VOLVO
ECM-721A - Immobilizer. Faulty signal
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
2 modelsS40 (2004–2013), V50 (2004–2013)
Show models by year and engine (2)
What does this fault code mean?
The immobilizer gets a faulty signal because the BCM's hardware serial number differs from the one saved in the ECM. The fault applies to the S40 (04-) and V50, and the starter cranks but the engine will not run.
Possible causes
- The programmed hardware serial number in the engine control module does not match the hardware serial number in the brake control module (BCM)
What you can do
- 1Read and note the code, clear it and switch the ignition on again to see whether it returns
- 2If you have a diagnostic tool: read the codes in the engine control module and see whether any other code is stored
- 3Has the brake control module or the engine control module been replaced recently? If so, their hardware serial numbers may differ
- 4Work on the brake control module (BCM) and its programming should be done by a workshop, as it controls the braking system
- 5If the fault remains, have a workshop with diagnostic equipment compare the numbers and program the engine control module if needed
Symptoms you may notice1
- The starter cranks but the engine will not run
General guidance for car owners. Diagnosis on the car can point to a different cause.