dual fans not working

tylerwerrin · 07-29-2010, 02:52 AM

i'm trying to rule out if my PCM is the issue in my fans not turning on for my 96 impala motor. i can get the fans to turn on if i:

A) run power straight to the fusebox from the battery with the relays popped out (to the power wires)

B) ground the pins from the PCM connector by hand.

there is continuity in the wires from the PCM relay control wires to the fuseblock -- the temp sensor appears to be giving me accurate readings.

Is it possible that the sensor is not grounding the PCM wires? if so, how can i figure this out? is it likely that the PCM's cooling circuit is toast?

any help in resolving this would be most appreciated!

algermilitia · 07-31-2010, 03:50 AM

If you pull the plug on one of your sensors, say the MAF sensor, your car will go into a default mode that always turns the fans on. I would say that if your fans come on in this mode, then they work and it's your PCM that's not turning them on. Also, try swapping out the relay with another. It could be the relay has gone bad. If you have a computer that is already tuned, perhaps someone turned them off, or set them to a higher temp.

OEM_TA · 08-02-2010, 01:12 PM

Factory settings for the fan turn on temps are quite high (226* / 235*).
Are you having an over-heating problem or just not seeing the fans turn on?

Turning on the AC should cause both fans to turn on regardless of engine temp.

tylerwerrin · 08-02-2010, 02:19 PM

i tried pulling the plug -- no dice. is there a computer program (diagnostic software) that can command the fans on/off? this would give me a definitive answer.

OEM_TA · 08-02-2010, 07:23 PM

The Tech-1 tool that GM dealers use will do that.
They are rare to find in the outside world.
The commercially available programmers I have or have seen do not do that.
Try looking here for more detailed information on fan operation.
http://shbox.com
It is geared towards 94 Camaro, but the Impala's system should be similar if not identical.

algermilitia · 08-02-2010, 08:13 PM

Have you swapped the relay with one that is know to work?

tylerwerrin · 08-03-2010, 01:26 AM

yeah, i tried swapping with 2 new relays, and a known working relay. no dice. when i grounded the actual relay control wires (pin a10/a11 on the c1 connector) i got the fans to kick on, so i know the relays are ok.

any other ideas of what it could be?

algermilitia · 08-03-2010, 02:48 AM

Ok, so there's power coming from the computer to switch the relays, but the computer isn't sending the signal out. I would say this may be happening because the computer isn't getting the proper signal to turn on. Like OEM TA says, stock temp for fans to kick in are about 235 degrees. Your guage is not the same device that the computer uses to measure tempurature. Maybe you have a faulty wire in between your coolant sensor on the pump and the PCM, or maybe the coolant sensor is faulty. Have you turned on your AC to see if the fans come on? If they do, your PCM is fine. The plug you pulled, was it the MAF plug? Anything that makes your SES light come on should force the computer to turn the fans on.

tylerwerrin · 08-04-2010, 05:16 PM

i swapped out the PCM -- fans work like a charm. Problem solved :-)

algermilitia · 08-04-2010, 09:55 PM

Cool! Possibly had a bad input pin connector on the PCM