Help! 1995 computer problem

[Mike Steele]

My '95 Corvette (automatic transmission) has been in a Chevy shop for two weeks. The technician says "the computer's not talking to the engine." OK...but does this take two weeks to find the cause? What remedies exist? I have contacted a company in Florida that will "rebuild" the computer. I seem to be missing something here. I welcome suggestions for solutions and shared experiences. Thanks!

 

[Schrade]

Get the mechanic to SHOW you what's goin' on.

A paper clip will tell you if there's a "serial communication error", in a minute or 2.............

 

[Hib Halverson]

Your service tech is going to need to give you a better explanation than that before anyone here can give you any specific repair suggestions.

In general, if the "computer is not talking to the engine", I'd be looking first a a wiring and/or connections problem. Once I'd determined there is no problem there, then I'd move on to the ECM itself.

 

[kpic]

Borrowed:

The 94 and 95 Vette's have an OBDII Diagnostic connector but are not OBDII compliant.

To enter diagnostic mode.
Short pin 12 to pin 4 or 5.

Turn ignition on. Do not start the engine.

Connector located above driver side right knee and pin out looks like below.

01,02,03,04,05,06,07,08
09,10,11,12,13,14,15,16

After turning the ignition on the CCM will display
any Diagnostic Trouble Codes (DTC's) and the module for which they apply in an automatic sequence.

CCM=Module 1
PCM=Module 4
ABS/TCS EBTCM is Module 9
DERM (Airbag) is Module A

Each DTC is displayed for 3 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 CCM and the other modules, "Err" is displayed.

The particular module being interrogated is indicated on the trip monitor, and the DTC's are displayed in the speedometer.

C4 Corvette Diagnostic Code Recovery Techniques

Here is a list of what the codes mean: 1992-95 LT1 trouble codes

Other references:
http://www.corvetteactioncenter.com...t-1995-error-codes-displayed-c72-h53-h72.html

Some of the group here are superb C4 techs; I'm sure they will guide you through it.

 

[Mike Steele]

Latest Info on my prior Help request

Well...my Corvette has been in the shop for a month (see below). The final diagnosis was that the BCU was dead. We found another one and it is en route. Having said that, I was told that the new one would need to be flashed...but that doesn't always work. If it doesn't, "the car will be scrap." Hard to believe. Does this seem to be fairly common? I am almost despondent.

My '95 Corvette (automatic transmission) has been in a Chevy shop for two weeks. The technician says "the computer's not talking to the engine." OK...but does this take two weeks to find the cause? What remedies exist? I have contacted a company in Florida that will "rebuild" the computer. I seem to be missing something here. I welcome suggestions for solutions and shared experiences. Thanks!

 

[ecss]

Well...my Corvette has been in the shop for a month (see below). The final diagnosis was that the BCU was dead. We found another one and it is en route. Having said that, I was told that the new one would need to be flashed...but that doesn't always work. If it doesn't, "the car will be scrap." Hard to believe. Does this seem to be fairly common? I am almost despondent.

If you get a replacement PCM (Powertrain Control Module) not sure what a BCU is the EEProm needs be flashed with the proper engine calibration file. There should be no reason the computer can't be flashed unless during the programming something happens like you lose power or interrupt the process. If the programming does fail during programming the computer will be useless and NOT THE CAR. There was a guy who would unsolder the EEprom and solder in a socket. He would then program a new EEprom which would allow you to reprogram the computer again.

The GM tech should have been using a Tech 1 a hand held tester to communicate with the transmission.
Using the tester you can activate the different solenoids and the torque converter clutch etc... and can verify if they work.

You've never mentioned what was the problem with the transmission. There are quite a few codes that can set if there are problems.

 

[Mike Steele]

Thanks, ecss

I'm told that BCU is the new acronym for the old CCM.

If you get a replacement PCM (Powertrain Control Module) not sure what a BCU is the EEProm needs be flashed with the proper engine calibration file. There should be no reason the computer can't be flashed unless during the programming something happens like you lose power or interrupt the process. If the programming does fail during programming the computer will be useless and NOT THE CAR. There was a guy who would unsolder the EEprom and solder in a socket. He would then program a new EEprom which would allow you to reprogram the computer again.

The GM tech should have been using a Tech 1 a hand held tester to communicate with the transmission.
Using the tester you can activate the different solenoids and the torque converter clutch etc... and can verify if they work.

You've never mentioned what was the problem with the transmission. There are quite a few codes that can set if there are problems.

 

[ecss]

I'm told that BCU is the new acronym for the old CCM.

The Central Control Module or in some other model vehicles called the Body Control Module is used to control and monitor electrical functions of the car. The PCM is what controls the line pressure and shifting of the transmission. 4L60E E is for electronic control.

Just what is the problem with the transmission?

The CCM is the module that reads the key pellet resistance, enables the starter relay and then allows the PCM to pulse the injectors. The PCM runs the engine and transmission.

 

[WhalePirot]

Frankly, I think the shop is spouting BS and should not touch that car! The stealers I'd dealt with take a week before they are finished getting my pristine Corvette all filthy... outside, then cannot fix the car or even drive to see IF they did. Chevy or not, they may neither be experts nor the best repair choice. Many dealers are training grounds for new techs, too.

ECSS and some others here are leagues ahead of these clowns.

 

[Schrade]

OP; WP is correct - the shop is BS'ing you.

A paper clip will show you EXACTLY what the DTC code is, or it will show that ECM [PCM for '94 - '96] isn't com'ming to CCM, which I think is DTC 51.

GO DOWN THERE, and get them to SHOW you.

And if you describe the problem here, we'll probably be able to diagnose it, even if you can't DO the repair...

 

[kpic]

51 is "Engine control module (ECM) – PROM" for a 94 Corvette OBDI; a 95 is 0BII.

 

[Schrade]

51 is "Engine control module (ECM) – PROM" for a 94 Corvette OBDI; a 95 is 0BII.

You sure it's OBII?

I think it's OBDII
===========================================

And I think '94 has no ECM. It's called PCM, with electronic control of tranny integrated into Powertrain Control Module, in addition to Engine Control...

that ECM [PCM for '94 - '96]

But there's a VERY teeny tiny chance that I could be wrong (see sigline )


Where's OP here anyway???

 

[kpic]

A 95 is not OBII compliant but the codes are a letter followed by numbers.

1997 through 2002:
U1000 CAN data bus -communication malfunction
P1153 Heated oxygen sensor (H02S) 1, bank 2 -insufficient switching
P1187 Engine oil temperature (EOT) sensor -voltage low
U1064 Body control module (BCM), CAN data bus communication malfunction

1995
U1000 CAN data bus -communication malfunction
P1153 Heated oxygen sensor (H02S) 1, bank 2 -insufficient switching
P1187 Engine oil temperature (EOT) sensor -voltage low
U1064 Body control module (BCM), CAN data bus communication malfunction

I'm not sure what it means but:

[TABLE="width: 88%, align: center"]
[TR]
[TD]

94​

[/TD]
[TD]

5.7L​

[/TD]
[TD]VIN P
[/TD]
[TD]CHEVROLET Corvette (OBD-I)[/TD]
[/TR]
[/TABLE]

[TABLE="width: 88%, align: center"]
[TR]
[TD]

94-95​

[/TD]
[TD]

5.7L​

[/TD]
[TD]VIN P
[/TD]
[TD]CHEVROLET Corvette (OBD-II)[/TD]
[/TR]
[/TABLE]

Maybe someone who works on them can explain it??

 

[ecss]

[TABLE="width: 88%, align: center"]
[TR]
[TD][/TD]
[TD][/TD]
[/TR]
[/TABLE]
[TABLE="width: 88%, align: center"]
[TR]
[TD][/TD]
[TD][/TD]
[/TR]
[/TABLE]
someone who works on them can explain it??

It was mandatory that all 1996 vehicles sold in the US be OBDII compliant. It's basically a set of guidelines on how trouble codes are retrieved, reported and what they mean.

OBDII vehicles have a basic set of trouble codes that are common to all vehicles and manufacturers. Each auto manufacturer may also have specific trouble codes pertaining to their vehicles.

94-95 Corvettes used a 16 pin OBDII connector but were not 100% OBDII compliant. GM was in the testing phase to get OBDII compliant and is why 94 and 95's have some OBDII trouble codes. Starting in 96 you need a code reader to retrieve PCM codes no more paper clip method.

 

[kpic]

ecss
Thanks!

I found a site which lists all the codes for everything GM. I did a ctrl F for Corvette and noticed Corvette had OBD 1 and OBD 2 listed for the same year. At the time my interest was my car, but two listings for the same year caught my eye.