Engine

Low-end pull has gone, the diesel started smoking and the idle turned rough — and there is an intake runner code on the list. Nine times out of ten th

The red oil can lit up, or the scanner returned P0521 — and you have a second to decide whether the sensor is lying or the engine really has no pressu

The car has lost power, or jerks under acceleration. What a scanner shows here — and what you still have to check by hand.

Lost power, higher fuel use, and a quieter engine under load? That is what a car looks like when it can no longer hear knock.

The unit uses it to judge how much air enters the engine. It lies quietly: the car drives, but fuel use rises and power fades.

The car jerks pulling away, the revs live their own life, the pedal answers late. One reading on screen tells whether the throttle is to blame.

A diesel has its own codes, its own live data and its own order of checks. Half the familiar petrol habits simply do not apply.

The part was replaced, the code cleared, and a week later the light is on again. Five causes in order of frequency, and how to tell them apart.

The code sounds worse than it is in half the cases. But it must be checked before you drive on.