This is in regards to the '89 IROC in the signature.

I made a post about this earlier, but now that I think about it, it would probably be more appropiate in the electronics board...

Anyway, the subject says all about the symptom; if I let the car idle while sitting still, the temperature will climb so high that it forces the second fan on, but the primary never comes on. I am familiar with how the dual-fans on these cars work, so I know that the primary should be on long before the secondary kicks in.

Also, I have already checked and verified the operation of the following:

* The wiring between the fan and the relay
* The wiring between the ECM and the relay
* The relay itself
* The relay socket
* The fan motor
* The coolant temperature sensor (new)

All of the above is working as it should. To proove that, I can invoke the diagnostic mode on my ECM (by shorting the appropiate terminals on the ALDL), and the primary fan does turn on in diagnostic mode as it should. So that tells you right away that all the wiring is good, as well as the relay and motor. The ECM is also a new (well, rebuilt) unit that I got a week ago.

The strange thing is that I was actually able to test 14V across the coil leads on the primary relay at one point (when the engine was hot enough that the primary should have been on), but when I plugged the relay back in, it didn't actually click or anything. Then, just to make completely sure that it wasn't just a dirty socket or something, I turned the car off, invoked the diagnostic mode, and then went back to test the voltage across the coil leads again. This time, I got 12.8V. Then, I plugged the relay back in, and the fan came right on.

I don't know how I can be reading 14V while the engine is running and have the relay *not* power on, and then read 12.8V when the engine is off (in diagnostic mode) and only then have the relay power. My only guess is that it wasn't getting enough current when I read 14V to actuate the coil on the relay, although I don't know why that would be.

Any ideas? I've tested everything that I know to test, and this thing has got me stumped!

Thanks!

 

Sancho,

Sorry, I didn't see your last reply in your original thread. I wasn't giving up, but have been busy with a little head work.

Check the reply in your original thread.