Got a technical question? Ask TRW’s expert

Q: I have just been employed as a mechanic in a successful MoT testing garage. This is my first job in a few years and I don’t want to appear out of touch! How do I test a vehicle with Electric Park Brake (EPB)? There seems to be no way of applying handbrake pressure without locking the wheels.

A: I can only speak for TRW’s system and not the ‘cable puller’ system fitted to cars such as the Citroen C5 and Range Rover etc. Technically, these systems are not really EPB, rather they are an electric motor pulling on conventional cables coupled to conventional calipers.

The TRW system uses separate actuator motors on each rear caliper, controlled via an Electronic Control Unit (ECU). And the TRW system has special software incorporated in the ECU for MoT type testing.

If you put the car on a rolling road and drive the rear wheels only the ECU detects that the front wheels are stationary but that the rear wheels are moving. It assumes that the vehicle is on a rolling road and puts the EPB system into test mode.

If fitted with one, this comes up as a message in the multi-function display on the vehicle dashboard. The tester can then either press or lift the handbrake-switch and hold in position.

The ECU will then apply the electric handbrake with sufficient force to obtain a reading on the roller brake tester, without locking the wheels.

Once the readings are obtained and recorded the switch is released. The tester then re-applies the handbrake in the normal way and the wheels will lock.

Test complete.

Please note: at all times adhere to the specific instructions and specifications as provided by the vehicle manufacturer.