Great info there, thanks. I do have C68 Electronic Climate Control, but did not get a DTC for Climate Control, nor do I remember seeing the light flash. Could this lead you to think that the serial link is there and may be in a connection, as in my NOT needing a new ECM?
I looked around, it seems that Mid America wants my ECM to rebuild. As I have said before I like to do everything I can before I spend money. I have read too many posts where someone has replaced everything and the problem still exists.
Can you help with the connectors on the ECM, I have not seen that type of locking device and don't want to break them.

 

The C68 climate control LED flashing only happens once in a while.

My personal opinion is the best way to trouble shoot this problem is to eliminate the ASR and C68 climate control from the serial link -- disconnect them.
Because they are disconnected, the indicator lamps will come on -- ignore them.
See if there is still a problem with only the ECM and CCM connected -- look for the SYS and look for the "communications link error" on your Tech-1A. If these problems still exist after disconnecting the other computers, I am betting you have an ECM problem.
Also, if the ECM to CCM handshake doesn't take place and the FEDS shuts you down, that is a good indication that you have a problem in the ECM, CCM, or serial link.
Without the ASR and C68 connected, they can't be loading down the serial link.

Tom Piper

 

Thanks again for all the help. I am going to keep the Tech 1 in the car for a while. The last time I drove the car everything was OK. I'll wait and see if I get another DTC, I'll disconnect the ASR and reset DTC's and see what I get?
If the FEDS shuts me down, what do you think about power to the ALDL to run the fuel pump just to get home?
What can you tell me about the connectors on the ECM, how to take them off?

 

I'm not sure if the FEDS only shuts down the fuel pump -- it may disable the injectors too, but I'm not sure.

I don't remember how the connectors on the ECM work, but I also don't remember having any problem with them.

But, the fact that you have a FEDS problem is a very strong indication the problem is in the ECM, CCM, or serial link.
FEDS has nothing to do with the ASR or C68 -- except if they loaded down the serial link so the ECM and CCM can't communicate.


Tom Piper

 

Here is something else that may or may not be related.

Do you have an aftermarket stereo and if so, who installed it?

How this is related, my buddy put an aftermarket stereo in his C5. After a while he would get what he called a "flame out". The car would just die for no apparent reason.
Then sometimes his power seats wouldn't work, and sometime the car wouldn't start. The power windows would go up and down on their own.

A buddy of mine who is a GM Tech took a look and discovered that the installer of the stereo tapped into the serial data line, so there was 12 volts running through there fouling up everything.

The codes he had pulled showed no signals coming from the CCM and stuff like that.

 

Thanks again! Everybody!

No after market stereo, I had the Bose unit repaired by Dr. Don's over a year ago. The only thing I did recently was flush out the brake fluid with a Mity-Vac pump and change front brake pads. At first I thought maybe air got into the ABS unit. I ran all the test's on the ASR with the Tech 1 and everything worked OK.
The 2 codes I got where ECM and CCM not communicating. The FSM stated that if the Serial connection was dead at start up the FEDS would shut down the fuel. If the serial connection went dead while driving, FEDS would let me restart. My FEDS code came out as H, the car did start. So the serial connection did come back, intermittently if not for good.

 

Last night I tried to troubleshoot according to the FSM. I tried to get to the CCM, I gave up, What a PITA. The troubleshooting chart for the CCM codes was all wiring, I don't think I have a wiring problem. The car starts and runs, so the Serial link is there at start up. I plugged in the Tech 1 and read the same codes, then received an error message, No serial data from CCM, then received data again. The data comes and goes with the engine off and the car cold in the garage. GMPartsdirect wants $75.00 for an ECM "Plus Core" I still need to unplug the ASR/ABS and Climate Control to see if the data is steady?

 

It is my understanding that the CCM, being in control of the data on the serial bus, requests information from the ECM about three times before issuing the "serial link failure" when it doesn't receive it.

With my problem, even though the ECM was the problem, there was never any ECM trouble-codes or an indication from the ECM that it suspected a problem.


Tom Piper

 

I tried to troubleshoot last night. I disconnected the EBTCM and the car would not start. As soon as I connected it back up the car started and threw all the same codes. I did also notice the Climate control flashing. I still want to pull all the large fuses under the hood and do the rest of the dummy checks. You know the ones that make you say DUMMY after you've spent hundreds of dollars because of a corroded wire?

 

On my '92, I was able to pull the main connector on the ASR/ABS computer and the C68 climate control and my car ran fine until the engine warmed up and heat soaked my ECM.

I am very curious why yours won't run without it.

Tom Piper

 

When I had the problem with my ECM, it was difficult to pin the problem down to one module -- it takes two (ECM and CCM) for communications to take place.

I knew the problem was either the ECM or the CCM, but didn't want to spend money on the wrong part, so I emailed Corvette Fever Magazine. However, after not getting a reply for about a month, I decided to get a GM refurbished ECM and try it -- it fixed my problem.

About a week after fixing the problem, Chris Petris (owner of the Corvette Clinic in Sanford, FL and writes articles for Corvette Fever Magazine) called me about midnight on a weekend and discussed this problem with me.
He told me there wasn't enough space in the magazine to address my problem there, but he wanted to call me and tell me this was a common problem with the '92 and '93 ECM because he knew how difficult it was to determine the solution.

On another note, having been in electronics much of my previous life, an intermittent problem is the worst type of problem you can have.
Many times a defective unit is sent in as a "core" return.
And, the technician puts it on a test fixture for hours or days and the problem does not happen -- the next step is usually to call it good and resell it as refurbished -- problem and all.
I hate intermittent problems.
When I got my GM refurbished ECM and sent in my original ECM, I filled out a card describing the problem in detail and stating the problem was intermittent hoping the technician would be careful and put some effort into finding the problem.

Tom Piper

 

I am trying to source a ECM right now. I have prices from $75.00 to $300.00. If I can get the $75.00 unit I will buy it today, for $300.00 I'll keep looking around. I only drive the car once in a while, I don't mind letting it sit in the garage for a couple of weeks.
Thanks again for all your help.

 

I could not get a new ECM from Chevrolet, none available until maybe June? I found 1 on E-Bay for $150.00 and bought it. I installed it last night and everything is fine, no faults at all(KNOCK ON WOOD) I am going to drive it for a couple days and if everything stays the same I'll send my old unit to Mid America to get it fixed. The unit I bought from E-Bay is from a 92, so my confidence in it lasting is NOT HIGH.

 

Thanks for the update and good luck with that replacement ECM. Let me know how the Mid America rebuild experience goes if you don't mind.

 

I've been fighting this problem for over 18 months now. My car acts the same when warm or cold. I disconnected the ASR/ABS via the EBCM harness and I don't get the "loss of serial communications" error anymore. Per the FSM this would indicate the the EBCM is the cause since I get an H71 in the 9.1 with the wiring connected. Anyone ever have an EBCM fail?


Dave

 

I just wanted to make a contribution to this post as it helped me shake down the problem i had with my 92 LT1 Corvette. I had the ASR service light, Check Engine Service light along with the speedo and A/C shutdown. I reset by disabling the battery but it progressively went into failure sooner. It was if heat were a factor. I serviced the multipin connections with Caig Deoxit and did not help.
After reading this post and seeing the statements that the 92-93 ECM's were going to fail, I decided to take the chance and replace or have it restored. My vehicle has 68000 miles and am pretty sure that I had the original ECM.
I decided to send it out to http://www.enginecontrolunits.com . They offered a 24 hour turnaround (for most orders) at $219.95. I guess mine a "for most orders" as it took 10 days to get it back. They told me they send the Vette ECM's to a third party for restoration. (That was not stated on the website.) Anyway, I am past being upset for having to rent a car for a week and a half and am happy to report that the restoration job fixed my problem... I am sure my local Chevy dealer would have charged me at least a Grand for that repair...
Just to note that I would be wary of remanufactured units as they don't always repair the ECM's problems before sending them out to customers. Bad business...
So I guess I am ready for a beer to celebrate...
Mixalive
Austin, TX

 

I had the same problem and codes as Tom Piper. After hours of research and pulling my hair out I determined it was the ECM. I went through 4 reman ECMs before getting one that worked. On the fourth I tried a different company, Cardone, and that one worked like a charm. It was a very frustrating experience. Fortunately I only had to pay for one ECM and the others were sent back under warranty as defective.

My problem started over two years ago with the ASR light coming on intermittently. Then occasionally it wouldn't start on the first try. This summer it would have episodes where it would not start at all if the temp outside was greater than 25C. My old ECM would work if I cooled it off with some ice packs before starting.

I'm no mechanic or engineer but it doesn't make sense to me to put all those electronics and wires right next the engine under the hood where it gets so hot.

It would be great if someone on the forum with some electrical expertise could design a wiring harness extension so you could put the ECM in the car, under the passenger side dash for example, to prevent the recurrent heating and cooling it undergoes in the engine compartment.

 

Im in the same boat. Whenever I spin the rpms in the 6000 range my ASR and ABS light will come on. It seems to have no effect on the cars performance and doent come back on after a restart. Im just kinda of liven with it.

 

Mixalive

I have two ECMs for repair ( both with error code 41 Loss of Serial Data )

Fix this remanufacture your problem ?


my English is not so good, I do not have everything understood which you wrote

Is the Company enginecontrolunits OK ?


Raimund

 

I probably would not use them again. It looks like the website redirects to a different site now. I would rather have any work done by the company I send it to, not a second or third party.