Buying a car

This takes ten seconds and should be done before buying a car: turn the key without starting. If the Check Engine light did not come on with the other

A code about an internal control unit fault sounds like a bill for thousands. In reality the culprit is usually not the unit but its power supply — an

The same socket, but less data than people expect. Honestly: what reads, what does not, and why the battery's health is not checked this way.

The buyer will turn up with a cheap adapter. Better to know in advance what they will see — and why clearing codes before a sale is pointless.

Fault codes get cleared before a viewing. But some traces cannot be cleared — and those are the ones to look at.