Got any ideas on this problem

[KyRob]

My friend has an 06 Silverado that has 2 electric fans that cool the radiator. They will not shut off even after the engine is turned off and they will run til the battery is dead. He said he can stop them by unplugging either one of them after he turns the engine off. He switched the relays,fuses and has tried a bunch of other stuff to no avail. Posted it on FSC yesterday and had no responses at all so I figured I would post it here and see if any of you guys had any ideas.

 

Thanks,

Rob

[aflesch]

Check the relay. Remove the relay and look at the numbers on the bottom of it. You should have 30, 85, 86, 87, & 87a.

85 & 86 are the control wires. you need +12V on one and Ground on the other to turn the relay on (doesn't matter which way). IIRC the PCM grounds the relay to turn it on. Therefore you should have +12V on either 85 or 86 and NOT HAVE CONTINUITY to ground on the other when the fans are off.

 

First of all, if you pull the relay do the fans turn off?

 

If they don't:

you have a short to power between the relay pin 87 and the fans.

 

If they do:

If you DO have continuity to ground on pin 85 or 86 when the fans are running then you either have a short to ground between the relay pin 85 or 86 and the PCM or the PCM is commanding the fans on all the time for some reason.

 

Things to check if that is the case:

 

Do you have a check engine light on? (coolant temp sensor circuit problem could cause PCM to command fans all the time if it thinks the engine is too hot)

 

I have also seen a thermostat code command fans at all times (but that was only with key on)

 

If you don't have a check engine light on I would trace the ground wire from the relay pin 85 or 86 all the way back to the PCM. If you find the wire to be in good condition all the way back then you are probably looking at a bad PCM.

 

 

Good luck.

 

(Please remember that this is all based on the assumption that the PCM grounds the relay to turn the fan on.)

[KyRob]

I sent my friend the info aflesch. Thanks a lot for posting it.

 

Rob

[Duelin]

Has your friend installed any aftermarket accessories into this truck. If so I would be checking that also. These new truck aren't like the old ones. You can't just jump into any hot wire or ground. If you install something and get jumped into the Data Link Bus system you have no idea what it is going to control or not control.

[KyRob]

No aftermarket accessories. Problem just started a couple days ago. Oil pressure gauge is only thing on dash that is acting up.