This may be caused by a bad light switch module -- the problem would be in the dash illumination dimming circuit. I had this problem several years ago and it seems to me I solved it by replacing that module. It is notoriously a troublesome part but is easy to replace.

 

That's what I thought as well, since it's a common problem like you said. The problem is he has an odometer error and everything "resets" when it blanks out.

You might have a BCM problem. What happens if you try to pull the trouble codes?

 

Thanks for the advice so far. Here are the codes. Bear in mind that the AC is not installed on this car at this time (it will be soon), and the 4.5L has been replaced with a 4.9L. Also the emissions stuff is not connected, but I might try to hook it all back up in the future. The problems with the dash precede the engine change, and the dash itself has been replaced with another one from a junker. That didn't solve the problem. I have also tried a ECM (I THINK that's what it was) from a junker but nothing changed. I switched it back.

Anyway, on with the codes:
47,121,334,335,336,337,441,448,556

The dash wasn't working the last time I drove the car but it magically was when I went out to get the codes now. I have wiggled every connection I can find or reach.

Thanks...

 

Correction: A central power supply from a junkyard car has been tried but not an ECM.

 

Anyone have an opinion on those codes?

 

So I tired to fix it today but no luck. There several ground wires connected to the electronic grounding spot under the hood. I think there's five of them, not including the one that goes to the battery. When the dash is working (which is intermittent) and I disconnect two particular ground wires, it stops working and acts exactly like it always does when it quits working. If I reconnect one or both, it works again (but only if it was working before). I looked at diagrams in the shop manual and those two ground wires are redundant. They come from the same exact place.

Anyway, this doesn't mean I found the problem. The problem most likely IS a ground problem, but not at the electronic ground connector under the hood. The problem must be upstream, some where on the grounding path that those two wires follow. Everything under the dash just looks like a pile of wires to me. I don't know how to sort it all out.

Am I EVER going to find the EXACT source of the problem amongst the myriad of wires???

 

Today the dash was working and I wiggled the connectors on the ECM and it quit working. I couldn't get it to start working again though. It could have been coincidental because the thing has a mind of its own and goes on and off whenever it feels like it. Maybe it's possessed.

 

Well, no one is responding anymore, but I'm going to keep posting because I think it may end up being valuable to someone else if I actually solve this thing. The steps I am taking may have value as well.

So last night I took a look at the circuit boards from the CPS that is in my car and the CPS that I had formerly tried that was from a junkyard car. They are not a match. So I can't rule out that the problem is in the CPS, because the other one I tried was the wrong one.

Everything looks OK to me with the CPS that was in my car, though. There is no obvious bad solder or smoked components and all the pins look fine. That doesn't guarantee it's good, though.

Tomorrow I will try to get the right CPS from another junkyard car. I know where one is at a U-pull place and the car recently arrived so the CPS might still be there and hopefully it is a good one. I think I can get it for around $20 since I will be pulling it myself. I might get the BCM and the ECM as well if they are cheap enough.

 

I had a similar problem when I bought my '88 Eldo. However not only the dash, but the ECC and all BCM functions went out along with it. It turned out to be the CPS. I pulled one from an '87 Seville in the wreckers, and it has been working fine ever since. I opened up the old CPS, and I could not see any evidence of failure. It looked fine inside, as does yours.

Your mileage being blank likely is the result of the cluster not matching the ECM. I think this was done to prevent people from installing clusters from lower mile cars.

So, what car did the CPS come from? It may not be compatible with your car, or it too may be defective.

Mike

 

Yes, it is exactly as you described. I may have given the impression that the dash goes out completely. That's not exactly true. It's still lit up, it just isn't receiving data. Kind of like if you disconnected your computer monitor from the computer. The lights on, but nobody is home.

The ECM and BCM data is not being received by the CCDIC either. This leads me to believe that 7 volts is not being delivered by the CPS. I had hoped to pick one up today, but I didn't make it to the yard. Hopefully I'll get a good CPS on Saturday.

There is one little glitch in my theory though. When I disconnected two ground wires under the hood, I got the same symptoms. Reconnecting one or the other brought the dash and CCDIC back online (but not permanently). That ONLY worked IF the systems were functioning prior to disconnecting the ground wires. This leads me to believe that there is still the possibility of a bad ground to the CPS. If that's the case, the CPS itself may be OK if there's a ground problem isn't internal within the CPS.

 

Today I swapped the CPS with one from a junkyard '88 Eldorado. The dash was not functioning prior to the change, but immediately started working with the new CPS. So I unplugged it and plugged the old one back in. The dash continued to work. So I plugged the new one back in. The dash continued to work, so I took the car for a drive.

The dash and CCDIC crapped out in about 5 minutes.

Maybe the problem is a loose connection to one of the pins on the connector to the CPS.

Well, there's one bright spot: I put in new plug wires, cap and rotor and now the car has major power. I mean, it had power before, but now it has much, much more.

I could probably sell the car for a good profit now. If it wasn't for the IPC/CCDIC problem...

 

Well here's the latest:

The service manual says to do test C3 if the DIC displays "system problem" and the climate control display is blank. Well, that is true, so I followed test C3. It said to jumper a wire across two pins on the ALDL ( I can't remember which ones), put the car in drive and then turn the key to start for 1 second. Then look and see what the odometer displays.

According to test C3, if the odometer displays zeros, then the CCDIC is bad and must be replaced. It DOES display zeros after following the test.

So should I believe it and replace the CCDIC? I think I can get one cheap from a yard about 60 miles from here, but I can't guarantee it's good.

Any opinions would be very welcome.

 

All connectors to all components have been removed, cleaned, inspected for bent pins and reattached. I've checked all fuses and all the ground connections I can find. Everything looks fine, but the problem still exists. I haven't replaced the CC/DIC yet, so that's next.

 

Have you checked your battery cables? They have a tendency to corrode internally at the battery connection and that could cause the symptoms you describe as the HVAC resetting to 75 degrees is what the car defaults to after a power interruption. Have a Reatta that did the same thing, went crazy tracking it down but was the easiest of fixes, just cut cable back to clean copper and re-connectorized it.

 

Yes, I checked the battery cables and all the connectors at the grounding block under the hood. Everything is clean.

Here's what I noticed today: If the dash and CCDIC stop displaying data (DIC will say "system problem", speedo reads zero, fuel flashes last known level, odometer and trip odometer read zero) and I turn the ignition key on and off several times, eventually everything comes back up.

Man, it just seems like a loose ground wire somewhere. But WHERE? Where haven't I looked?

 

Update: I replaced the BCM with another from a junkyard car and that solved MOST of the problems. I reused the proms from my old BCM because, well because that's what you're supposed to do.

Unfortunately I think the eeprom is no longer good and needs to be replaced. I've been having trouble finding a GM shop that does that sort of thing anymore. If I want it done right, I need a new eeprom and it has to be flashed to include my cars vin number and the odometer reading.

BTW, I determined that the BCM was faulty by giving up on all the diagnostic trees in the service manual and simply using my brain. I knew I had a breakdown in the data line and the only logical place that would give me all the errors I was having was the BCM. It is the central processor for the electronics system and if it starts acting up, multiple errors will occur.

 

Another update:
I know I haven't gotten many responses, but I will still update in case this is useful info for someone else with similar issues.

I have learned that there are two proms in the BCM. One contains all the info for the options on a particular car and it MUST be reused if you ever change the BCM unless you happen to get the BCM from another car that is an exact match. The other prom, which is the smaller of the two, is the eeprom and it just contains the current miles on the car (odometer) and the VIN for the car. If the eeprom becomes corrupt, you will get an b556 error code and the odometer will read "error". Good luck getting GM or anyone else to reflash the corrupt eeprom and good luck getting a new one. IT AIN'T WORTH IT.
If the odometer reading "error" bothers you, then switch the eeprom with a working one from a junkyard car. It will then read whatever the miles were on that car and it will also contain the wrong VIN. But who cares.
Now my car shows about 162,000 and the VIN is for an Olds Toronado.

In my quest to solve my dash problems I acquired a spare IPC and a spare ECM, both of which had nothing to do with my MAIN dash problem, but now I'm glad I have both. I have been having trouble getting this car to idle right and have replaced many parts in an attempt to solve the problem. I have a new ISC motor, fuel pressure regulator, fuel filter (twice, the second time after running Redline through the fuel system), distributor cap and rotor, spark plugs and plug wires. Also, throttle body gasket, EGR gasket, and a few vacuum lines. I believe ALL of these parts were actually needed, but the car still idled poorly. So today I decided to try the spare ECM. I installed it and did an idle relearn. The car DOES idle better. Not perfect, but better. I know I still am losing vacuum somewhere because the cruise control is weak and loses speed.

The only other code I am really getting now is a b336, which means the BCM has lost communication with the IPC. When this occurs, you can't read any IPC data in the diagnostics. Also, if I reset the trip odometer to zero, it will continue to read zero until the IPC regains communication with the BCM. It is an intermittent problem, which occurs every ten minutes or so. It also causes "service car soon - refer to owner's manual" to be displayed on the DIC. I believe the problem is with the IPC. Fortunately, I have a spare one I can try, when I get a chance.

That's about it.

 

Spare IPC took care of the final problem. No codes now except related to AC which is still off the car since the replacement engine was installed.

 

Awesome, glad to see it finally worked out. Persistence paid off.

 

Final update: The problems have remained SOLVED. All displays still function properly.

 

don' t know if you still follow your discussion. But I appreciated reading it. I am having the same problem .... just 15 years on