, High Temperature Indicated)
DTC 63 - Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Open Circuit)
DTC 64 - Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Lean Exhaust Indicated)
DTC 65 - Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #t Circuit (Rich Exhaust Indicated)
DTC 66 - A/C Refrigerant Pressure Sensor Circuit (Open or Shorted)
DTC 67 - A/C Refrigerant Pressure Sensor Circuit (Pressure Sensor or A/C Clutch Circuit Problem)
DTC 68 - A/C Relay Circuit (Shorted Circuit)
DTC 69 - A/C Clutch Circuit
DTC 70 - A/C Clutch Relay Driver Circuit
DTC 72 - Vehicle Speed Sensor Loss
DTC 73 - Pressure Control Solenoid (PCS) Circuit (Current Error)
DTC 74 - Traction Control System (TCS) Circuit Low
DTC 75 - Transmission System Voltage Low
DTC 77 - Fan Control PCM Terminal “All”
DTC 78 - Fan Control PCM Terminal “Al0″
DTC 79 - Transmission Fluid Over-temp
DTC 81 - Transmission .2-3 Shift Solenoid Circuit
DTC 82 - Transmission 1-2 Shift Solenoid Circuit
DTC 83 - TCC PWM Solenoid Circuit Fault
DTC 84 - 3-2 Control Solenoid Circuit (Automatic Transmission)
DTC 84 - 2nd and 3rd Gear Block-out Relay Control Circuit (Manual Transmission)
DTC 85 - Transmission TCC Stuck “ON”
DTC 90 - Transmission TCC Solenoid Circuit
DTC 91 - One to Four Upshift Lamp (Manual Transmission)
DTC 97 - VSS Output Circuit
DTC 99 - Tach Output Circuit
DTC P0116 – Engine Coolant Temperature (ECT) Circuit Range/Performance Problem
DTC P0117 – Engine Coolant Temperature (ECT) Circuit Low Input
DTC P0118 – Engine Coolant Temperature (ECT) Circuit High input
DTC P0131 – Bank 1 HO2S #1 Circuit Low Voltage (Lean
DTC P0132 – Bank 1 HO2S #1 Circuit High Voltage (Rich)
DTC P0133 – Bank 1 HO2S #1 Circuit Slow Response
DTC P0134 – Bank 1 HO2S #1 Circuit No Activity Detected
DTC P0135 – Bank 1 HO2S #1 Heater Circuit
DTC P0151 – Bank 2 HO2S #1 Circuit Low Voltage (Lean)
DTC P0152 – Bank 2 HO2S #1 Circuit High Voltage (Rich)
DTC P0153 – Bank 2 HO2S #1 Circuit Slow Response
DTC P0154 – Bank 2 HO2S #1 Circuit No Activity Detected
DTC P0155 – Bank 2 HO2S #1 Heater Circuit Malfunction
DTC P0158 – Bank 2 HO2S #2 Circuit High Voltage
DTC P0160 – Bank 2 HO2S #2 Circuit No Activity Detected
DTC P0161 – Bank 2 HO2S #2 Heater Circuit Malfunction
DTC P0171 – Bank 1 Fuel Trim System Too Lean
DTC P0172 – Bank 1 Fuel Trim System Too Rich (1 of 2)
DTC P0174 – Bank 2 Fuel Trim System Too Lean
DTC P0175 – Bank 2 Fuel Trim System Too Rich (1 of 2)
DTC PO420 – Bank 2 Catalyst System – Low Oxygen Storage Capacity Indicated
DTC P1114 – Engine Coolant Temperature (ECT) Circuit (intermittent Low Input Voltage)
DTC P1115 – Engine Coolant Temperature (ECT) Circuit (Intermittent High Input Voltage)
DTC P1133 – Bank 1 HO2S #1 Circuit Not Enough Switches
DTC P1153 – Bank 2 HO2S #1 Circuit Not Enough Switches
DTC P1158 – Bank 2 HO2S #2 Shifted Rich

1994-1995 LT5/ZR-1 Trouble codes

Due to federal regulations implementing uniform trouble codes throughout the automotive industry LT5/ZR-1 Corvettes used many of the same 1994 and up codes with the exception of the codes listed below. (These trouble codes may be in addition to the possible codes above or different meaning)

DTC 31 Camshaft Position Sensor Circuit
DTC 41 Cylinder Select Error (Faulty or Incorrect PROM)
DTC 54 Fuel Pump Circuit (Low Voltage)
DTC 56 Secondary Air Inlet Valve Actuator Vacuum Sensor Circuit (Signal Voltage High “High Vacuum or Signal Voltage Low” (Low Vacuum)
DTC 61 Secondary Air Inlet Valve System
DTC 66 Engine Power Mode Switch Circuit (Signal Voltage High or Signal Voltage Low)

4.7 clear ECM fault codes

Press the TRIP RESET button until 4.0 is displayed in the module number area. Then press the TRIP/ODO button until 4.7 is displayed in the module number area. Press and hold the ENG/MET button until “—“ is displayed. This will clear any ECM codes. After “—“ is displayed turn the key off, wait ten seconds turn the key back on and check for any ECM codes.

ABS/ASR EBTCM

Press the TRIP RESET button until 9.0 is displayed in the module number area. Press the TRIP/ODO button until “9.7″ is displayed in the module number area. Press and hold the ENG/MET button until “—“ is displayed. This will clear any ABS/ASR codes. after “—“ is displayed, turn the key off, wait ten seconds, turn the key back on and check for any ABS/ASR codes.

Hope this helps.

Matthew
Posted on: 2014/10/13 13:19
_________________

1989 Corvette...custom 383 stroker, superrammed and cammed, built trans with PeteK 2800 stall. Mustang dyno results: 336 rwhp / 419 rwtq.
Transfer the post to other applications Transfer

Matatk Re: How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light.
Webmaster
SW Chicago Burbs
21618 Posts
Member since:
2008/1/7 0:00



Offline
(copied, not necessarily Corvette specific)

CODE 12
Trouble Code 12 is a special-case code that is not logged into the ECM's Non-Volatile Memory (NVM) when detected. When the ECM detects no ignition reference pulses from the ignition module when the ignition is in the 'ON' position, it illuminates the Check Engine Lamp (CEL), but does not log this code as it would other codes.
Code 12 is used on most systems when in the Diagnostic mode (ALDL Terminal B grounded, key-on/engine-off) to signal the beginning or end of a so-called 'diagnostic sequence', when the ECM annunciates each stored code in the ECM's NVM on the dash CEL.
When in this mode, the ECM will begin by flashing code 12 on the CEL 3 times. This indicates the beginning of a diagnostic sequence. It will then flash any codes stored in NVM 3 times each before proceeding to the next code. When all stored codes are finished, the ECM will again flash code 12 to indicate the end of the diagnostic sequence. The cycle will continue as long as the ECM is in Diagnostic Mode.

CODE 13
Trouble Code 13 indicates that the exhaust stream oxygen-content sensor (O2 sensor) is not responding as expected. When cold, the sensor is 'biased' by the ECM to about 450 millivolts. Before it warms to at least 600 deg F (315 deg C) it acts as an open circuit and when the ECM reads it, it reads the 450 mV bias. The ECM expects the sensor to warm in a short period of time and begin sending its own voltages. The general conditions for this code getting set are:
? engine running at least 2 minutes
? coolant temperature at least 50 deg C (122 deg F)
? O2 voltage not fluctuating (i.e steady between 350 and 550 mV)
? TPS signal above idle
? all above conditions met for 60 seconds

Typical causes may include:
1. Defective or degraded O2 sensor
2. Deposit-contaminated O2 sensor (running leaded fuel, RTV silicone deposits etc)
3. Corroded/defective O2 sensor connection
4. Defective sensor ground circuit
5. Defective connection at ECM
6. Defective ECM
NOTE: If codes 21 and/or 22 are also present cause '4' above should be checked first.

CODE 14
Trouble Code 14 indicates that the Coolant Temperature Sensor (CTS) is reporting abnormally high readings. CTS is used to control fuel mixture, timing, idle speed, TCC and EGR operations among others. The thermistor used has a high-resistance when cold, lowering as the coolant warms.
Code 14 will set if:
? temperature reported is > 270 deg F (135 deg C)
? conditions above are present for more than 20 seconds

Typical causes may include:
1. Severe engine overheating
2. Defective Coolant Temperature Sensor
3. Short circuit in CTS-ECM harness
4. Defective ECM

CODE 15
Trouble Code 15 indicates that the Coolant Temperature Sensor (CTS) is reporting abnormally low readings. CTS is used to control fuel mixture, timing, idle speed, TCC and EGR operation, among others. The thermistor used has a high-resistance when cold, lowering as the coolant warms.
Code 15 will set if:
- temperature reported is < -37.30 deg F (-38.5 deg C)

Typical causes may include:
1. Open circuit in CTS-ECM harness
2. Defective Coolant Temperature Sensor
3. Open sensor ground circuit
4. Defective ECM

CODE 21
Trouble Code 21 indicates that the Throttle Position Sensor (TPS) is reading abnormally high. TPS volts should be close to 0.42 V at closed throttle and rise smoothly in about 0.02 volt increments to a maximum reading of about 4.85 volts at WOT.
Code 21 will set if:
? Engine is running
? TPS signal voltage is greater than 4.3 volts
? No Code 33 or Code 34
? Air Flow is less than 17 gm/sec.
? All conditions met for 1.25 seconds

Typical causes for this code include:
1. Defective TPS
2. Short circuit in the TPS harness to +5 volt reference
3. Open sensor ground circuit
4. Defective ECM
NOTE: Presence of codes 33 and/or 34 may indicate that the MAP sensor is defective and is reading less than expected. This may cause the above set-conditions to be met falsely and this code to be set.

CODE 22
Trouble Code 22 indicates that the Throttle Position Sensor (TPS) is reading abnormally low. TPS volts should be close to 0.42 V at closed throttle and rise smoothly in about 0.02 volt increments to a maximum reading of about 4.85 volts at WOT.
Code 22 will set if:
? Engine Running
? TPS reading < 0.25 volts for 3 seconds

Typical causes for this code include:
1. Circuit Open or Shorted to Ground
2. Faulty Connection
3. Faulty TPS
4. Defective ECM
TPS cannot be adjusted, the TPS has an auto zeroing feature.

CODE 23
Trouble Code 23 indicates that the Manifold Air Temperature (MAT) sensor or Intake Air Temperature (IAT) is reading lower than expected. When the air is cold, the thermistor has a high resistance, which falls as the air charge warms. Low readings thus indicate possible open circuits in MAT circuit.
Code 23 will set if:
? MAT reading is < -31 deg F (-35 deg C)
? Time since engine start is 4 minutes or longer.
? Vehicle speed less than 1 mph
? Start-up coolant temperature is less than or equal to -35.5 C (31.9 F).
? All conditions met for 10 sec.

Typical causes for this code include:
1. Defective MAT or IAT sensor
2. Open sensor ground circuit
3. Dirty or corroded connection(s) at MAT/IAT and/or ECM
4. Open circuit between the ECM and the MAT/IAT sensor
5. Defective ECM

CODE 24
Trouble Code 24 indicates that the Vehicle Speed Sensor (VSS) is not sending the expected (based on other system parameters like LV8, TPS, RPM etc.) signal to the ECM.
Code 24 will be set if vehicle speed equals zero 0 mph when:
? VSS indicates less than 2mph.
? MAP is less than 30 kPa.
? Engine speed is between 2200 and 4400 RPM
? TPS is less than 2%.
? Not in Park or Neutral
? No Code 21, 22, 33, or 34.
? All conditions met for 3 seconds

If the code was logged when the vehicle was in motion, the following should be checked:
1. VSS circuit open, shorted to ground, shorted together
2. Faulty Connections
3. Defective VSS
4. Defective ECM
5. A faulty or misadjusted Park/Neutral (P/N) switch can result in false Code 24.

CODE 25
Trouble Code 25 indicates that the Manifold Air Temperature (MAT) or Intake Air Temperature (IAT) sensor is reading higher than expected. When the air is cold, the thermistor has a high resistance, which falls as the air charge warms. High readings thus indicate possible short circuits in MAT circuit.
Code 25 will set if:
? MAT/IAT reading is > 293 deg F (135 deg C) for .2 seconds
? vehicle speed is greater than 1 MPH

Typical causes for this code include:
1. Defective MAT/IAT sensor
2. MAT/IAT signal shorted to ground or to sensor ground
3. Defective ECM

CODE 26
Trouble Code 26 indicates that the quad-driver is malfunctioning.
QDM symptoms:
? Cooling fan(s) inoperative
? Poor drivability due to 100% canister purge.
? Coolant light "ON" all the time, "OFF" during bulb check.
? EGR inoperative - Code 32.
? TCC inoperative

This problem can be caused by:
1. Short to 12 volts on the control circuit by a shorted component.
2. Faulty ECM.

CODE 32
Trouble Code 32 indicates that the Exhaust Gas Recirculation (EGR) system has detected a fault. There are two types, the older integrated electronic EGR contains a voltage regulator which converts the ECM signal to provide different amounts of EGR flow by regulating the current to the solenoid. The ECM controls EGR flow with a pulse width modulated signal (turns "ON" and "OFF" many times a second) based on airflow, TPS, and RPM. This system also contains a pintle position sensor which works similar to a TPS sensor, and as EGR flow is increased, the sensor output also increases. The other type is a digital 3-level EGR used in newer engines. Code 32 will get set when:
? (Integrated EGR) Coolant temperature above the specified amount, EGR should be on.
? (Integrated EGR) EGR pintle position does not match duty cycle.
? (Digital EGR) Failure of EGR system.

Possible causes include:
1. Faulty EGR valve-to-ECM connection
2. Plugged EGR passages and/or sticking EGR valve
3. Defective EGR valve
4. Defective ECM
Check the shop manual for details on vehicle specific EGR valve applications.

CODE 33
Trouble Code 33 indicates that the Manifold Absolute Pressure (MAP) sensor is detecting unusually low vacuum in the manifold. Code 33 will get set when:
? No Code 21 or Code 22.
? Engine running.
? Manifold pressure greater than 74 kPa (A/C "OFF") 83.4 kPa (A/C "ON.")
? Throttle angle less than 2%.
? Conditions met for 4.8 seconds.

Possible causes include:
1. Faulty MAP-to-ECM connection
2. Plugged or leaking sensor vacuum hose
3. Defective MAP sensor
4. Defective ECM
Check the shop manual for details on vehicle specific MAP sensor applications.

CODE 34
Trouble Code 34 indicates that the Manifold Absolute Pressure (MAP) sensor is detecting unusually high vacuum in the manifold. Code 34 will get set when:
? Engine RPM less than 700.
? Manifold pressure reading less than 13 kPa.
? Conditions met for .22 second.

OR

? Engine RPM greater than 700.
? Throttle angle over 20%.
? Manifold pressure less than 13 kPa.
? Conditions met for .22 second.

Possible causes include:
1. Faulty MAP-to-ECM connection
2. Defective MAP sensor
3. Defective ECM
Check the shop manual for details on vehicle specific MAP sensor applications.

CODE 35
Trouble Code 35 indicates a problem with the Idle Speed Control (ISC) circuit. It will be set when the closed throttle engine speed is 200 RPM above or below the desired (commanded) idle speed for 50 seconds. Possible causes include:
1. Vacuum Leak (High Idle) - Also check for binding of throttle blade or linkage.
2. System too lean (High Air/Fuel Ratio) - The idle speed may be too high or too low. Check for low regulated fuel pressure, water in the fuel, or a restricted injector.
3. System too rich (Low Air/Fuel Ratio) - The idle speed will be too low. May exhibit black smoke in exhaust. Check for high fuel pressure, leaking or sticking injector.
4. Foreign material in throttle body.
5. Faulty IAC Valve electrical connections.
6. Faulty PCV valve.
7. Faulty IAC.
8. Faulty ECM.

CODE 41
Trouble Code 41 indicates an incorrect MEM-CAL has been installed or it is faulty and it must be replaced.
Possible causes include:
1. Faulty connection due to MEM-CAL not locked in place.
2. Incorrect MEM-CAL installed.
3. Faulty MEM-CAL.

CODE 42
Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system. During cranking, the timing is controlled by the ignition module and the ECM grounds the EST line. It expects to see no activity on this line at this time. When the ECM enters EST mode, it applies +5 volts to the BYPASS line and expects to see voltage variations on the EST line.
Reasons for the ECM to set Code 42:
? System in BYPASS mode (i.e. EST line supposedly grounded) but activity sensed on EST line
? System in EST mode (i.e. BYPASS line driven with +5 volts) but no activity seen on the EST line

Possible causes include:
1. BYPASS line is open or grounded
2. EST line is open or grounded
3. Poor connections between ignition module and ECM
4. Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise
5. Faulty or incorrect ignition module
6. Faulty ECM

CODE 43
Trouble Code 43 indicates that there may be a malfunction in the Electronic Spark Control (ESC) circuit. ESC is used to sense spark knock (pinging) and retard the timing to eliminate it. The knock sensor is located at the rear of the engine block. The ECM will retard the timing by as much as 20 degrees in 1 degree increments. A loss of knock sensor signal or loss of ground at the ESC module will cause the signal at the ECM to remain high. The ECM will act as if no knock is present, and
may possibly result in engine damage, due to detonation.
Code 43 is set when:
? Voltage at Knock Sensor is above 4.8 volts or below .64 volts.
? Either condition is met for about 10 seconds.

Possible causes:
1. Open or shorted knock sensor
2. Loose knock sensor
3. Excessive mechanical noise within engine
4. Improper or incorrectly installed MEM-CAL in the ECM or defective ECM
5. Intermittent open in the EST line to the ignition module

CODE 44
Trouble Code 44 indicates that the O2 sensor is showing a persistently high exhaust oxygen content (lean), despite the efforts of the ECM to increase injector on-time (thus increasing fuel delivered). Integrator and BLM numbers may indicate > 128 by a substantial margin.
Code 44 is set when:
? O2 sensor voltage remains below .2 volt for 60 or more seconds
? System is operating in "Closed Loop."
? No Code 33 or Code 34

Possible causes include:
1. O2 sensor defective or lead shorted (A plugged catalectic converter will render the O2 sensor defective)
2. Lean injectors (dirty or blocked)
3. Water in fuel
4. Exhaust leaks upstream of O2 sensor
5. Fuel pressure too low
Note: Presence of Code(s) 33 and/or 34 may indicate MAP problem. This should be the first suspect in the case of a Code 44 being set.

CODE 45
Trouble Code 45 indicates that the O2 sensor is showing a persistently low exhaust oxygen content (rich), despite the efforts of the ECM to decrease injector on-time (thus decreasing fuel delivered). Integrator and BLM numbers may indicate < 128 by a substantial margin.
Code 45 is set when:
? O2 sensor voltage remains above .7 volt for 50 seconds
? engine has been running for 1 minute or more
? throttle is between 3 and 45 percent open
? system is running "Closed Loop"

Possible causes include:
1. O2 sensor defective or contaminated (A plugged catalectic converter will render the O2 sensor defective)
2. Leaking fuel injectors
3. Fuel pressure too high
4. EMI interference from poor plug wires
5. Evaporative Emission system defect
6. TPS and/or EGR problem
Note: Presence of Code(s) 33 and/or 34 may indicate MAP problem. This should be the first suspect in the case of a Code 45 being set.

CODE 51
Trouble Code 51 indicates that the ECM sensed a fault in the MEM-CAL. On power-up, the ECM does a checksum of the MEM-CAL to ensure the MEM-CAL integrity is good. If the calculated sum does not match the sum in the MEM-CAL, the ECM will hardcode 51 and enter Back-Up mode, since the ECM cannot know where in the MEM-CAL the fault lies.
Code 51 is set when:
? the actual MEM-CAL checksum does not match the value in the MEM-CAL
Possible causes include:
1. Incorrectly installed MEM-CAL module
2. Defective MEM-CAL module
3. Defective ECM

CODE 52
Trouble Code 52 indicates that the ECM sensed a fault in the CALPACK. The CALPACK is a module separate from the PROM that contains preset calibrations used by the system in the limp-home mode. The ECM checks for its presence at power up.
Code 52 gets set when:
? the ECM does not sense the CALPACK
Possible causes include:
1. Incorrectly installed CALPACK module
2. Incorrect CALPACK module for this vehicle
3. Defective or incorrectly inserted PROM
4. Defective ECM

CODE 53
This code will be set when the ignition is "ON", and the engine RPM is greater than 800 and the ECM is seeing a ignition fuel reference voltage of more than 17.1 volts. During the time of this failure, all ECM outputs will be disengaged.
Possible causes include:
1. Faulty generator.
2. Faulty ECM.

CODE 54
Trouble Code 54 indicates a low voltage at the fuel pump. If the voltage at terminal "A20" is less than 4 volts for .4 seconds since the last reference pulse was received, the code will be set.
Possible causes include:
1. Faulty fuel pump relay.
2. Faulty connection at ECM.
3. Faulty oil pressure switch.
4. Faulty ECM.

CODE 55
Trouble Code 55 indicates that the Analog- to-Digital (A/D) converter in the ECM timed out. The ECM checks this by initiating a conversion and timing how long it takes to complete. If the converter, for whatever reason, fails to signal the End-Of-Conversion (EOC) before a timeout counter runs down, the ECM assumes it is bad and sets this code.
Possible causes for Code 55 are limited to:
1. Defective or incorrectly inserted MEM-CAL
2. Defective ECM
If replacing the ECM, be sure to transfer both the PROM and the CALPACK from the old unit. If the old-ECM also indicated PROM failure (Code 51) or a bad CALPACK (Code 52), be sure to verify these components are fully operational in the new unit. If they are not, they too will have to be replaced.

CODE 61
Trouble Code 61 indicates that the ECM has determined the oxygen sensor is contaminated or degraded, because the voltage change time is slow or sluggish.
Possible causes:
1. Contaminated Oxygen sensor.
2. Oxygen sensor needs replacement.


CODE 66
Trouble Code 66 indicates that A/C pressure sensor has determined that the A/C refrigerant system pressure is either too low (0 psi, .1 volt at sensor) or too high (450 PSI, 4.6 volts at sensor) for 5 seconds or more. If this code is present, the A/C compressor is disabled by the ECM.
Possible causes:
1. A/C system pressure is above or below calibrated values.
2. Faulty A/C Pressure Sensor or wiring.
3. Faulty ECM.
Posted on: 2014/10/13 13:20
_________________

1989 Corvette...custom 383 stroker, superrammed and cammed, built trans with PeteK 2800 stall. Mustang dyno results: 336 rwhp / 419 rwtq.
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istter1 Re: How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light.
Elite Guru
Bakersfield Ca
2249 Posts
Member since:
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Cool
Posted on: 2014/10/13 13:25
_________________
Only I can change my life. No one can do it for me.
Carol Burnett
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Schrade Re: How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light.
Elite Guru
eastern NC / e-i-e-i-o
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Sticky it UP TOP.




Tried the above text twice in 2 different browser pages - following is the server response:

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An appropriate representation of the requested resource /modules/newbb/post.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.


Tried the 3rd time, 'quoting' isitter1, with success, then edited out the quote.

??? Matt?
Posted on: 2014/10/13 18:06
_________________
LT5, Marc Haibeck ECM module, AUTOMATIC!!!

Resized Image
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Matatk Re: How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light.
Webmaster
SW Chicago Burbs
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Quote:

Schrade wrote:

Sticky it UP TOP.




Tried the above text twice in 2 different browser pages - following is the server response:

Not Acceptable

An appropriate representation of the requested resource /modules/newbb/post.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.


Tried the 3rd time, 'quoting' isitter1, with success, then edited out the quote.

??? Matt?


There is some glitch between the site software and server. Sometimes it gives that error and you have to "quote" the post above to get it to work. Hopefully it will be solved with the next upgrade.
Posted on: 2014/10/13 18:32
_________________

1989 Corvette...custom 383 stroker, superrammed and cammed, built trans with PeteK 2800 stall. Mustang dyno results: 336 rwhp / 419 rwtq.
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BrianCunningham Re: How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light.
Senior Guru
Boston, MA for the most part :)
7759 Posts
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great guru resourse
Posted on: 2014/10/13 19:23
_________________
Polo Green 95 LT1 6-spd http://mysite.verizon.net/vzevcp74/
383 LT1/Vortech Supercharger/AFR heads/Rod end suspension/Penske-Hardbar dual rate coilovers/Wilwood 6pot brakes
NCCC Governor: http://BayStateCorvetteClub.com
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