Power is nothing without control

A Golf with a list of DTCs eventually ends up at Frank's manor

Published:  10 January, 2014

This month's story is one of triumph over adversity and in no small part the patience and good working relationship between the customer and us.

We have seen a few VW Golfs in our time and reckon ourselves to be both familiar as well as confident in their repair. However, the Golf that found its way into our workshop this month had been seen by no less than nine other garages and had trekked all the way from Newcastle upon Tyne to our workshop across the Pennines.

The Golf in question was a 130 Pd 'iJ' chassis with engine code ASJ. The vehicle displayed an intermittent loss of power due to several DTCs, the result of which set the n75 boost control solenoid to default value and thereby prevented any boost. The vehicle had been owned by our client for several years. It had been tuned up but was still beautifully smooth and displayed a remarkable torque throughout the range. For most of the time, a real pleasure to drive given its 86k mileage covered.

We also found that the vehicle came in with a variety of spares, ranging from several relays, in most cases more than one of the same part no, n75 solenoid... as well as other bits and bobs, including a cuddly toy and a dog cage!

PIC 2:The n75 control signal was as expected

The DTCs listed below suggested multiple component or circuit faults. It is our experience and opinion that this is most likely a wiring or common environment issue. The codes specifically focused on circuit or event failure and a short to power or short to ground problems:

? 46ao radiator fan circuit 1 open or short to ground

? 46oc relay [j17 low pressure priming pump] open circuit or short to ground

? 4691 air con interface short to battery +

? 4625 boost valve open circuit short to ground

? 4c03 relay low heating output short to battery +

PIC 3: Tapping the loom back was a task in itself

PIC 4: The car arrived with the back seat full of spare parts

PIC 5: The battery was below the recommended amp rating

In this instance, this is where trust and a good customer relationship will pay off. The customer located a used PCM from a Bora for £75. Programming it with a stock file and coding it to the Golf offered the final opportunity to prove us right or otherwise. Reassembling the vehicle and taping the loom back to OE standard was quite a task in itself (see photo 3) following an extensive drive cycle, the fault was eradicated.

This left us with a dilemma... Success weighted against the knowledge that the PCM could be faulty at a much earlier stage in our investigation. All votes cost £1 plus usual network rates, a very unusual problem, misleading evidence and a lifetime of experience. Which came out on top?

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