Help! Newbe post. Another 1992 throwing sys, security, service asr lights.

[clugnut]

Hello forum! My name is Jon and I am a new member here. I have owned my yellow 92 M6 for 11 years. It has been a great car for me, although recently it has been giving me fits. I am hoping the tech geniuses on here might be able to give me some direction.


I been having an interrmitent problem with my car throwing out codes after it has been warmed up. It has now become very predictable, so much so that I can almost make it happen. The car needs to be driven for at least 20-25 minutes, until the temperature climbs up into the 210-225 degree range. Sometimes, the lights will come on at this point, but not often. Many times to make the lights come on, it requires that the car is parked and turned off, let sit for about 5 minutes, then attempted to be started again. This is when the magic happens. The sys and security lights flash, and the service asr light is lit. At this point, I can almost be assured the car will not start if I turn it over. The motor spins, but it will not fire. I know that I do not have spark when this happens; we checked it at the mechanics. After a cool down period, usually only about 5 minutes, the car will fire and I'll be on my way. If the lights come on while I am driving, the car will remain running and run normally. It does not stall or act funny, it only does not refire if shut off and not allowed to cool.

Using the excellant resources on this site, I scanned the CCM for codes. I am getting codes 41, 54, and 72. 41 and 72 happen every time the codes happen, and 54 is a new one. According to what I'm reading, 41 is ECM Data Comm lost, 54 is FEDS, and 72 is serial data link error. Sounds like the machines ain't talkin'. Most times, these are history codes, but the last time I scanned it, the car was acting up, and code 41 was a C41. Luckily at this point, the car hasn't left me sit for more then 5 minutes, but if I can fix it, that would be great.

I have been working on this problem for about 2 years. The mechanics haven't fixed it, so I'm going to try to learn as much as I can and do it myself. Off the top of my head, here are the parts I have replaced.

New opti
New ignition module
New coil
Remanufactored ECM (A Corvette Central article says most code 41's are caused by this)

I have service manuals on the way. I am afraid at this point the ECM is looking like a possible culprit, which scares me. I know they are scarce, and I do not know what I will do if I need one. Anyway, I appreciate this forum already, and if anyone could point me in a direction or offer some advice, I'm all ears and ready to learn. Thanks in advance!

 

[Hib Halverson]

It is unlikely that any of the parts you've changed so far are causing the problem.

Since you've already put a reman ECM in the car, while it is possible that's the cause of the DTC 41, at this point, it's highly unlikely.

You said you have the FSM on the way. When you get that, start reading all the info in it relating to the codes you have currently set in the CCM and the ECM.

This thread has piqued my curiousity. I'm on a road trip right now and away from the shop where all my FSMs are kept, but when I get back, I'll check back here.

My gut feeling is you do not have a problem with components. Rather you have problem with wiring and connections. In the meantime, I'd start poking around under the hood and under the dash and hard trim. Anywhere you find a ground connection, check it's cleanliness and tightness. First place to check is the big bolt holding the ECM grounds. It's on the left side of the engine, above the oil filter. Look for a big bolt with a bunch of black wires going to it.

 

[clugnut]

Thanks Hib, I'll start checking grounds. I also forgot to mention that while scanning, I did get an error message on module 4 when the car would not start.

 

[vetteoz]

Which is failing? ECM or CCM? - Corvette Forum

 

[Hib Halverson]

Thanks Hib, I'll start checking grounds. I also forgot to mention that while scanning, I did get an error message on module 4 when the car would not start.

What did the error message say?

 

[clugnut]

What did the error message say?

When I tested module 4, the screen where the codes are displayed just said Err. It only happened when I was scanning when the car was not starting.

 

[clugnut]

FSM's are in the mail! Yeah! I have tracked down about 4 grounds so far. I wire brushed and dielectric greased 3 of them, while that nasty sucker above the filter means I need some deep sockets and weasel piss to get the exhaust off. It feels good to be moving in a direction, even if it doesn't solve my problem, it can't hurt in the long run. Do anyone know the location of all the grounds in these things? I should check and clean all of them.


Thanks vetteoz for the link. That chat seemed helpful. A couple of guys seemed to have similar problems to mine. I need to learn how to use a voltmeter!

 

[gmjunkie]

FSM's are in the mail! Yeah! I have tracked down about 4 grounds so far. I wire brushed and dielectric greased 3 of them, while that nasty sucker above the filter means I need some deep sockets and weasel piss to get the exhaust off. It feels good to be moving in a direction, even if it doesn't solve my problem, it can't hurt in the long run. Do anyone know the location of all the grounds in these things? I should check and clean all of them.


Thanks vetteoz for the link. That chat seemed helpful. A couple of guys seemed to have similar problems to mine. I need to learn how to use a voltmeter!

 

[tmkassin]

You might also want to clean all the positive feeds connected together just under your battery. There is a ground there too from the negative side of the battery. I had this same problem with my 92. I had a bad ECM. There is a place in California that rebuilt mine, but I am at home and their info is at work. Good luck.

 

[clugnut]

You might also want to clean all the positive feeds connected together just under your battery. There is a ground there too from the negative side of the battery. I had this same problem with my 92. I had a bad ECM. There is a place in California that rebuilt mine, but I am at home and their info is at work. Good luck.

While I have the battery out, I might as well hit those too. Thanks for the heads up!

This is exactly what I needed! Thanks!!!!!

 

[John Robinson]

If this can be reproduced then I would suggest you get it in a mode were it is misbehaving and then raise the hood and shake the wires and wiring harness on the passenger side of the engine to see if this has any effect. If you take the cover off the passenger side of the engine you will find a large wiring harness with wires from the tps, maf, water pump temp sensor, a sensor in the air intake all going into the large harness. Peel the cover off the big harness back until you see a place were some black wires seem to come together. Those are all the ground wires for the previously mentioned sensors and it is those wires that the ecm takes its voltage readings from and adjust the whole system accordingly. Remove the black electrical tape on that bundle of wires and you will find them corroded. Cut them apart and reconnect with them. You may have to use some short pieces of wire spliced onto to them to make them all come together again. If so be sure to solder the splice and use heat shrink to cover it up.

One thing several of us have learned is that the ecm only reads the value of what is going to ground to determine what the sensor is seeing.

It can not be over stressed that the codes do not mean that the sensor referenced is bad but rather the ecm is not getting a correct signal from that circuit which can be caused by bad grounds, corroded connectors, broken wires, or were mister and misses mouse made there home during the winter storage and dined on the wiring.

 

[clugnut]

Quick update. Today when I was playing with the car, I grabbed the ecm and wiggled the wires a bit. When I got to the last connector (the one nearest the engine) the idle changed, the service asr and check engine lights came on, and the cooling fans kicked on. The fans might have been because it was warming up, but the others seemed as a direct result of the wiring. When I scanned the car, I still had my 41, but also at least three other codes coming up. At this point, I'm thinking I have a bum ecm rebuild on my hands, or a bad connector at the ecm. Thoughts?


Codes 41, 64, 72, and 73. Odd, I've never had 64 and 73, but it explains the low idle. Also, the coolant and oil temp gauges are not reading. Both say low.

 

[John Robinson]

Clean the connector with a contact cleaner. They can get corroded and not make good contact with the ecm. Also check the ecm ground strap connections and clean them. Until you have all the grounds cleaned don't assume the ecm is bad. The grounds are the life blood of this car.

This is not a put down but reread post no 11. The connector you are describing is were the ground wires from the tps etc go.

 

[Hib Halverson]

(snip)The grounds are the life blood of this car. (snip)

John Robinson gets the Tuesday afternoon "Beacon of Reality Award".

 

[clugnut]

Thanks guys. I forgot to mention that I did go through all of the grounds and cleaned them. All the other problems that popped up were do to the eprom popping out of place. Now, everything is back to the way it was, just codes 41 and 72, and a no start when 41 is active. I now have the FSM's, and have started going through them. Code 41 seems to be mostly conductivity tests. If it passes all those, do you start to assume hardware at that point? The grounds all seemed really good, so much so that I didn't feel the need to run any redundant grounds.



Oh, John. I did not go through that wiring harness you mentioned, but it looked great. I will attack that next time. Your advice is much appreciated; please know that I did read your post and your opinion is very valuable to me!

 

[clugnut]

Here is the best piece of info I have found for my problem yet. From the FSM for code 72:

"CCM Code 41 will likely be set along with this code if the problem is a short to ground or B+ on the serial data circuit"


Thats the problem! What's the solution? The ground thing I get. I guess I should check the ground continuity of the CCM. But what is a short of the B+ on the serial data circuit?

 

[John Robinson]

I reread your original post were you list the things you have changed. The connector on top of the opti needs to have the wires checked to see if one is broken. With the age of the wiring when you tug on the plug and wires to remove them they can brake. In your FSM it may refer you to chart C-4 which should be in section 6E3-C4-7. It looks like you can check the ground from the ICM to the ECM by doing a continuity check of the white wire by probing the A12 socket on the ecm connector the B wire on the ICM connector. The connector pin locations diagram is probably in section 6E3-A-11. You may want to have someone help you so you can shake the wire harness and see if you lose continuity. If you do that is your problem the ecm is not getting the signal from the ICM. Do not do a continuity check were the currant can back flow into the ECM. It is probably wise to disconnect the battery while doing continuity checks but back flow even from a voltmeter battery can fry the ecm. The hot only syndrome could simply be that the ecm is overriding some circuits until it gets information from other sensors and then it will activate them.


I believe the B+ is the hot wire

 

[Hib Halverson]

"B+" is "GMese" for any wire or connection that is at battery voltage.

The serial data circuit is how scan test data gets from the PCM to the DLC.

Start by looking for a short circuit between the serial data line and either ground or the battery.

 

[John Robinson]

"B+" is "GMese" for any wire or connection that is at battery voltage.

The serial data circuit is how scan test data gets from the PCM to the DLC.

Start by looking for a short circuit between the serial data line and either ground or the battery.

Thanks Hib I could only remember that it was the wire or connector that had voltage. As you say sometimes GM uses terms that are confusing but at least they stay consistent. At least he has the FSM now. For us that have used it for a while it is not so scary but for someone who has it for the first time it can be very frustrating. Have you ever written any articles on how to begin the process of looking up a problem in the FSM. I think it might be a very helpful piece of information. Many times the FSM is referred to as the place to go for answers but if you do not know how to read it then it is useless. For example I just looked up what B+ is in the General information section and it is identified as the positive terminal. Upon reviewing that section I find it has a lot of information. I am just bringing this up and in no way do I want this to take away from the OP and finding an answer to his problem. So please if this is something of interest to a lot of people then we should start a new Thread for this subject.

 

[VetteLuv]

Any resolution?

clugnut, Have you resolved your problem? I ask because my 92 just yesterday started acting in a similar way with the blinking SYS, Check ASR lit, cooling fan running (cold engine) and starter cranking but engine not starting. A "gentle" smack on the top of the ECM temporarily cured it but the problem returns later - after cool down or at speed on the highway - with engine shut off! Have read this tread for clues and want to know your results - please. Hate to have to "spank my baby".