VY S2 Overheat - low speed fan

[MAG00]

My VY S2 Calais overheated one night. I pulled over as soon as a warning came up. Turns out my low speed fan hadn't been running. Turning on the AC switches on the high speed fan.

I have:

• Checked all fuses
• Checked wiring from engine bay fuse panel to fan
• Checked circuit from fuse panel to PCM
• Checked all relays, replaced the 5 pin fan relay, swapped the 4pin with high beams
• Hooked up 12v to the low speed fan and seen it run
• Started with dash engineering mode and checked the coolant temp (is this sufficient to confirm operation of coolant temp sensor?)

I'm stumped. It seems the PCM never energises the relay for the low speed fan to come on. The coolant temp readout on the dash seems correct. Busted PCM? Or does another sensor come into play?

Cheers!

 

[lout]

measure voltages at the relay base

 

[MAG00]

measure voltages at the relay base

Not much higher than 0V on the PCM controlled pin, been a few weeks since I tested, but it never energises the relay. I've checked that circuit back to the PCM and it seemed OK.

 

[lout]

you need a bidirectional scan tool and see if you can drive fan 1

 

[lout]

edit, the pcm supplies neg to the relay coil
do you have the relay coil positive

 

[MAG00]

edit, the pcm supplies neg to the relay coil
do you have the relay coil positive

Battery voltage to pin 85, near 0V to pin 86 (0.3V if I recall correctly)

 

[lout]

put a test light across 85 and 86 in socket
test relay by applying power to 85 and 86 on relay

 

[Havabigjuan]

this was a common issue in VS's, where the BCM/PCM switched negative to low speed fan relay dies (it did in mine)

some people put in a separate, manual, switch to ground the wire.... I have also seen set ups where they have it so the fan comes on with the brakes

Though, shouldn't your high speed fan have kicked in with the temp?