VW Touareg 2.5L 2006, intermittent cutting out and non start. No DTC’s recorded.
This vehicle was brought into my customer’s workshop and left, due to it’s intermittent problem. It had become very unreliable.
Due to the nature of the fault, the recovery agent and the general consensus in the workshop, was that the problem was most likely to be a crankshaft sensor failure.
The crankshaft sensor was replaced. It didn’t fix the fault.
When I first looked at the vehicle, after it had been sat for some time, it started and ran perfectly. We left it running for a while, with no faults occurring.
As I had other vehicles to look at, the garage chose to have the ECM looked at.
After the ECM had been checked and no faults were found, I was called back to look at the vehicle.
I started the engine and it cut out shortly after. I checked for DTC’s and there were none. I checked serial data and repeated the test. It did the same.
So now I needed to check some basic inputs at the ECM.
Out comes the scope.
My first look included crankshaft signal, main relay power supply and cylinder 1 injector voltage signal.
In the above image, you can see the start-up and run cycle followed by an event resulting in cut-out.
The next image is a close up of that event.
As you can see, the event shows voltage spikes on the crankshaft signal in time with the injector triggering. This ‘smacks’ of bad ECM ground.
The next image includes the ECM ground.
That image has shown our fault. The next image is a close up.
The next image shows the same inputs during a non start condition.
Of course with ‘hindsight’ I should have used my 4th channel to sample the ECM ground, on the first test, but it really didn’t make a difference to the diagnosis time, as the results were indicative of a bad ground.
Fortunately the ECM ground on this vehicle, is situated about six inches from the module. It is tucked up under the scuttle on the bulkhead and I was just able to see it. It was loose and I was able to secure it.
As you can see in the above, I have replaced the main relay supply with camshaft signal. You can see how the signals are nice and clean now.
Good result!
Mark Stammers Diagnostics 