As the title suggests our Mk 6.5 (2007 1.25L) Fiesta has suddenly developed a fault where the OBD and Instrument cluster cannot communicate with the PCM module. It reports 'engine system fault' and 'high engine temperature' with the ignition switch in position II and obviously the engine won't start.

 

I cannot hear the PCM relay R11 click or the fuel pump prime. Would this suggest the PCM isn't fully powering up ?

 

I've buzzed out the CAN bus from the PCM connector to the OBD connector and both pins are connected from end to end ; the CAN bus measures 60ohms.

 

I've used ELMConfig and can connect to the GEM module on the MS CAN bus and the HEC (Instrument cluster) on the HS CAN bus BUT I cannot connect to the ABS module or the RCM module (ELMConfig doesn't fully support the Fiesta perhaps ?) so not sure what to infer from this. I'd obviously feel happier about the engine bay wiring if I could connect to the ABS module but as I've verified the CAN bus to the PCM I guess that's good enough.

 

I've checked fuses F16, F12, F21, relay R11 and checked the PCM connector for battery voltage on F21, F9, F8 (bridged M8 to battery negative) and GND on M42, M5, M8, F40, F7.

 

I've also swapped both instrument cluster and PCM with second units which I've been told are fully working (but haven't been able to verify myself) - the fault is the same.

 

Since I've verified the CAN wiring and even though I've verified relay R11 and the associated wiring it feel like the PCM isn't fully powering up ?

 

I'd like to get the car running again this weekend if at all possible but I'm running out of ideas. Does anyone have any thoughts or suggestions ?

 

Many thanks,

 

Jon

To close this thread it turned out that although I'd verified that the supply pins at the PCM connector were providing 12V there was a break in one of the cables in the loom and it was only hanging on by a couple of wires; enough to measure 12V with a high impedance input such as my DVM but the supply collapsed once under load from reconnecting the PCM. Repaired the faulty cable in the PCM loom in the engine bay and everything worked again !