Fan Always Runs on High

[revhead347]

Got a problem on a friends 94' Cobra. The radiator fan always runs on the high speed. Doesn't matter whether the AC is on or off. As soon as the car starts up, the fan is running on high. We tried swapping out the coolant temp sensor. Anyone know a common problem that could cause this?

Kurt

 

[toyman]

Got a problem on a friends 94' Cobra. The radiator fan always runs on the high speed. Doesn't matter whether the AC is on or off. As soon as the car starts up, the fan is running on high. We tried swapping out the coolant temp sensor. Anyone know a common problem that could cause this?

Kurt

Stuck relay in the CCRM? Try giving the CCRM a smack to see if the relay will release. The ECT sensor is on the heater bypass housing (passenger side of engine). Fault codes will be 116,117 or 118.

 

[revhead347]

Cool. It probably is the CCRM, because the car isn't throwing any codes. Either that, or the computer has gone bad, which is highly unlikely.

Kurt

 

[HISSIN50]

Did someone do a manual fan switch or otherwise ground CCRM Pin 17?

 

[revhead347]

Did someone do a manual fan switch or otherwise ground CCRM Pin 17?

No, it just started happening. I guess I need to check to see if the signal wire from the computer to the CCRM is showing any voltage when the car is cold. And if not, then it has to be the CCRM.

Kurt

 

[HISSIN50]

As mentioned, you actually want to check that wire for continuity to ground, not 12V.

 

[revhead347]

As mentioned, you actually want to check that wire for continuity to ground, not 12V.

Clearly my knowledge base is not very good on how the system works. I assumed there would be a 12v power going to the relay to turn the fan on. Any other insights on the fan system would be greatly appreciated.

Kurt

 

[HISSIN50]

Yeah, you'd think so Kurt but it's EEC controlled and kinda funky. The low-speed relay gets a 12V signal (Pin 14 at the CCRM) but high speed uses a ground pulse. The EDF monitor is also a possible factor when things act up.

Just in case there's something helpful, here's some info:

94-95 Mustangs Electrical CCRM - Mustang-Tech

 

[revhead347]

Thanks for posting that. We should be able to trouble shoot it with that.

Kurt