Save money and get the right diagnostics

Posted on July 18th, 2017 by Rob Marshall


It never fails to astonish me how many GEM members report frustration at receiving large repair bills for new parts, only for the original problem to remain. We tend to find this issue is prevalent among garages that prefer to spend as little time as possible diagnosing the problems, yet are perfectly prepared to replace components, sometimes blindly, in the hope that it ‘cures’ the fault.

Do not always trust what the car tells you

Usually, the first time that a car owner is made aware of an issue is through a dashboard warning light, normally one that relates to the engine management. As this lamp is a catch-all for a myriad of potential faults, diagnostic equipment is required to tell the technician what the car thinks is wrong with itself.

Yet, the car is not always correct, even though some technicians trust in their equipment blindly. While the vehicle’s computer might ‘think’ that a sensor, for example, is faulty, a loose wire can cause the same symptoms. However, the garage may find it simpler, quicker (and, maybe, more profitable) to replace the sensor, without testing it, first. Even if the garage in question lacks equipment that permits it to test engine sensor outputs with an oscilloscope (and good garages should possess such equipment these days) a simple multimeter, such as that pictured, can be used to test individual sensors – all that is needed is knowledge and data, both of which should be available to the average repair shop.

 Back to school

Recently, I visited the highly impressive Exeter College Technology Centre, where the Head of the Aerospace and Automotive Faculty managed to intercept a large selection of discarded sensors from various independent garages, which he tested with his students. Fewer than 50% of the sample was found to be faulty, which lead to the conclusion that certain technicians are relying too much on computer read-outs, rather than investing several minutes to test the original part, leaving the customer to foot the bill of replacing a potentially costly sensor for no reason.

What you can do

Should your car require a repair, it is worth paying a little extra in labour time to ensure that a fault is diagnosed as accurately as possible. Some garages will do this as a matter of course, while others will simply use their lack of either knowledge, or unwillingness to invest in their businesses, by simply replacing parts until either the fault is cured, or the customer becomes so infuriated that the car is taken away to somebody else. Be careful out there!