P020D: Cylinder 4 Injection Timing
What to do
Ask for fuel rail pressure to be checked under load before an injector is replaced. On a four-cylinder engine this cylinder sits at the end of the rail and shows a pressure shortfall before the others do — so this code is sometimes a fuel supply problem rather than an injector one, and that is a very different repair.
Mention when the fuel filter was last changed. A restricted filter starves rail pressure and is one of the cheapest things on the list.
Say whether the fault is worse under hard acceleration. A deviation that only appears under load points firmly at pressure rather than at the injector itself.
What this code means
Injection timing on cylinder 4 is not where the module commanded it to be.
On a four-cylinder engine this is the last cylinder, and it is the one at the end of the fuel rail — which gives it a failure mode the others do not have. Rail pressure is not perfectly uniform along its length. The cylinder furthest from the high pressure supply sees the pressure wave last and sees it slightly damped, so a rail that is marginally short of pressure shows itself here first.
That makes this code a useful early warning rather than merely a per-cylinder fault. Before condemning the injector, check what rail pressure is actually doing under load — a worn high pressure pump, a leaking pressure regulator or a restricted filter all produce a deviation that appears at the far end of the rail before it appears anywhere else.
The mechanism is otherwise the family's. Combustion timing is inferred from the crankshaft's instantaneous speed, so anything that weakens or delays the burn on this cylinder disturbs the same measurement — injector, compression, or glow plug.
A timing code on cylinder 4 accompanied by a rail pressure code is one fault, not two. Fix the pressure and re-check before touching an injector.
Likely causes
Start here
- Failed fuel injector · specialist
- Low fuel pressure · moderate
- Worn or leaking fuel injectors · specialist
Less common
- Injector fitted without entering its calibration code · specialist
- Low engine compression · 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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