1997 Chevy Cavalier cooling fan works, then it doesn't?

MATTM421968

MEMBER
1997 CHEVROLET CAVALIER
4 CYL
FWD
AUTOMATIC
139,710 MILES

I had the following issues to start. Blown head gasket, an inoperative cooling fan, erratic idle, oil pressure light on, low coolant light on, ETS light on, and codes for TPS (P0121 & P0122), O2 sensor #2 (P0141), cylinder 2 misfire (P0302).

I checked the alternator-Good. Replaced the head gasket, cleaned the inside of the intake manifold and replaced the intake manifold gasket, exhaust manifold gasket.
I replaced the Coolant temp sensor, cooling fan relay, new thermostat (180 degreee), added new coolant (about 60 % mix) reconnected the battery and cranked it over.
It Runs, still rough. But the cooling fan now kicks on at 208 degrees. Fan went thru several cycles on and off. Appeared to be working fine. Then the oil light came on and I shut the car off. Idle speed was bouncing between 560-620 RPMs by the Accutron CP9180 Scan tool I have. I found that the idle speed should be between 600 and 700 rpm, so I turned the idle speed adjusting screw in just enough to get it to stay about 600. Oil light is now off. Now the Fan doesn't work AGAIN! Temp hit 219 and I shut it down. I removed the fan relay, jumpered the fan power to fan motor connections under the relay and started it back up. Fan works, runs fast. I left it run like that for about 4 minutes to cool it off, then shut off the engine and continued to run the fan for another 2-3 minutes.
I rechecked the codes and found a P0300 random cylinder misfire, also the ETS light is back on and the low coolant light is still on (I have a new sensor for this. Forgot to swap it out).
What could cause the fan to suddenly quit working when it worked just 5 minutes prior?
Also. Something in this car was shorted to the point of needing to replace the ignition switch in the column according to the previous owner. I am begining to wonder about the PCM, would this be a reasonable worry?
I appreciate your help.

Matt

1 Reply

MATTM421968

MEMBER
5 POSTS

I found the answer quite by accident. The oil light was the sending unit-no big deal. The random codes and the ETS off light were generated by the PCM alright. There seems to be a water issue with these computers due to their location. The bottom front of the right side fender. Great place to put it GM, no wonder they are in trouble!
Anyway. First, I disconnected the battery ground. Then, I removed the front bumper cover (it is easier to do this than to try and work around it-it is secured with 5 plastic fasteners in the center and 2 10mm bolts on each side), remember to unplug the turn signal light from the bumper cover.
I then unplugged the horn electrical connector.
You can bend the horn forward just a little and the computer will clear it coming out.
Then I carefully removed the electrical connectors (there are 2-they are each held on with a bolt) to the computer, then I removed the 2 mounting bolts and slipped the computer out-CAREFULLY!
I looked for signs of corrosion on the computer around where the gasket on it is. There was corrosion-white powdery coating (the case is Aluminum)-so I removed the 4 screws removed the cover and then removed the 6 screws on the board itself.
NOTE>>>If you do this make sure to mark which screws go where. They are different sizes.
NOTE>>>If you do this-you must ground yourself somehow-this computer is like $525-so if you screw the pooch. Don't blame me! This is merely what I did, you do this at YOUR OWN RISK!
I found no water inside, but there was a good bit of corrosion around the seal, which comes off with the board.
NOTE>>>DO NOT tear this seal! It keeps moisture from entering the computer.
I cleaned up the corrosion with a wire brush, cleaned up all of the dust inside the housing-used air to blow it out and then wiped it to make sure it was clean.
The I reassembled the computer and reinstalled it. While I had the computer out, I checked every wire connected to the underhood sensors with a DVOM for continuity using the Hanes wiring diagram as a guide to wire color and circuit-all wiring was good.
At this point I think I am screwed and need a PCM, so I just take some dielectric grease and spread it into the computer connectors before I reattached them to the PCM.
I start up the car just for kicks and TADA! She runs. Still a little rough, but not as bad now. The fan now works again as it should and if I turn on the A/C the fan comes on like it is supposed to. All of the lights are out now. ETS light works right now, comes on if you shift into 2 or 1, then goes out when you go into 3 or D.
So, in short-little late for that now-if you have weird things going on with the fan or other sensors. Try removing the computer connectors and putting some dielectric grease on them. Corrosion inside the connectors will keep them from making good contact and the grease should help remedy that.
Just remember to disconnect the battery before doing anything to the computer!
Just think. PCM is $525. OUCH!

Read the manual and do things right.

I make no warranties about this procedure, nor do I take any responsibility if you screw up your car!

This is simply what I found to work for me, it may work for you as well.