Originally Posted by
pizzaguy
The FCM will run the fan at high speed ANYTIME the FCM is powered up (by turning on the key) if the ECU is not sending pulses to the FCM. This is an engine protection feature of the FCM - if the FCM is not being told how fast to run the fan, it runs the fat at full speed for the safety of the engine.
I am very new to Crossfire, but I can read the wiring diagrams. What ECU sends is a PWM signal, there is no logic in the FCM, no CPU as far as I know. If there is no ground PWM signal is being sent to FCM the fan should not run, unless there is a short to the ground in the wiring or ECU or FCM itself. And that is what factory service manual is saying - to check for ground on the PWM circuit. I did not find any info saying that fan runs 100% to save the engine.
Last night with ignition on (and battery charger hooked up and providing 10A) I tested ALL circuits for +12V I found no issues - ALL modules are getting power and proper voltage. Which leads me to believe it is the PCM internal issue. I will follow up.