The customer of Volkswagen Polo recently visited us with a speedometer fault. It had been looked at by another garage but they told the customer to bring it to an auto electrician.
To start with we put the car on our diagnostic machine to extract as much useful information form the vehicle as we could. In this instance there were no fault codes present, this is where real diagnostics has to be performed. A lot of people get the idea that we just plug the car on the computer and it tells us what is wrong. It would be great if that was the case and would make our life a lot easier but unfortunately a computer is only as smart as its programmer. A computer can only act on the information its programmed with and is not advanced enough to accurately diagnose a fault by itself.
When faced with this kind of fault we have to put our experience and knowledge together to trace the fault manually. Naturally we will check the wiring to eradicate it as a fault, but sometimes the fault may lay within a module itself.
We scoped the output of the speed sensor up to the dash panel and the signal was good. This led us to find a fault with the instrument panel module itself.
You can see circled in the picture above, one of the components had burnt out and had to be replaced. With a simple repair we had the cluster up and running again, saving the customer a lot of money on a replacement part.