Cooling fan wiring


New Member
Jun 20, 2022
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just need some help figuring out the wiring for the 5.0L cooling. i know lo fan wire is the middle and hi fan is the outside wire. when i test voltages the low fan wire says 12v and the high fan wire says 8v when the fan is on low. when the fan is on high the lo fan wire says 15v and the hi fan wire says 12v. i figured the lo fan wire and hi fan wire would be energized separately so just not sure what’s happening. short in the fan? something wrong with ccrm or pcm? or is this normal?

edit: also have a chip the car so this next issue could be from that but when i leave the a/c off and let the car heat up low speed comes on super early around 160 and then high speed comes on 10 seconds later. could the entire issue be from the chip maybe?
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Well-Known Member
Feb 1, 2022
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Probably the chip strategy. People always thinking lower activation temps are better and they're usually wrong. But yes, the chip commands the ECU, which in turn commands the CCRM to energize the fan relays.

The CCRM is just a simple power device using high current relays for the fan specifically. It does other things like A/C clutch and fuel pump, but your voltage readings don't sound all that bad because you have to factor in voltage drop as the fan sucks down quite a lot of power (70 Amps total in the high state if I recall correctly). In my opinion though, 8v is essentially nothing especially when the car is running and the alternator is the thing driving current throughout the car at around 14 or so volts. The 8v reading could indicate something or nothing at all. I wouldn't worry about it.

The important thing is that either of the fan speeds actually work when they're supposed to based on perceived temperature (and pressure when you're talking about A/C) from the various switches. The low and high energize in tandem when either the A/C gets commanded on or the coolant temp gets high enough according to the tune configuration.

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