Got a technical question? Ask TRW’s expert.

This month, Brian Newell looks at whether towing a car with EPHS can damage the pump.

Q: As an owner of a recovery service, I was called to recover a car fitted with Electric Powered Hydraulic Steering (EPHS). Due to the location, in order to recover the vehicle, I had to flat tow the car, with a pole, for a distance of two and a half miles. I have now been informed by the garage that because of the method of recovery and the fact that the engine was switched off, I have damaged the EPHS pump. How can this be?

A. It is not possible to damage an EPHS pump by towing the vehicle without the engine running. In fact I have never heard of anything like this before.

EPHS pumps only work when the alternator is running, i.e. when the engine is running. They do not work off the battery. Also, the amount of assistance they give depends on several factors, but mainly the vehicle speed and the angle through which the wheels are being turned. The higher the vehicle speed, the lower the assistance from the pump.  Towing a vehicle without the engine running just means the pump provides no assistance at all (as it would at speed), but no damage would be caused under these conditions. The car would just be very heavy to steer.