Aux fan troubleshooting
 

Our aux fan crapped out just a day before a road trip. Ideas for troubleshooting? The 50A fuse is OK. Being that it's a PWM fan, not an easy TS. I disconnected the main connector and tried to measure output while spinning the fan but got nothing on any range of my DMM (I would have expected an AC signal).

INPA. There is a fan test option in there. If it runs the fan, then you have a faulty sensor somewhere. If it doesn't run the fan, you have a dead fan.

just went through all this. I found 14.2v at the fan connector. Did not have my usual DMM to check for control voltage from DME. I used a tone generator to trace back to DME which wire supplied the control voltage and I then took apart the connector to ensure a good connection to the DME. I purchased a TYC fan from Amazon and connected that to the fan connector, turned on the A/C and fan came on. I do not have INPA so this was my alternative way to troubleshoot.

Another symptom that probably points to the fan is it wobbles a lot. I'll worry about it after our trip - borrowed a buddy's 2006 4.4i X5. Should pull the trailer a tad easier (downside is it has the N62 valve seal smoke show...).

PWM makes the fan complicated to test.

INPA as mentioned is the best way, but there are a few alternatives.

The fan comes on briefly at cold start as a self test, check if it cycles to full speed then stops, on your first start of the day.

Also, putting AC to Max should cause the fan to turn on.

Fan doesn't come on at start, or when the AC is on.

Probably a dead fan then.

I experienced similar and with no INPA, said #$%^ it and just put in a new fan. Good thing it worked lol!

Back from vacation. Time to tackle the piggy. I'm starting to hate this old thing.

I would run 12 volts directly to the fan and see if it runs.

Unplug the AC pressure sensor down low next to the AC compressor on the hard line next to the frame rail. You can reach it easy from above. The fan should go to warp speed over 5 seconds if it is good.