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This is the manual transmission from 1984-1988.

It’s a Borg-Warner Super T-10 with a planetary overdrive attached to the tail shaft housing.
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Woodstock 86-89 Digital Instrument Cluster "OD" light
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Hi Gurus,
for an 88 automatic I wrote an 89 automatic Eprom. Never had a problem with 86, 87 and 89 Vettes. In this 88 the "OD" light comes on, which has never been seen before.
What causes the "OD" to come on in the first place? I this a sign for trouble or some sort of service light?
With the original 88 Eprom the light stays off, with the 89 Eprom it comes on right away, even without starting the engine.

I don't really know what to look for in the Eprom hack, without even understanding what causes the light to come on.

Here's a pic:

Attach file:



jpg  cluster.jpg (16.34 KB)
1024_50c36f0f899f7.jpg 343X399 px
Posted on: 2012/12/8 16:50
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Matatk Re: 86-89 Digital Instrument Cluster "OD" light
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I don't remember the 89 having the OD portion of the LCD. I will have to look later. That might be why. There is something in the code that is missing?
Posted on: 2012/12/8 17:28
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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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If you don't see it in your 89, it could be an indicator light for the 4+3 manual transmissions only. 89 started with the 6 speed manual transmission, no more OD light needed.

Any 4+3 drivers around here? Would be good to know for sure.

Posted on: 2012/12/8 18:02
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Matatk Re: 86-89 Digital Instrument Cluster "OD" light
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I had an old post that had pictures of all the years LCDs on it. I looked for 20 minutes and couldn't find it.
Posted on: 2012/12/8 19:11
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Matatk Re: 86-89 Digital Instrument Cluster "OD" light
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Aha! Found it:

http://www.corvetteguruforum.com/modu ... t_id=90869#forumpost90869

87-88 had the OD light, the other years did not.

84
Resized Image

85
Resized Image

86
Resized Image

87-88
Resized Image

89
Resized Image

Matthew

Posted on: 2012/12/8 19:28
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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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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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Thanks Matthew, that's some great info.

Now I just need to know, what turns the light on???

Another thing that puzzles me, why this 88 and not the other 87s and 88s I chiped.
Posted on: 2012/12/8 20:53
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bogus Re: 86-89 Digital Instrument Cluster "OD" light
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I would expect it is turned on either by an expectation or by the ECU.

If the ECU thinks it's in either 4th (A4) or something to that effect, it sends the instruction.

Posted on: 2012/12/8 21:29
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CentralCoaster Re: 86-89 Digital Instrument Cluster "OD" light
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From the pics of all years I would think that light is only activated on the 86-88 4+3 cars and 89 ZF6. I mean why would they bug you if driving an automatic?

The 84-85 4+3 have an overdrive light on the DIC panel, so unless GM moved it at some point that OD indicator seems redundant for a 4+3. You'd think if that little OD indicator was used by the automatics they would have kept it in 89.

The 4+3 has gear switches on the side of the 4 speed that tell the ECM what gear the car is in. I have to assume the automatic wiring harness and program would ignore all those inputs though.

Perhaps the dash in there isn't original and came from a 4+3 car, and that input is being tripped by some other signal or is grounded due to the auto harness being different? I have read that there were other dashes for cruise vs non-cruise cars so I wouldn't put it past them.

A possible way out is remove the dash and find the wire the ECM sends that signal on. If the car doesn't think it knows which gear your in it should stop hassling you. I don't have the electrical manual for 86+ though so I can't help.

Just thinking out loud.
Posted on: 2012/12/8 21:37
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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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Searching the WWW I found some info, the "OD" is a 4+3 only thing. The "OD" is like a control lamp, showing whether OD has been manually engaged or not.
Some guys on the dark site have encountered the same problem with burning eproms. Of course that damn place never offers a solution, what a waste of time.
Posted on: 2012/12/8 21:43
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CentralCoaster Re: 86-89 Digital Instrument Cluster "OD" light
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If it's like my 85 (with OD on DIC) the 4+3 ecm take a few different inputs to determine whether to activate overdrive, and the ecm directly controls that light. The shift light would have to be the same way based on gear switch inputs. So fake the inputs or disconnect the ECM outputs. They don't influence anything else.
Posted on: 2012/12/8 21:45
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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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Thanks CC!
Taking the ECM line out is a good idea. My idea would be a wrong A4 OD relay, sending out a not needed signal to the cluster. That would at least explain, why some are affected and others not.

I'll have to read the hack and see, if I can just turn a switch in the eprom to eliminate this altogether.

At least now, thanks to the Gurus, I know what I am dealing with. I had no clue, when the owner was talking about a "D" showing up permanently.

Thanks again guys!!!
Posted on: 2012/12/8 22:06
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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I suspect that the OD indicator in the 87-88 specific cluster is controlled via serial data rather than a hardwired pin.

Edit:
Got abit ahead of myself. Same idea, different bit. Must be in the 160 baud data stream. TCC bit 5 seems to fit the bill.

$32B data:
LC7CD FDB $0037 ; 55 MCU INPUT STATUS WORD
;
; Bit 0 = PARK/NEUTRAL MODE
; 1 = NOT IN THIRD GEAR
; 2 = OVERDRIVE REQUEST
; 3 = EXCESSIVE POWER STEER PRES. , CLUTCH ANTICIPTE
; 4 = EGR DIAGNOSTIC SWITCH CLOSED
; 5 = TCC LOCKED
; 6 = FAN REQUEST BIT
; 7 = 0= A/C REQUEST
;---------------------------------

Equivalent $6E data:

FDB $0038 ; 18. MCU STATUS FLG
; b0 1 = IN PARK/NEUTRAL
; b1 1 = NOT IN THIRD GEAR
; b2 1 = OVERDRIVE REQUEST
; b3 1 = EXCESSIVE POWER STEERING PRESSURE
; b4 1 = EGR DIAGNOSTIC SWITCH CLOSED
; b5 not used - OMITTED FROM S/W (1 = TCC LOCKED)
; b6 1 = FAN REQUEST BIT
; b7 0 = A/C REQUEST
;---------------------------------

Note: When I run a $6E bin in my 88, I see that bit 5 is always set when scanning. Scanning also interferes with the OD indicator, so it would need to be tested with and without scanning to confirm that the lamp and bit are related to each other.

Need to find where bit 5 is set in $6E and prevent or force it to be cleared. Will look into later.

Then you need to determine if there are any adverse effects.

I've always wanted to get to the bottom of this issue, so I may test it myself, if I get around to it.


Posted on: 2012/12/12 20:51
Edited by tequilaboy on 2012/12/12 21:31:38
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CentralCoaster Re: 86-89 Digital Instrument Cluster "OD" light
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I'm looking at the 86 ECM wiring right now... looks like you are right.

The ECM connects to the dash for serial data and speedo. Everything else is fed from other systems.

The ECM via the overdrive relay, sends the OD command to ALDL pin F, but not the cluster. Also, it does not receive any inputs from the gear switches. So all the determining of when to trigger those dash lights must be through the serial data, and calculated based on speed and rpm. This makes sense as they got rid of those switches through the years. In 85, the first gear switch did communicate with the ECM.
Posted on: 2012/12/12 21:32
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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I think I found an opportune place to clear bit 5:

By changing the ANDA #$F7 below to ANDA #$D7 at address CB5E, this should clear both bit 3 and bit 5. Only needs to execute once. Bit 5 should never be set by code.

I'll give it a shot and see what happens.

Excerpt from $6E source hac:

;----------------------
; CK AFR MODE WD
;
;----------------------
CB47: LDX #$C014 ; INDEX AFR MODE WD'S
CB4A: BRSET 2,X,#$04,LCB54 ; BR IF b2, MW3

CB4E: BRCLR 0,X,#$04,LCB54 ; BR IF NOT b2, ANALOG MAF IN USE
; ... else
CB52: EORA #$04 ; If so Invert Bit 2

CB54: LCB54 BRCLR 3,X,#$20,LCB5A ; BR IF NOT b5, MW4 (N.O. FAN)
; ... else
CB58: EORA #$40 ; If so Invert Bit 6
CB5A: LCB5A BRSET 3,X,#$40,LCB60 ; BR IF b6, MD4
; ... else
CB5E: ANDA #$F7 ; CLR b3, PWR STEER
CB60: LCB60 STAA L0038
;-----------------------------------------------
Posted on: 2012/12/13 3:03
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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First test failed. Bit 5 clears as expected with changes, but OD indicator still on. Must be another bit...

Current thinking is that $0036 bit 1 is controlling the OD indicator, and bit 7 is controlling shift light. Still need to verify.

C6D9: FDB $0036 ; 54, MODE WORD 2
; b0 1 = CARS ACTIVE
; b1 1 = MALF 14 OR 15 THIS START UP
; b2 1 = REFERENCE PULSE OCCURRED
; b3 1 = IN ALDL MODE 8192 LOCKED IN AND MODE 4
; b4 1 = DIAGNOSTIC SWITCH IN DIAG POSITION
; b5 1 = DIAGNOSTIC SWITCH IN ALDL POSITION
; b6 1 = HIGH BATTERY VOLTAGE-DISABLE MCU SOL DISABLE
; b7 1 = SHIFT LIGHT ON
;
;-----------------------------
Posted on: 2012/12/13 19:26
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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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Hey TB, I was hoping you would chime in.
I probably won't get a 87/88 in my hands until the season starts.
I've got feedback from a 87 owner, he choose to ignore the light without telling me. I guess all 87/88 are affected after all, when switching to ARAP.
Thanks a lot for helping out here!
Axel
Posted on: 2012/12/14 0:35
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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Tonight I confirmed that Bit 0 of $0036 is what controls the OD indicator when running $6E software in an 87-88 car.

; b0 1 = CARS ACTIVE

In $32B software this is $0035 bit 0:

; Bit 0 = 1= OVERDRIVE ON
; 0= OVERDRIVE OFF

I mistakenly called it bit 1 in my previous post but really meant bit 0. Sorry for any confusion.

My first attemt at clearing bit 0 resulted in a toggling of the OD indicator, so I knew I had the right bit this time around.

The fix requires preventing the bit from being set as part of the CARS (CAGS) logic in $6E.

Not really difficult to do, but it can be set in a couple of spots.

I was a bit suprised that the dash uses 8192 baud data, but the shift light was a clue, since this is only present in the 8192 baud data stream.

You learn something new everyday, I guess.
Posted on: 2012/12/14 1:57
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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Sequence of test changes:

First change was to replace the ADNA #$FB with ANDA #$FA to clear both bit 0 and bit 2.

CCB1: ANDA #$FB ; CLR b2, (DRP LAST 6.25 Ms)

This resulted in toggling of the OD indicator, so I knew I had the correct bit.

Next step was to eliminate the statement where bit 0 was likely being set:

E129: BSET L0036,#$01

This was done by inserting NOPs to replace the BSET L0036,#$01.

The OD indicator stayed off with these changes during my limited testing.
Posted on: 2012/12/14 3:19
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Matatk Re: 86-89 Digital Instrument Cluster "OD" light
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Wow that is impressive!!!
Posted on: 2012/12/14 3:34
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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After some thought, a cleaner and more efficient approach is to simply clear bit 0 instead of setting bit 0.

Just replace the line:

E129: 14 36 01 BSET L0036,#$01

with:

E129: 15 36 01 BCLR L0036,#$01

Somebody with an auto trans should evaluate to ensure correct TCC function and no interference from CAGS.
Posted on: 2012/12/14 20:25
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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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Hey TB, thank you for your input.
I know where to find bit $0036 and how to change it, but I lost you on this one: "E129: 15 36 01 BCLR L0036,#$01"
Where do I find that line in the prom, what address is that?
Thanks,
Axel
Posted on: 2012/12/18 19:19
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tequilaboy Re: 86-89 Digital Instrument Cluster "OD" light
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E129: is an address relative to the origin at C000.

This is the same as address 0x2129 expressed in raw hex form.

14 36 01 is simply the assembly code representation for BSET L0036,#$01 (expressed in hex bytes).

You should see the same 3 bytes starting at address: 0x2129 if viewing the bin with a hex editor.

15 36 01 is the suggested fix (again expressed in hex bytes): BCLR L0036,#$01.

To summarize: Change the 14 to 15 and save the bin with your editor again to recalculate the checksum.



Posted on: 2012/12/18 20:12
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Woodstock Re: 86-89 Digital Instrument Cluster "OD" light
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Thanks again! Now I got it.
I'll report back when we tried it in his 88 with AT.
Posted on: 2012/12/18 22:17
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Kckckc Re: 86-89 Digital Instrument Cluster "OD" light
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I realize that this is an incredibly old thread. I have an 87 auto and had a $6 (ARAR) tune burned for it. The "OD" light is on and torque converter lockup is not happening. Can anyone help?
Posted on: 11/26 6:47
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Matatk Re: 86-89 Digital Instrument Cluster "OD" light
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KC,

I'll have Axel look at the thread. He knows much more about tuning than I do!
Posted on: 2018/11/30 5:17
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