P02F1: Cylinder 4 Injector Circuit Range/Performance
What to do
Ask for a voltage drop test on the injector wiring rather than just a continuity check. They are not the same thing — a circuit can show perfect continuity and still lose too much voltage when it actually carries current, and that is the commonest cause of this fault on the last cylinder of the harness.
Ask for the connector at the module end to be checked too, not only the one at the injector. Everything in that run adds up.
Expect rough running and possibly reduced power.
Get it repaired reasonably promptly. A cylinder that is not firing correctly sends unburnt fuel into the exhaust, and that can damage the catalytic converter or particulate filter — a far larger bill than the fault itself.
What this code means
The electrical behaviour of cylinder 4's injector circuit is wrong, without being open or short.
The module drives the injector and reads the current waveform back; cylinder 4's is valid but not the shape a healthy injector produces.
On a four-cylinder engine this is the last cylinder, and it is usually the far end of the injector harness — which gives it the family's most ordinary cause. Every connection between the module and this injector is in series with it, so it accumulates whatever resistance the whole run has picked up: the module connector, any intermediate joint, the loom branch, and its own plug.
A voltage drop test along that run finds this quickly, and a continuity test does not. Continuity confirms a path exists; it says nothing about how much voltage that path loses when real current flows, and injector drive current is substantial. That distinction is the whole test.
This is the same failure mode as a corroded battery terminal that cranks fine until it is cold. The circuit works until it is asked to carry current.
Where the wiring is sound, the injector itself is the answer — a degraded winding or piezo stack genuinely changes the electrical characteristic, and on a high-mileage engine that is an honest outcome rather than a last resort.
Check for an injector control module if the engine has one, since a failing drive stage there produces this on the cylinder it serves.
Likely causes
Start here
- Corroded or loose connector · easy
- Failed fuel injector · specialist
Less common
- Damaged wiring harness · moderate
- Open circuit in injector wiring · moderate
Rare
- Failed injector control module · specialist
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.
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