Has anyone ever had to replace their CCM to fix problems assoc. with the LCD not working right? I've been trying to fix all the problems with my '93 and I think I may be looking towards the CCM now. The digital gauges work intermittently and now the engine doesn't seem to want to fire. When the gauges don't work, I get the "sys" flash and the service ASR light, then they just go to "LO" and the engine won't fire for a while. I've checked the codes-code 41 (serial prob with ECM?) for the CCM and "ERR" for the ECM. Tried a new ECM, worked for a day or two, and now the problem is worse than before. Been trying to get datamaster and new-to-me laptop working but no luck, won't connect to ECM. My next course of action is pulling the dash apart and checking all connections associated with the CCM, especially grounds. Any suggestions are greatly appreciated and will be tried in short order, believe me! (Oh, pictures are sure to follow! '93 six-speed, red/red with Greenwood package and a weird hood scoop that is starting to grow on me for some reason.)

Thanks in advance,

KC-Shadetree Performance

 

if you get a new CCM, you have 100 miles to get it to a GM dealer so they can reprogram the odometer correctly.

I would agree, you are working on a real hard problem, and short of grounds, I like the CCM as a cause. I would try and chase the wiring between them, tho.

 

When you swapped out the ECM, did you use your existing Prom?

 

What is a CCM and what does it have to do with the odometer?

 

everything. The CCM is the Central Control Module. It stores the odo readings.

The CCM was introduced in 1990, and is the central computer between the ECM and brakes.

 

This may sound stupid..... but, what happens if you unplug it?

I just installed a CD player in my car and the guy at the shop told me the CCM was under the radio and if I unpluged it, the car would not run...

I didn't unplug it, but it was like I was working around explosives while I was installing my CD player...

 

Not under the radio, but more towards the firewall. It is the mother of all projects to get to.

Basically, it is the box that interperts all functions of the car ecm, vats are it's two most important functions.

 

Correct. My '95 had the CCM replaced under warranty due to the LCD dash going funky. The Odo is stored in the CCM. When you have it replaced the dealer is suppose to program the old Odo reading, and you VIN #, into the new CCM. They forgot to do my Odo so it started from 0 again and is currently only showing 1/2 the true mileage. At least I have the GM service record of when it was replaced.

 

Yes, I used a piggyback adapter and the chip that I've been using. Put in 30lb injectors, so I had to change the injector constant. I know they may be a bit much, but I had them laying around so I swapped them out. My old ones are going to be on their way to be cleaned soon though. I tried however using the orig mempak and the gauges still acted the same.

KC

 

Any tips or suggestions on getting the CCM out as far as the dash removal process? I'll prob tackle it the first part of next week. Tried to start it earlier, no gauges just "LO" and the engine turned over just fine, but wouldn't fire at all.

KC

 

The CCM is sorta under the radio... you have to remove the knee bolster under the dash, right side. It's back in there.

It is a pain, but not as bad as say... the heater core?

You cannot unplug the CCM and expect the car to run... I think the VATS alone would fail. The ECM is expecting a VATS ok from the CCM, so without that, the ECM would assume a VATS fail, hence, no start.

 

There is a security handshake between the CCM and the ECM at startup.
If the link between them is down at startup, the car won't start.
But, if the link goes down after the car is started, the ECM can run the vehicle standalone until you turn it off -- then, it won't start.

A new/refurbished CCM needs to be programmed for:
1) odometer reading
2) Option content of the vehicle (like ABS/ASR and C68 climate control)
3) VIN of the vehicle -- this is how you can tell if someone swapped a CCM to turn back the odometer -- the VIN won't match the vehicle.

Tom Piper

 

Tom, don't forget the vats security code.

It's accesibile from the driver side of the dash, at least it is in the 90.

 

Before you go digging out the CCM, I think you may be missing an important piece of info: C41. "Code 41 will set if the ECM does not respond to CCM polls for more than 600 milliseconds (three consecutive cycles)". The implication is that the CCM is working, but the ECM is not responding. Probably caused not by a faulty CCM or ECM, but an open in the serial data link between the CCM and ECM, or a short to ground on this connection. First confirm that your CCM can display a C12 (that is, that it is working) -- you may have to enter Diagnostic Mode 1.7 and clear the 41 first, but you should be able to go back to 1.1 and display a C12. Does the "off" LED on the climate control (C68) flash? This is also an indication of a fault in serial data communication. You should get the diagnostic chart for C41 specifically for your '93 -- it will identify the specific curcuit and wire colors to check. The only "special" tool you'll need is a digital volt meter.

Good luck.

Jac

 

Any idea where I can find this? I will try again to go through the diagnostic mode and clear the codes and see if it comes up with c12. After I clear the codes, before turning the key off it should say C12 correct? I don't think it has ever done that. I thought maybe I wasn't clearing the codes right. I've read several places how to do it but I don't think it is working.

Yeah, I can see the CCM because the guy I bought the car from said the radio quit working one day and pulled it out. It just lights up, no sound, nothing. With it unhooked I got the usual codes but plugging it in fixed the codes. It would then show that them as stored in history.

Thanks for the suggestions. I did read that C41 was the serial data error code, so I tried to hook up to it with datamaster to see if I could get something from the ECM but it wouldn't link up. Don't know for sure if I had something set up wrong or what, it was my first time trying to scan with datamaster. I've used WinALDL and tunerpro quite a bit, I'm just new to datamaster.

I will check all the wiring and keep everyone posted. Thanks again for the help.

KC

 

Well, I just went out and tried to clear the code 41 with no luck. I jumpered A to M, entered diag mode, had C41 at 1.1, pushed trip/odo to get to 1.7, held eng/met until ---, went right back to 1.1 and still got C41. I tried to clear the H72 out of the abs/asr the same way but that didn't work either. I am doing this right aren't I?

KC

 

Sounds like you are ok.

What you need at this point is a copy of the Helm factory service manual - It's the red book. www.helminc.com. The book contains the C41 trouble shooting you are looking for.

 

It looks like the CCM is functioning, but not communicating with the other components (ECM/ABS). Before you replace the CCM check the serial communications wiring. Looking at my '95s service manual, you're looking for a TAN colored wire, pins E13 and F12 on the CCM, pin 9 on the DLC connector, D29/D30 on the ECM, and pin 29 on the ABC/TCS controller. Also, pin A11 on the DERM module. All these pins are connected together can collectively are the serial bus.

A quick test of the CCM's communications would be to plug a scan tool in. If the scan tool can communicate with the CCM then it should be Ok and I would look for bad wires.

 

If you think the serial communications link is a problem, remember the ECM, CCM, ABS/ASR computer, and the C68 climate control all access that link directly.
The CCM controls the communications on that link.
So, you can disconnect the ABS/ASR computer and the C68 climate control from the system and the car should still start and run if everything else is OK -- you will get trouble codes on the brakes and climate control though. This way you can confirm that the ABS/ASR and climate control are not the problem.

As and added note, for pre-'94 vehicles, when a problem like this comes up, it is, by far, usually the ECM is the problem -- although, the problem with the digital gauges does start making me wonder.

Tom Piper

 

Yeah, I'm still thinking it's a wiring problem, hopefully just a loose connection somwhere. It seems like everytime I buy a car , someone has been messing with the wiring and most always screws something up. Slowly but surely I'll find it, I'm persistant as hell! I'm sure there's still a possibility that it could be the ECM. After all it is a reman. unit. I put in the old one and it seems to make no difference at this point. Should I go haggle with Advance and try to get it replaced to see if it fixes the problem?

KC