OK ... replaced ECM and still the same problem
Thread Starter
Cruising
Joined: Sep 2006
Posts: 14
Likes: 0
From: Clovis, California
OK ... replaced ECM and still the same problem
The problem:
1990 - 39,000 miles
I pull a code that says my Computer Control Unit (the one under the dash) can not communicate with the ECM ... I replaced the ECM (Delco rebuilt)and I have the same code (yes I cleared the code and it came back) ... car runs fine but I get a flashing SYS light ...
Could the Computer Control Unit under the dash be bad (hope not looks like it isn't very easy to get at even with all of the dash parts I already removed)? ... could a ground or other wire be the cause ...
I took some of the dash apart and didn't see an wires that looked like they were lose or anything from the Computer Control Unit that looked loose ...
Thanks
in advance for any help ... as I said the car runs fine but the flashing SYS light just isn't right ...
1990 - 39,000 miles
I pull a code that says my Computer Control Unit (the one under the dash) can not communicate with the ECM ... I replaced the ECM (Delco rebuilt)and I have the same code (yes I cleared the code and it came back) ... car runs fine but I get a flashing SYS light ...
Could the Computer Control Unit under the dash be bad (hope not looks like it isn't very easy to get at even with all of the dash parts I already removed)? ... could a ground or other wire be the cause ...
I took some of the dash apart and didn't see an wires that looked like they were lose or anything from the Computer Control Unit that looked loose ...
Thanks
in advance for any help ... as I said the car runs fine but the flashing SYS light just isn't right ...
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
If the CCM and the ECM are not matching...it will cause this code no matter what you do. The SYS light will flash from here on out. Not sure what caused the code to start with unless you bought the car like that and in that case some one has changed one or the other, previously.
Are there any problems with the car that should not be...other that the SYS light flashing? Do you have a Factory Service Manual?
Are there any problems with the car that should not be...other that the SYS light flashing? Do you have a Factory Service Manual?
Drifting
Joined: May 2003
Posts: 1,979
Likes: 48
From: Lakeport CA
If you don't have one, get a FSM & it will tell you what steps to take for testing the connection...These are the type of things that make the factory manual so cost effective. Without one, you will probably never resolve this without throwing a ton of $ at repair shops & parts that you prob. don't need...
Instructor
Joined: Jul 2005
Posts: 140
Likes: 2
From: RI
Do you have an aftermarket stereo? This might be the problem:
http://www.corvetteforum.net/c4/dave8476/index4.shtml
http://www.corvetteforum.net/c4/dave8476/index4.shtml
Thread Starter
Cruising
Joined: Sep 2006
Posts: 14
Likes: 0
From: Clovis, California
I bought the car a couple of months ago and the SYS light was flashing at that time ... code 41 (CCM code not ECM code - can't communicate with the ECM). The code is a " lost communications via the ECM serial data circuit. The car had a remanufactured ECM installed at the time of purchase / I installed another newly remanufactured ECM and have the same code (code 41). I do have the factory manual ...
When I got the car the stock factory radio didn't work ... I took off the dash and pannels where the reciever is and found that a wire was loose and fixed that and the stock radio now works fine ... I also needed to replace the horn relay ... other than the SYS light flashing these were the only two things that needed fixing. Could probably use some new shocks (FX-3) since there seems to be some leaking from the rear shocks (I will do that durring this winter).
I have most of the dash removed so that I can get at the CCM and it looks like it has never been replaced ... from what I have read replacing the CCM isn't very easy and from what you are saying that might not help anyway
The car runs fine and is very fun to drive
(my first corvette .. I have six other cars and love to drive this car) ... I just happen to be very picky about my cars and this one last issue with the corvette is driving me crazy ...
When I got the car the stock factory radio didn't work ... I took off the dash and pannels where the reciever is and found that a wire was loose and fixed that and the stock radio now works fine ... I also needed to replace the horn relay ... other than the SYS light flashing these were the only two things that needed fixing. Could probably use some new shocks (FX-3) since there seems to be some leaking from the rear shocks (I will do that durring this winter).
I have most of the dash removed so that I can get at the CCM and it looks like it has never been replaced ... from what I have read replacing the CCM isn't very easy and from what you are saying that might not help anyway
The car runs fine and is very fun to drive
(my first corvette .. I have six other cars and love to drive this car) ... I just happen to be very picky about my cars and this one last issue with the corvette is driving me crazy ...
Thread Starter
Cruising
Joined: Sep 2006
Posts: 14
Likes: 0
From: Clovis, California
RRT vette ...
by the CCM and ECM not matching are you saying that since I have a factory installed CCM and now have a remanufatured ECM the two will never be able to comunicate and thus I will always have the CCM code 41 ... ?
I'm thinking there must be some problem with the serial data link since last night I tried to connect my OBD-I code reader up to the ALDL conector and it also couln't communicate with the ECM ... the factory manual also says that if there is a short circuit on the serial data link the 'C68 Electronic NVAC control head off button light will flash' ... I checked that last night and mine does flash (flash goes off after about 5 minutes).
Guess I will now need to check the serial data link connection wires and see if there is a problem there ...
by the CCM and ECM not matching are you saying that since I have a factory installed CCM and now have a remanufatured ECM the two will never be able to comunicate and thus I will always have the CCM code 41 ... ?
I'm thinking there must be some problem with the serial data link since last night I tried to connect my OBD-I code reader up to the ALDL conector and it also couln't communicate with the ECM ... the factory manual also says that if there is a short circuit on the serial data link the 'C68 Electronic NVAC control head off button light will flash' ... I checked that last night and mine does flash (flash goes off after about 5 minutes).
Guess I will now need to check the serial data link connection wires and see if there is a problem there ...
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I don't have a way to check the codes you state because I don't have a refrence to a 90-91 Corvette.
When I had my '91 the CCM stopped working. I had a shop in New Orleans check it out. The car would not crank and nothing on the dash would come on. This has been nearly 10 years ago, so it's not fresh on my mind. I watched as they removed everything to get to the CCM and started under the driverside footwell. The CCM is located near the inside firewall, as you can tell. They replaced it with a '90 CCM and the engine started right up after using a TECH 1. They told me since the ECM and CCM are not matching numbers, the SYS light would flash. So, from what I remember, you will need a matching CCM and ECM for the code not to be thrown. I have no idea if this is your problem or not. It could be something else like the CCM internaly. I would do what you can with the FSM to try and fix it yourself first.
Did the problem just start with connecting to the serial data link after installing the new ECM?
Sorry I can't give more information on this, but maybe someone else can help out. bogus (forum member) is usually pretty good with things like this and might be able to shed more light.
When I had my '91 the CCM stopped working. I had a shop in New Orleans check it out. The car would not crank and nothing on the dash would come on. This has been nearly 10 years ago, so it's not fresh on my mind. I watched as they removed everything to get to the CCM and started under the driverside footwell. The CCM is located near the inside firewall, as you can tell. They replaced it with a '90 CCM and the engine started right up after using a TECH 1. They told me since the ECM and CCM are not matching numbers, the SYS light would flash. So, from what I remember, you will need a matching CCM and ECM for the code not to be thrown. I have no idea if this is your problem or not. It could be something else like the CCM internaly. I would do what you can with the FSM to try and fix it yourself first.
Did the problem just start with connecting to the serial data link after installing the new ECM?
Sorry I can't give more information on this, but maybe someone else can help out. bogus (forum member) is usually pretty good with things like this and might be able to shed more light.
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Le Mans Master
Joined: Aug 2005
Posts: 5,002
Likes: 5
From: No Opti Here Tn
St. Jude Donor '06
Have you followed the diagnostic flow chart in the FSM???
That will locate the problem
Dont throw parts at it
A little leakage on the FX3 shocks is normal
If they are in fact bad you can have them rebuilt by Bilstein for about $100 each
Good luck
That will locate the problem
Dont throw parts at it
A little leakage on the FX3 shocks is normal
If they are in fact bad you can have them rebuilt by Bilstein for about $100 each
Good luck
Burning Brakes
Joined: Jul 2003
Posts: 873
Likes: 2
From: Whittier ca
I don't mean to hijack the thread, but will someone PULEEZE figure out this guys challenge! My 91 started the same thing yesterday (134,000 on the clock) and, hopefully, what will fix his will fix mine. BTW, I have gone through the search thing and c4guru's explaination on how to get the CCM codes is awesome.
I'll be watching this thread, since I need to go out of town Friday with the car and Wifey for 29th anniversary.
I'll be watching this thread, since I need to go out of town Friday with the car and Wifey for 29th anniversary.
Thread Starter
Cruising
Joined: Sep 2006
Posts: 14
Likes: 0
From: Clovis, California
I will be on travel for a couple of weeks but when I get back i intend to start going through the wire tests suggested in the factory manual ... I will post the results of what I come up with ...
The car has thrown this CCM code since I bought it ... no problems with the car running just annoying !!! As I said I have fixed all the other little things ... just this left to fix for now.
Thanks for the info on the rebuild of the shocks ... seems to be much less expensive than new ones.
The car has thrown this CCM code since I bought it ... no problems with the car running just annoying !!! As I said I have fixed all the other little things ... just this left to fix for now.
Thanks for the info on the rebuild of the shocks ... seems to be much less expensive than new ones.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
There's not much info on CCM's (command control module) on the internet. I would read everything that has to do with the CCM in the service manual. Might even want to purchase some literature on it. I do know that if you replace it, the odometer stored miles will be replaced with whatever mileage is in the spare CCM you get. Ex. if your CCM/car has 50,000 miles on it and you replace it with a CCM from a car with 90,000 miles on it. Your mileage will show up 90,000 miles. This is one of the things that can be canged to acutally change mileage on the car. Also if you replace the CCM you will have to change the resistance code on the key to whatever is stored in the CCM. Ex. if your key code is 7, and the spare CCM is 14....then you will need a new key that reflects the 14 resistance value.
If the car is not giving you problems then I would leave it be. Do some research on this and follow the FSM as much as possible to try and fix the SYS. I was hoping someone else could share there knowledge on this to clear things up.
If the car is not giving you problems then I would leave it be. Do some research on this and follow the FSM as much as possible to try and fix the SYS. I was hoping someone else could share there knowledge on this to clear things up.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
I am betting money that the CCM has lost a UART. UARTs (Universal Asynchronous Receiver/Transmitter) are communications chips. When they fail, the error you got is apt. Now, can you get any codes from the EBCM?
From what I am seeing here, the CCM is bad... Now, the CCM does need to mate to the ECM, but it's not THAT particular. If the CCM is from the right year, it should work. It may not work perfectly, but it would work. I don't remember the specifics here.
Now... this is where it get testy... if the CCM fails, and you buy a new one, ONLY the dealer can program the mileage back into the CCM. If this isn't done within 100 miles, it can't be changed... PERIOD. There might be a hack somewhere, but I haven't heard of it.
This might be of help. Try to read the various codes from the CCM... it might help...
C4 Guru - CCM Code Reading 1992/93
From what I am seeing here, the CCM is bad... Now, the CCM does need to mate to the ECM, but it's not THAT particular. If the CCM is from the right year, it should work. It may not work perfectly, but it would work. I don't remember the specifics here.
Now... this is where it get testy... if the CCM fails, and you buy a new one, ONLY the dealer can program the mileage back into the CCM. If this isn't done within 100 miles, it can't be changed... PERIOD. There might be a hack somewhere, but I haven't heard of it.
This might be of help. Try to read the various codes from the CCM... it might help...
C4 Guru - CCM Code Reading 1992/93
Thread Starter
Cruising
Joined: Sep 2006
Posts: 14
Likes: 0
From: Clovis, California
Thanks everyone ... I am going to follow the FSM step by step whne I get back from travel and will post what I end up with ...
If it is the CCM I think I might just let that SYS light keep flashing since the car runs fine for now ... the problem is with no serial data link you can not ever get to the ECM to read codes (so you never will know if the ECM throws a code) ... I'm hoping that I find out it's just a bad conection or ground associated with the serial data link wires ...
I tell you what my Model A might have been slow but it sure was easy to fix
Bogus ... thanks for the CCM code link ... you are correct, not much info on the net about the CCM ... and the designers couldn't have picked a more difficult place to put the darn thing ...
If it is the CCM I think I might just let that SYS light keep flashing since the car runs fine for now ... the problem is with no serial data link you can not ever get to the ECM to read codes (so you never will know if the ECM throws a code) ... I'm hoping that I find out it's just a bad conection or ground associated with the serial data link wires ...
I tell you what my Model A might have been slow but it sure was easy to fix
Bogus ... thanks for the CCM code link ... you are correct, not much info on the net about the CCM ... and the designers couldn't have picked a more difficult place to put the darn thing ...