Car clinic: Why does my BMW not always start properly?

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Q. My daughter’s 2009 BMW 116d Sport does not always start properly: sometimes the engine takes quite some time to start and once it would not do so at all. Her BMW dealer has replaced three parts so far, including the DME (digital motor electronics) relay, and she has spent in excess of £1,000, but the problem persists. BMW diagnostics do not seem able to pinpoint the problem. What should she do?
IK, Poulton-le-Fylde, Lancashire

A. Intermittent faults are the most infuriating type of problem to diagnose. Nevertheless, we do not think it is acceptable for your dealer to have charged more than £1,000 without curing the problem. The diagnostic computer may not be able to pick up this type of fault, but we would expect a good technician to start to investigate the basics with a multimeter (an electronic measuring instrument) and attempt to make a logical diagnosis based on knowledge and experience.

The DME relay is a fairly straightforward piece of equipment that switches the engine management system components on and off. It can easily be tested and if the technician was still unsure whether it was faulty, it should have been possible to substitute it with a used (but functional) unit to see if the car performed properly before permanent replacement.

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Your best option now is to find a good local mechanic or auto electrician who is able to investigate the car on the spot the next time it refuses to start. This is also the sort of roadside fault diagnosis that AA and RAC patrols are trained to carry out, so if your daughter is a member of either organisation, call it out next time.

You should write to your BMW dealer and BMW customer services asking why refunds were not given for parts such as the DME relay that were replaced when they were clearly not faulty. And when the fault is finally isolated, ask for a refund for all parts that were replaced unnecessarily. 


Sunday Times Driving car clinic expert: Tim Shallcross

Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motoring – read more from Tim here.

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