P02D3: Cylinder 4 Fuel Injector A Offset Learning At Max Limit
What to do
Ask for the high pressure fuel pipe to this injector to be inspected. This cylinder is at the end of the rail, and a restricted or damaged supply pipe makes the injector under-deliver while being perfectly good itself.
If a pipe is disturbed or replaced, it must be a new one. These pipes seal by deforming at the cone and a reused one is a known cause of leaks and restrictions — worth confirming with the garage.
Ask whether another cylinder has an opposite fault stored. Two injectors carrying each other's calibration codes push the trims to opposite limits, and that is a coding correction rather than a repair.
Mention the fuel filter's age and any history of poor fuel.
What this code means
The correction the module applies to cylinder 4's injector has reached the top of its adjustment range.
Cylinder 4 under-delivers and the module has added all the correction it can.
At the end of the rail, under-delivery has a supply explanation the other cylinders rarely have. If the feed to this injector is restricted — a kinked or corroded high pressure pipe, a partially blocked union, or debris caught at the rail outlet — the injector opens exactly as commanded and less fuel arrives to pass through it. The injector is faultless.
That is worth eliminating because it is cheap and visible. High pressure pipes are inspected and replaced routinely, and they are frequently disturbed by other work in that area.
Beyond supply, the ordinary under-delivery causes apply: a nozzle narrowed by deposits, a slow-opening actuator, or a calibration code that does not describe the injector actually fitted.
On any engine where this appears together with a minimum-limit code on another cylinder, check the calibration codes first. Two injectors carrying each other's codes drive their trims to opposite ends, and there is nothing mechanically wrong to find.
Note that a pipe replaced on a common rail system must be a new one. These pipes seal by deformation at the cone, and refitting a used pipe is a well-known route to a leak or a restriction.
Likely causes
Start here
- Blocked or restricted injector nozzle · specialist
- Contaminated or poor quality fuel · moderate
Less common
- Restricted high pressure fuel pipe · moderate
- Injector fitted without entering its calibration code · 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.
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