Okay, Here we go
1993 Corvette with about 28k miles on refurbished ECM from 1993. Not many miles due to deployments etc.
Light come on, at first during hard acceleration. Now intermittently, after filling brake reservoir.
I looked at really old threads on this topic and listed items here that can be issues.
First off, no codes. Nothing
Master cylinder sensor? Replaced MC years ago, cracked.
Cleaned connector to master cylinder level indicator.
Brake Fluid Master cylinder- Full, really full and flushed with MityVac to put new fluid in. DOT 4.
Brake Pads- Still have 40-60%
Brake ABS sensors cleaned internally, and look good, no fraying or damage.
TPS- OEM. Did reset several times
Heat- I understand 92/93 Vettes had issues, and heat is an issue when right under plastic hood in sun. No real ventilation to cool of ECM-Not even sure what can be done.
Electronic AC code 02, door issue. Not sure what it is off hand. I think its the door that moves back and forth for cooling, heating.
I have the tach filter gone, and use Deltek system.
What else, Thoughts?

 

By ABS sensors I assume you mean wheel speed sensors?

Odd that there are no codes you can pull...

Are there any other symptoms or dash lights coming on or acting funny? Does it happen right away under acceleration or only when hot?

If it’s under acceleration it feels like a wheel speed sensor issue...but I’m just guessing! Hopefully someone else has better thoughts.

 

^ Yes, the wheel sensors for ABS. I always have ASR turned off during accelerating hard. 396 spins and or activates ASR if on , real easy.
I have tuned the ASR timing down so its not as aggressive.
Can a wheel sensor cause issues if ASR is turned off? With no codes?
But, It doesnt seem to be doing it when cold. More so when hot, but not all the time.
Then again, I drove in the heat of SC summer for 5 hours, and it never came on, this year.
Maybe it is a cold weather issue, and a ground/bond is loose?

 

Use some kind of ODB I tool to monitor wheel speed sensors as you move and make sure while going straight they are close in speed. You actually want to have someone watch while you drive. Do you really have an ECM from a '99? Does the ABS function properly?

 

Oops, typo. 1993 ECM.
What tool monitors wheel sensors?

 

Tech 2, or I think the Snap-On MT2500 does as I have both. I know the Tech 2 does.

 

Alright. Found a rather interesting video showing how to oull codes. I have been using TTS datamaster and jumping the terminals at the aldl for years.
Well, apparently there is another way. Jumper these two terminals, and you will see codes, that dont flash, and it tells you what module it is.
After doing this, you will get codes on the LCD of the dash.
Mod 1 is CCM, Module 4 is ECM and Module 9 is ABS
Here are mine

 

So module 9 in my FSM is ABS/ASR system section shows H72( Serial Data Link Malfunction) and H62 (Tach Pulses Malfunction). Module 1 CCM H 25 is Intake Air temperature issue. I took it out and its black as hell. So, I cleaned it real well, for now, with Electrical cleaner. Its now silver. K&N air cleaner since 1996 may have something to do with this being black.

 

And video.

 

ABS works great, as well as ASR. I took timing out of ASR system, so it wouldnt kill the power as much as it did when stock, using Cats tuner.

 

Ok, so, I have a 93 also, and I started getting “service asr” light coming on when engine hot followed by SYS on LCD And security light blinking (plus erratic speedo etc) all while engine running/driving. I had the same comm data link code. It eventually resulted in me not being able to start hot. Hit the ECM with my fist and fired right up fully confirming the culprit for me. This was due to failure of ECM to talk to CCM, ASR etc...

Now this is definitely jumping to conclusions and I’m clearly biased in this way so please continue diagnosing but you *could* be having the start of ECM issues.

You say you have a reman ECM? How long ago and source?

you at least have the FSM to diagnose the code properly...

 

My ECM was bought around 1999, from Eckler or MidAmerica but has less than 30K miles on it, and is mostly garaged. I think, due to me tuning it very often, that the culprit will be within the connection to the ecm. I will first check basic stuff, connections to ecm via harness..
FSM has a good flow chart. I will grab a meter from work, and check resistance and voltage as it suggests.
I hope its not a ECM.
SYS on LCD is usually a battery or charging issue.

 

FWIW I’m probably wrong. H72 I’ve been told can be a red herring And mean nothing (ie it is a byproduct of pulling codes). The Tach code might be more interesting. Apparently there is a tach signal to the ASR and perhaps that is your most likely culprit

Also, I definitely had the SYS message and other crazy things but again sounds like totally different problem

 

H72, Code 72 is intermittent. It just means something isnt meeting the 3 handshake talk.
Tach Filter is gone, so the DELTEK system I am using for ignition is replicating it, I guess. I have an extra brain for the Deltek system..I may swap it after/if codes return.
I cleared all the codes.

 

My reply has nothing to do with codes and is simply a thing I've run onto myself. My coupe is a 96, so may be different, as well. There is a big connector to the ASR unit very near the master cylinder. Check that connector. Wouldn't hurt to take apart and clean. Nothing ventured.

 

I think 95/96 are different. I am not home, but do you have a picture?.
these cars are heavily controlled by technology. Old tech.
need to drive them more. Otherwise they go to pieces

 

Sorry. I will not be able to photograph what I'm talking about for a few days. I figured by now somebody would have said this is different, my car vs your car. Likely Monday before I can do it.

 

No worries. I have been driving the car for the past few days after clearing codes and cleaning IAT sensor. The hottest the ECM got on top after driving in 77 degree weather, was 120 degrees F. I just stopped, turned engine off, then used heat meter.
Started at 69 degrees in garage, 105 wen I left to come home. . Drove 20 miles stop and go both ways.

Wonder if GM realized this when they made the 94 and up ecms. Arent they louvred aluminum..

 

Now to discuss my experience with ‘service ASR’ on my 93

it comes on occasionally on me, along with the service ABS light. Im not sure if something goes ‘out of sync’ during braking (whether ABS or non ABS operation, probably ABS). Once on , I believe the system is disabled.

When i turn the car off , and back on again, (without needing to do a batt disconnect/reconnect) the light will go out and system will function normally.

I also get both lights (service abs/service asr) 80-90% of the time when I do laptop
datalogging off the ALDL port (using an Aldl to USB cable and logging thru Datacat).

i have wondered if i need a tech 1 tool to reset something and then that will make these lights less likely to activate. I believe i read in the FSM service manual to use a tech 1 tool to reset throttle position? (Or something on the sort) on the ASR system when replacing components like a throttle body, throttle position sensor , etc

 

Mine does the same thing with service asr and abs light. Turn it off, restart and its gone.
To clear the codes I did the A to G on the ALDL.
I used another video but this does it too when jumping the A to G which showed me codes my TTS wouldnt or check engine light flashing ALDL troubleshooting we normally have used.
My AKM cable I use from yearsa ago, that I use for TTS datamaster does not have apin to go to G in the ALDL.