Immobiliser active possibly ECU fault?

[bigddazzyd]

Hi all, 

2007 tdci, one morning engine malfunction and immobiliser active appear on cluster, car won't start or even crank, elm cable won't connect to  diagnostics, snap on code reader will read certain modules but not engine ECU, recovered to autoelectrians, his dealer level equipment will also not communicate with engine ECU, ECU taken out and sent away for testing, report that firmware was corrupt and would communicate with diagnostics on bench test. ECU put back in car at auto electricians, still won't communicate with diagnostics equipment, still won't turn over, still got immobiliser active message on dash, all wiring has been tested by autoelectrian and confirmed ok seems strange ECU behaves on bench test but not once back in car, any ideas or suggestions .......ford have quoted £1600+vat for new engine ECU but auto electrician isn't convinced this will solve the issue ......

[Tdci-Peter]

1 hour ago, bigddazzyd said:

ECU behaves on bench test but not once back in car,

Sounds more like a wiring loom or connector problem. If it does not connect from diagnostic socket to ECU, the first thing to test is the CAN bus resistance. It should be 60 ohms between pins 6 & 14 on the diagnostic connector when all powered down. This is due to the 120ohm terminating resistors at each end of the bus, so checks continuity of the bus wiring form one end to the other. One end is always the ECU, I think the other end is the BCM (or CJB) on the Mondeo/Smax, it is the Cluster on the Focus/Cmax.

If CAN bus is ok, then most likely one of the power supply or earth wires to the ECU is not making good connection. I assume all fuses have been fully checked.