for the sake of this post conversation, the specific computer module got shortened to just module. Essentially it's been focused about the engine control module (ECM) and central control module (CCM). I believe your referring to the Diagnostic Link Connector (DLC) located just to the lower right of the steering column.

 

You are correct, excuse my doofusness.

 

I need to re-read something but I believe there is a caution about NOT tapping on the ECM as a means of troubleshooting. The PCB inside is fairly close to the metal case and I believe it can cause an IC to short. (I'll look this up.)

On the C41 and H72, were these CCM codes and if so which module 1.1, 4.1 or 9.1?

I can make some assumptions: the H72 is from the 9.1 module which is a Serial Data Link error.

If the C41 is from the 1.1 module that is an ECM Serial Data Circuit (loss of communication). The serial data circuit is the communication link between the CCM, ECM, EBTCM and H68 HVAC if you have electronic air.

If the C41 is from the 4.1 module that is an Ignition Control Circuit short or open and comes from the ECM.

The ERR on the speedo indicates there is a communication problem between the ECM or ETBCM and the CCM.

The SYS is because the C41 is a current ocurring DTC.

If you wish to test the serial data links to the ECM, there are two as they run parallel (dual paths). But something to consider, a Tech 1 can run a test on the serial ports via the DLC. Most dealers charge about $100. to do this. Otherwise your looking at a good 4 hours to pull the CCM out and re-install it. The point is before you launch into this is, it may be cheaper in the long run to have them run the test on the serial lines and if they are good your not having to rip out that main computer.

Why do I say this because I went through it. Only it took me longer than 4 hours, conservative its four hours having done it longer not having done it. And, all to find out the continuity on the two parallel serial lines was good, as well as the ASR. In other words a lot of work just to verify it was ok. I think the next time I get this issue I would use the Tech 1 to verify the serial link and if found good troubleshoot the components again.

Now that fact your getting all these communication errors it sure sounds like the CCM is having a problem.

 

My ECM went bad while driving, the "SES" lighten up, and the car was going really bad, after reading a lot of forum posts about this problem i find out that if i tapped the ECM the car was running fine, tapped the ECM again and the car went bad. I swapped the ECM so this part is ok and the car runs fine all the time now.
The codes are: C41 and H41 in module 1, ERR in module 4, and H72 in module 9.

I had the car in for scanning, but the guy could not read any codes due to serial data problems he told me so that did not help me.
I will put the car in for the winter this week, so i have the time to troubleshoot but i am not sure about the wiring because my chilton manual does not have any wiring diagram for the ECM/CCM. I still think i might have a bad wire somewhere between the diffrent modules..
Thanks again 93JetJocky

 

Great thanks for the info that helps. I'll post that diagnostic info with the pinouts to test. If I have a few extra minutes before I leave for work here in a bit I'll try to put it up for you, otherwise a little later either lunch or this evening. I'm sure you probably have done this, but did you examine the pins of the ECM to ensure there are no bent pins? Hopefully you'll get it resolved before it is put up for winter. Did they replace the CCM or not? I know you mentioned the ECM has been swapped a few times.

 

Well, I have only replaced the ECM once and checked the pins , the CCM is not replaced in my case.

 

You'll want a DVM with at least about 30" leads for both the + & -. You can set the DVM on the door sill and pin the ECM and the CCM this way to check continuity.

First step is to verify your getting ERR when 4.1 is displayed in the diagnostics mode, which you did.

(If you don't have the connector pin-outs for the ECM say so, and I'll post a picture.)

- Turn the ignition OFF
- Disconnect the ECM connector "D"
- Disconnect the "GREEN" CCM connector
- Test terminal E13 from the CCM to D4 of the ECM
- Check continuity

(No) - Repair open in CKT 800 to CCM pin E13.
(Yes) - follow the next set

- Test terminal F12 of the CCM to D4 of the ECM.
- Check continuity

(No) Repair open in CKT 800 to CCM pin F12.
(Yes) - follow the next set

- Test terminal E13 of the CCM to ground
- Check continuity

(No) Repair short to ground in CKT 800
(Yes) - follow the next set

- Test terminal E13 of the CCM and Ground (you can also use a test light here but a DVM in volts mode will work as well)
- Turn the Ignition ON
- Test light on or battery voltage (about 12.6)

(yes there is a light or voltage) - repair short to battery + in CKT 800
(no there is no light or no voltage) - Repeat the above series of steps except use terminal D15 where D4 is called out on the ECM

If your showing good continuity then test the link to the ASR (EBTCM).

The EBTCM is located on the passenger side wall of the compartment that houses the ASR modulator.

Assuming you cannot communicate with the EBTCM:

- Ignition OFF
- Disconnect the EBTCM
- Ignition ON
- Use a DVM test the voltage between terminals 4 and 3.
- Is it about static battery voltage (B+)

(yes) - repair short to B+ in CKT 800
(no) - follow the next procedures

- Ignition OFF
- Check the resistance between 4 and 3
- Is it less than 5 ohms?

(no) - repair open in CKT 800
(yes) - follow next procedure

- Check for a poor or faulty connection at the EBTCM and the DLC.
- Check continuity between EBTCM term 4 and the DLC term M.

Notes: If intermittent try wiggling the wires will performing the above test.

A CCM DTC 41 will likely be set along with the ABS/ASR DTC 72 if the problem is a short to ground or B+ (battery voltage) on teh serial data circuit.

If ABS/ASR DTC 72 is set and the CCM DTC 41 is not, the malfunction is likely to be an open between the EBTCM and the CCM.

Lastly, CKT 800 is the link terminal 4 from the EBTCM (tan wire) through two connectors (C400 and C210) then goes on to terminal M of the DLC, the tan wire to the CCM. There is a junction there named S222, one wire to the DLC term M, tan wire 800 back to the EBTCM, tan wire 800 to the CCM and then the detailed following: Serial Data 1 and 2 of the CCM, Serial Data Link term 4 of the EBTCM, Serial Data link 4 & 15 of the ECM and lastly Serial Data link terms C9 and C10 of the Electronic Air (only).

If you need the schematics, I'll get you a picture of the two of them.
Something to consider, purchase the GM Service Manuals rather than using Chilton's.

Hope this helps.

Oh I forgot, don't back pin connectors. To test the ECM pins I used a tiny nail that fit perfect into the terminal or you can buy the J tools for these tests (I have the reference #s if needed). I just inserted a tiny nail into terminal D4 and D15 then clamped the test probe to the nai. Then worked from the inside by front probing the green connector.

 

93JetJocky !

what can i say, thank you a lot !! Now i know how start and where

 

I'm not having much luck getting decent pictures of the schematics. This one was the best I could do, it is the associated schematic that goes with the DTC 72.

On the pin out of the ECM connectors they go left to right upper to lower; 1-6, 7-11, 12-17, 18-22. They are color coded A is gray, B is red, C is green, and D is brown. You'll be looking for D4 and D15.

 

Thx

 

Just a note to anyone interested. If you want any pictures that have been posted, be sure to copy them to your local system, as I will be cleaning my FTP site this evening which will remove all posted pictures.

Thanks.

 

I assume that "continuity" means contact? And between E13 and ground it is not good contact.

The reading on the DVM was only 5.0V ? Should it not be like battery voltage?
But this is maybe the fault not any contact with ground for E13, and i have 5.0V were it should be 0V ?

 

Continuity-ohms. When you have continuity you should read 0 ohms.

Verify your testing against a known good ground. You should be able to reach the negative battery terminal to test this function. Or use a test light to see if it illuminates.

 

Ok, i did not have 0 ohms between E13 and ground, so thats a fault right?
Any comments about 5.0V and not actual B+ ? I think this will be a long winter
Btw, i will pick up my GM shop manual tomorrow.

Thx 93JetJocky

 

Well let's hope not too long of a winter.

The continuity test between E13 and ground with a No answer results in the next test which test for voltage on that circuit. Now the fact that you got voltage when you turned on the ignition it won't be battery voltage (and I may have been a little misleading earlier). But look at the schematic you can see that your on a data line from an output of the CCM, so it certainly isn't going to pass battery voltage, it's more like ±5 volts. The test is specific that it calls for a test light on that test phase, but a DVM is capable of measuring any voltage a test light would react to. Long winded but hey I'm known for that eh, concluding your seeing voltage there and you should not.

One other note about continuity and measuring ohms, it doesn't have to be exactly 0 to indicate continuity, sometimes you could actually see 30000 ohms but on that type of circuit it would still indicate good continuity. It just depends on the circuit. So if you saw 0 thru say .05 that still indicates good continuity.

According to the diagnostics as I re-stated them from the charts for you, if you got continuity at the test from E13 to ground, then you have a short to ground in the circuit 800 (refer to schematic above). The 5v your seeing from the ignition on test is not valid as it is the next step provided you got no continuity from the E13 to ground check.

I hope I'm making sense.

Anyway to sum it up, look for a short to ground on the tan wire from the ECM to the HVAC to the EBTCM to the ECM they are all on the same circuit that is what 800 is. I'd look for chaffed wires, faulty or marginal connections at the connector, bent pins, broken or exposed wires. And follow the road map of the schematic. Check continuity along those circuits. Example by testing between E13 of the CCM and D4 of the ECM will tell you if it is along that wire. If not move to the next one, i.e., F13 to D4, then look at E13 to 4 of the EBTCM.

I'm glad your getting the manuals. Your going to find they is worth their weight in gold when it comes to wrench your own vette. I'm not just spitting this all out from my head, I reading the manuals and using my experience of servicing one or another of these items to give you some guidance. It's studying the manuals that helps.

Also there's a old saying about troubleshooting electrical problems, don't apply a whole bunch of logic to it, most times it's something very simple and the solution is generally very simple.

Good luck.