The corrosion starts from the inner side of the metal, behind the wheel arch liner: the mud settling there and the absorbent foam seal hold the water against the metal. From outside only blistering paint shows for a long time, while underneath it can already be rusted through. The sill and the jacking point fail the same way: that already fails the roadworthiness test, and it is dangerous when changing a wheel.

The G62 sensor tells the engine control unit how hot the coolant is. If it is faulty, the control unit thinks a warm engine is cold, and runs it rich: hard warm or cold starting, a rough idle, markedly increased fuel consumption, and a dash temperature gauge that jumps around or never reaches its usual reading. The part is cheap and can be replaced in half an hour: the trouble is that many people do not recognise it and replace an injector or a lambda sensor instead. If the fault persists, the rich mixture can destroy the catalytic converter too.