I'm haveing a hard time reading your meter when you took the ground readings. Like shoebox said what are they, or can you get us a better pic.
-b

 

Ok, I will check this out after work tonight. One more quick question...

1. If the engine is hot enough, and the temp sensor reports back correctly, and the PCM provides ground to operate the fans; now you park your car and shut it off and take the key out. Are the fans engineered to run after the car is turned off like some newer cars do? Please verify.

 

No, they go off when the key is OFF.

 

Ok... after pulling the Cooling Fan #2 relay to stop the fans and letting the car cool down for a few hours I grabbed the digital meter. Here are my readings.

At the C100 Clip toward the PCM (20K OHM Setting on Meter)

"J" Dk. Green Wire = .65
"H" Dk. Blue Wire = no reading
"C" Green Wire = -.02
"A" Pink Wire = 1.24

The letters are the marked positions on the C100 clip. If a letter is not mentioned it means it had no reading.

So, I guess having a .65 reading on the dk. green "low-speed" fan wire signals a problem, huh? What could be causing this.. does it mean my PCM is shot?

 

What tells the PCM to "stop providing ground" when the key is off/out? Is there another type of "sensor" or switch at the ignition. Does the PCM have power when the key is out and ignition off?

 

IMO, there should be no ground coming out of the PCM (like you see at "J"). When they key is turned OFF, power to the operating systems of the PCM shut down. It still gets power from another source to keep the volatile memory stored, but no command functions of the PCM remain on.

Have you tried taking the red connector off the PCM and seeing if the ground is still present at C100? This will tell you if the wire between C100 and the PCM may be grounded. Just for the heck of it, you might pull the PCM BATT fuse and see if the ground is still there. I think you might have a bad PCM.

 

I haven't tried that yet... I will check it out tonight. Thanks.

 

Ok I took the red connector off of the PCM and the ground goes away so there is no short before the PCM. I pulled the PCM batt fuse and the ground is still there. Here goes more weird stuff.

1. With the battery disconnected from the car, I still get a .60 reading on the "J" green wire into the PCM... so there is definitely something wrong. When the car is running, and I pull the cooling fan relay #2 and check for ground the reading goes from .60 to .20 at 20k OHM. So, the PCM is providing a partial ground with NO POWER AT ALL, but the ground (ohm reading) at "J" green wire changes from .60 to .20 when the ignition is on and car is running... so this is essentially telling me that something is definitely wrong with the PCM because it should not provide any type of ground when the car is cold and initally turned on.

2. Just for the hell of it I disconnected the ECT sensor from the PCM and there was no change at all.. It behaved 100% the same.

3. If I let me car run, and it heats up to 225 or 226 whatever the correct temperature is, the fans do kick on and run at high with no problem at all.. they turn off when the car is turned off as well... so again, this is a problem that only pertains to the low speed fan operation.

4. Let me ask another question... who cares about the low speed operation.. i mean other than prolonging the life of the fan but running at half speed, what is the purpose.. let the car get up to temp and the fans run at full throttle.. I mean, if my PCM is bad what would it cost me to replace it?? And just for low speed fan operation, is it worth it?

5. Let's say I just wanted to do this.. I turn the ignition to 'RUN' or 'ON' and the car is running.. does the ignition provide a ground on some other wire when the car is on.. what I am getting at is I can just connect the low speed fan relay to this wire which provides ground when the car is running.. this way the fans will always run at low speed when the car is turned on.. and then they will switch to high speed when the proper temp is reached.. would anyone suggest this work-around???

6. I know that the problem is on the dark green wire "J" towards the PCM.. does anyone that owns a 97 Z have a meter.. can someone else just verify their OHM reading with the car off and on at this position??? I mean, then at least I would have a 100% definite answer.

7. One last one.. ok, so my PCM is showing .60OHM with NO POWER.. so what happened.. does the PCM actually have moving parts inside.. i mean, when it wants to provide ground on a circuit.. does it have some sort of relays inside of it to do that.. are the testable and or replaceable??

thanks in advance for anyone that wants to tackle all of my questions..

 

.... come on.. doesn't some one here work at a GM dealership or something... how would a certified mechanic tackle this problem based on this criteria?someone has to have some ideas! I think that I have been pretty thorough... if someone has a few minutes please lend the time.. i really appreciate it.. thanks!