Hello,
I have a 1993 coupe and am still bothered by an intermittent electrical problem.

I have spent hours and hours checking connections, ECM, Opti, CCM and others. I have the factory service manuals and under intermittents it mentions the possibliity of an open diode in a circuit. The schematics show diodes on numerous valves and on AC clutch. Has anyone ever known one of these to go bad on their car? I haven't even found a diode on the car yet, although there is supposed to be one on the AC cluth and others that are tucked into the harness. I think there is also one on the alternator. Another post mentioned changing a bad diode on his seat controls, and when I had my dash and console apart I checked the seat controls and found no diodes there (only capacitors)

My schematics show the snubber diodes on the canister purge and other valves as built into the valve. I have the Chevrolet FS Manuals.

I have cleaned all connections on the block, the frame, the power maxi fuse blocks and at the ECM and CCM. The car has never blown a fuse either.

I don't want to tear the harness all apart if I don't have to. I just want to know first that these diodes even exist.

Thanks

 

The AC clutch harness socket has a rubber boot and the diode is located inside the boot. If the diode fails shorted, you will blow a fuse for that circuit. If the diode fails open circuit you will hear pops in your radio when the device the diode is across turns off, and electronic devices (radio, cluster, ECM, various modules) are at risk from the inductive voltage spikes that occur when the normally diode protected device current is turned off.
You don't say anything about what is intermittent, so we won't be able to help you.

 

I may have found the problem. I was having a DTC15, all the wiring checked out and I even made a new special harness for the ECT. Used Datamaster on car and everything looked fine.

Yesterday I decided to pull the ECM grounds again and check them back to ECM. Wiggling wires and all. They are very hard to get to so I pulled the Cat Converter off to get to them. I had a trouble light on and I thought something looked funny with the Oil Temp Sender and when I pointed a very bright flashlight at the sensor I could see that it was cracked and separating. It was still plugged in good but where the plastic meets the brass it was broke and basically unplugging itself. This is a three wire sensor that has common wiring to ECT and TP. The black plastic part of the sensor will pull right off and the remaining part has a lot of hairline cracks in it. I have only owned the car for a couple years. This sensor may be the origional part.

The car would only act up after running for 20 minutes or more. There is also a lot of heat nearby and easy access for moisture to get to contact pins.

I'm heading to the Chevy store tomorrow for a new one and hopefully know something soon.

After pulling the ECM grounds off the block (TWICE) I would like to meet the engineer who decided where to put these ground connections.
I would like to place my hands gently around his neck and then squeeze real hard for a few seconds.

If this new sensor takes care of my problem I will let everyone know. This has been haunting me for a while. Thanks for the reply.