P01D2: Cylinder 4 Injection Timing Performance - Over Advanced
What to do
Ask for fuel rail pressure to be checked before this injector is replaced. On a four-cylinder engine this is the cylinder at the end of the rail, where pressure waves collect — and a pressure control fault advances its combustion without the injector being at fault.
Ask whether any fuel pressure codes are stored alongside, since those would very likely be the same fault.
Say whether the engine knocks or sounds harsh under load, which fits this and helps confirm it.
Do not leave it running like this, because early combustion loads the piston and bearings at the wrong point in the stroke.
What this code means
Combustion on cylinder 4 is happening earlier than the module commanded.
On a four-cylinder engine this is the cylinder at the end of the fuel rail, and that position produces over-advance by a route the other cylinders do not have.
Rail pressure is not constant along its length. Each injector opening sends a pressure wave down the rail, and those waves reflect off the closed end — where cylinder 4 sits. A reflected wave arriving as this injector opens raises the pressure it sees above what the module assumed, and fuel injected at higher pressure atomises finer, ignites sooner, and advances the burn.
This is why rail pressure control deserves examining before the injector is condemned. A pressure regulator that is slow to respond, or a rail damper that has failed, exaggerates those waves — and the cylinder at the end of the rail feels it first and worst.
A rail pressure code stored alongside this one is very probably the same fault. Repair that and re-check before ordering an injector.
Where pressure control is sound, the ordinary causes apply: a leaking injector delivering fuel before its commanded opening, an inaccurate pilot injection, or fuel more volatile than diesel.
The direction still carries the family's urgency. Early combustion works against the crank and loads the piston at the wrong angle, so this is a repair rather than an observation.
Likely causes
Start here
- Worn or leaking fuel injectors · specialist
Less common
- Stuck fuel pressure regulator · moderate
- Faulty fuel rail pressure sensor · moderate
- Contaminated or poor quality fuel · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P01D2.