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.
What to check
- Warm it up and watch the dash temperature gauge: the needle should sit steadily at the middle reading, not jump around
- Watch a cold start, then a warm start after twenty minutes standing
- With a code reader look for the 17664 / P1256 code in the engine control unit
