Radiator fan not coming on

I've been dealing with rising temps while under load lately and after a good compression test and two chemical tests I'm confident that it isn't the head gasket.

 

While chasing possible causes something I noticed is that with hot temps (about 3/4 up the gauge) only the passenger fan will run, the drivers side does not.

 

I've checked what I think are the right fuses and both fans come on in test mode. Anyone know why this might be?

http://people.csail.mit.edu/ilh/vacation/

 

See the 2009 FSM starting at page 1149. If I understand correctly:

 

- in test mode, ECU pin 18 is grounded, and the fans run in series (low speed). This uses fuses 3 and 22, and the sub fan relay. If I'm right (big if), this means those three components are working. Obviously you should check them anyway if my next conclusion doesn't pan out.

 

- in normal operation, ECU pin 29 is grounded, and the fans run in parallel (high speed). I don't know which side is main and which is sub, so I'd check fuses 4 and 26, and both main fan relays.

Turn your AC on. One might be for running warm and other might be for AC.

http://people.csail.mit.edu/ilh/vacation/

 

See the 2009 FSM starting at page 1149. If I understand correctly:

 

- in test mode, ECU pin 18 is grounded, and the fans run in series (low speed). This uses fuses 3 and 22, and the sub fan relay. If I'm right (big if), this means those three components are working. Obviously you should check them anyway if my next conclusion doesn't pan out.

 

- in normal operation, ECU pin 29 is grounded, and the fans run in parallel (high speed). I don't know which side is main and which is sub, so I'd check fuses 4 and 26, and both main fan relays.

 

Checked the fuses and both are fine. Don't really know the best way to check the relays.

 

Turn your AC on. One might be for running warm and other might be for AC.

 

When I tried this, both fans came on at a relatively low coolant temp of ~180F. When turning the AC on at a higher temp of 208F, the fan did not come on, which doesn't seem right.

 

 

This is probably a dumb question but both fans are supposed come on at high temps right? The FSM's temp profiles for fan operation just say "Radiator Fan Operation"

This is probably a dumb question but both fans are supposed come on at high temps right?

 

Yes. I tested thoroughly on my car, and either turning on the AC (at any coolant temp) or pushing the coolant temp above 200F will operate both fans.

 

To test a relay, apply 12V across the control circuit (terminals 85 & 86) and test continuity across the power circuit (terminals 30 & 87).

If you don't have convenient access to a 12V bench power supply, I would never advocate just throwing parts at a problem, but, um, relays are cheap.

Take a relay that is the same size from something that you know is working and swap them.

 

 

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I studied the diagram again, and I'm 95% sure your symptoms require that main fan relay #1 is bad.

I studied the diagram again, and I'm 95% sure your symptoms require that main fan relay #1 is bad.

 

Tested both main fan relays today and both are good. Not sure where this leaves me, ecu issue maybe?

Time for multimeter fun! I would start by checking continuity between main fan relay #1 and all of its connected components. If that bears no fruit, I would check voltage at each fuse and fan when the coolant is hot and only 1 fan is running. I would also test my hypothesis that ECU pins 18 and 29 should both be grounded at that time.