P01CC: Cylinder 1 Injection Timing Performance - Over Advanced
What to do
Take this one more seriously than a rough idle usually deserves. Fuel burning too early pushes against the engine instead of driving it, and left alone it can damage the piston and bearings on that cylinder.
Say whether the engine sounds harsh, knocking or rattly under load. That fits this fault and helps confirm it.
Be asked, and answer honestly, whether the car may have been misfuelled — even a small amount of petrol in a diesel tank makes the fuel ignite earlier than intended and produces exactly this. It is common, it is fixable, and hiding it only costs money.
Mention any recent injector work. A worn or leaking injector dribbling fuel in early is the most frequent cause.
What this code means
Combustion on cylinder 1 is happening earlier than the module commanded.
Over advanced is the rarer and more damaging of the two directions, and it deserves more urgency than its retarded sibling. Fuel burning before the piston has reached the top of its stroke works against the crankshaft rather than with it — the pressure rise opposes the motion, which is heard as diesel knock and felt as harshness.
Sustained over-advance is genuinely destructive. Peak cylinder pressure arrives at the wrong crank angle, and the load lands on the piston crown, the gudgeon pin and the big end bearing. This is a fault to repair rather than to monitor.
The causes are a shorter list than the retarded case.
- An injector leaking before its commanded opening, dribbling fuel into the cylinder early. This is the commonest cause and it is a worn injector.
- Fuel with an unusually high cetane number, or contaminated with something more volatile — petrol in a diesel tank being the obvious case — which ignites sooner than the strategy expects.
- Excessive compression or hot spots, from carbon build-up or an overheating cylinder, which ignite the charge before the burn was scheduled.
A timing reference error moves every cylinder together, so a single-cylinder over-advance is not a chain or crank sensor fault. That distinction narrows this to the injector or that cylinder's condition.
Misfuelling is worth asking about directly, because it is common, it produces exactly this, and it will not be volunteered.
Likely causes
Start here
- Worn or leaking fuel injectors · specialist
Less common
- Contaminated or poor quality fuel · moderate
- Carbon deposits in the combustion chamber · specialist
- Failed fuel injector · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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