VOLVO
ECM-C121 - Communication, brake control module (BCM). Signal missing
System
Engine Control Module (ECM)
Volvo models this fault code applies to
This fault code has different meanings depending on model, model year or engine. Select the meaning that applies to your car.
Applies to the following models:
4 modelsC30 (2007–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)
Show models by year and engine (6)
- Volvo C30 (2007–2013)2007–2010Engine D4204T only
- Volvo C70 (2006–2013)2008–2010Engine D4204T only
- Volvo S40 (2004–2013)2004–2006Engine D4204T, D4204T2 only
- Volvo S40 (2004–2013)2007–2010Engine D4204T only
- Volvo V50 (2004–2013)2004–2006Engine D4204T, D4204T2 only
- Volvo V50 (2004–2013)2007–2010Engine D4204T only
What does this fault code mean?
The engine control module supervises the CAN link to the brake control module (BCM) and stores the fault when that communication is not working. While the fault is present the ABS function does not work, because the brake control module has no link to the engine control module.
Possible causes
- Supply voltage to the brake control module (BCM) is missing
- Poor contact, contact resistance or oxidation in the connections
- Open circuit in the high speed CAN wiring to the brake control module
- Internal fault in another control module on the same part of the network
- The brake control module does not belong to this car, for example a used unit with other software or hardware fitted
What you can do
- 1Start by reading the CEM and brake-module fault codes, and fix the CAN codes first
- 2Check that the fuses for the brake control module are intact and that it has power
- 3Check the connectors at the brake control module for loose contacts and corrosion
- 4Look for chafing and breaks on the CAN wires running to the brake control module
- 5Erase the fault code only once the faults in the CEM and the brake control module are fixed, then road test the car
- 6The brake control module controls ABS. If the brakes or ABS do not work as they should, do not drive the car; have a workshop check it
Symptoms you may notice2
- A text message and warning symbol appear in the display
- Warning lamps and warning signals behave abnormally, for example the Check engine lamp
What the fault can affect1
- No ABS function
General guidance for car owners. Diagnosis on the car can point to a different cause.