| How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light. |
Subject: How to check diagnostic trouble codes (DTCs) or diagnose service engine soon (SES) light. by Matatk on 2014/10/13 13:19:25 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.  Not a Corvette, but gives a good visual explanation of what a "code 12" looks like:  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.  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.  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 |
