Strange intermittent electronic problem

As a retired avionics engineer I know that intermittent problems can be the hardest to diagnose. A few days ago when I start the car the climate control panel stays blank and the electric problem light is on. I have checked all fuses for a tight fit, shutting off engine for 30 or so seconds and restart no change. Within around 4 minutes the climate control panel comes on a/c starts working and electrical problem light turns off. Anybody else have this problem or have an idea of where to look?

Regards,

Richard

Is the display entirely blank, or does it show three dashes "- - -" where the temperature would be? If the latter, that indicates loss of communication with the data line. If it is blacked out, could be the ECC head failing, wiring between the ECC and central power supply, or a short or open in some other portion of the power wiring to the ECC.

If this just started suddenly, and is intermittent, I would suspect the ECC first. As it is a module with its own MPU and electronics on board, it is susceptible to the same problems that cause the IPC to fail (bad solder joints, marginal or failed components like capacitors that are prone to age related loss of spec value).

The ECC seems not nearly as prone to failure as the IPC in 90/91 models but is still capable of going south.

I'd verify voltages at the connector when the ECC isn't working to see if you are loosing your 12v feed to the module. If not, most likely the control head is going bad, assuming no display at all.

Tip: the ECC in 90/91 Reatta and 90-93 Riviera are the same part. The ones used in the 88-92 Toronado (non-VIC cars) look much the same but will NOT work in a Reatta or Rivi; and I have tried that out of curiosity.

KDirk

Thanks KDirk, when it fails the display is blank. For the past several months when I am driving I noticed that the display would blink off for less than a second, at first I would notice something in the corner of my vision and by the time I looked at it it was fine. It also started something else, it would ignore the controls and stay where I left it, usually auto temp set at 60. I would hit the outside temperature button and it would still show set point, then in a minute or two it would work fine. When it would blink off the system would keep running, unlike when it does not come on when starting the engine with electrical problem light and blank display which started about a week ago and has occurred about 3 times. Since the failure is so short I was thinking about leaving it in place until failure lasts longer, it would be easier to trace the problem. Do you agree?

Richard

That is an interesting failure mode.Normally, if the ECC drops communication (whether due to a bad connection, or an internal malfunction) the climate control mode will default to high fan, defrost mode (top vents on dash). That it is maintaining the last set temp and mode is atypical of what happens when the BCM and ACP (AC programmer module) loose contact with the ECC. Apparently, the ACP is maintaining last commanded operation even without the ECC present on the data line.

Despite that, I still suspct the ECC is going bad. It would be wise to check the connector at the rear of the control head first to be sure it is engaged tightly and there is no corrosion or oxidation of the pins, just for good measure.

I would note here that the ECC has two circuit boards internally: a CPU/interface board and the display/keypad board. These are connected by a ribbon cable within the ECC. It is possible, in theory, that the display/keypad portion is going out but the CPU part is still operating, this may explain the uncommon symptom you are seeing.

As far as leaving it be until it gets worse, yes, you could do that. I don't suspect it will do any harm, other than leaving you unable to control the temp and air delivery mode.

I'd also still verify you are getting consistent supply voltage to the ECC from the harness that plugs into it. This needs to be checked while the ECC is not working to be sure it isn't a power distribution problem. The ground on that connector should also be verified.If either of those don't check good, then that needs to be repaired first.

KDirk

I will do that. I got to thinking about leaving it in until total failure then I realized that is what made HAL 9000 kill everyone om the ship in 2001 A Space Odyssey. Of course I was 12 when it came out bit I think thats what happened.

Cheers,

Richard.