View Full Version : No Low speed fan root cause analysis

06-14-2017, 04:37 PM
Seems I have no low speed fan with or without the A/C on. I think the puller fan is working when the A/C is on. High speed come on about 3/4 before HOT. Possible that the relay in the IRCM is shot. What's the best way to tell? How do I diagnose this?

06-14-2017, 05:00 PM
A quick way to test the IRCM is to attach a code reader and run a KOEO test...the fan should hit both speeds in very rapid succession, then turn off.

As well, be sure to disconnect the harness at the fan, and jumper 12v hot to both speeds as a sanity check on the motor itself. I had a fan issue and thought it was the IRCM but it turned out to be the connector at the fan.

This is a way to test the IRCM circuits on car (example '90 SC):
Breaking the circut on wire #14 turns on low speed fan. Gounding wire #17 turns on power to the high speed fan motor windings. The fan should always be started in low speed (high pulls too many amps) and when the high speed is turned on the low speed should be turned off at the same time.

IRCM/CCRM Pin Outs (Main Fan Relays)
Pins 1/2 (black/yellow and black/orange) - Power to HIGH speed fan windings
Pins 6/7 (2 blue wires) - Power to LOW speed fan windings
Pin 13 (red) - 12V Ignition Hot (splice with 3A fuse if using external relays for fan)
Pin 14 (tan/orange) - Signal from EEC to IRCM for low speed fan
Pin 17 (green) - Signal from EEC to IRCM for high speed fan

06-14-2017, 06:06 PM
KOEO got no low speed fan just clicked and then high speed came on. Code indicated a 118. This say the engine coolant temperature sensor single voltage is too high. What even weirder is subsequent KOEO test hangs at the first click. I have to start the motor and the off again to get it to run.

06-14-2017, 06:11 PM
Can you repeat that test and see if both circuits at the fan connector light up?

Does the fan connector still have both lock tabs? Does it show any trauma? If you can jumper hot to both low and high and get the fan to react, I'd suspect the IRCM.

With everything connected what happens if you pull the ECT connector and run the engine? The fan should come on in that example.

06-14-2017, 06:33 PM
I'm not 100% sure which pins in the fan connector are for low, high, and ground. Anybody?

06-14-2017, 07:03 PM
One is ground - ID it by wire color black at the connector then jumper each of the remaining two, one at a time. Br/Yel is low ~ BR/O is high.


06-14-2017, 09:41 PM
Thanks for the help. I found it simpler for me to test the fan removed from the car. With my 60 year old eyesight and fingers it make it a lot easier. Also glade I did that because the fan was the issue. Lucky for me I had a spare. Issue resolved. Thanks for you time and help. Much appreciated. If you're ever in my neck of the woods, stop by for a cold one of your choice and I dip in the pool.

06-14-2017, 09:49 PM
Always good when an issue like this gets sorted.

Thanks for the update!