P21F0 code meaning
Cylinder 11 Injector B Circuit Low
Powertrain system Generic code P21xx codes Check engine light
What P21F0 means
P21F0 is reserved for a low state, typically a wire touching ground, in the B injector circuit of cylinder 11. Setting it requires at least eleven cylinders with two injectors each, so in practice a V12 or W12 with combined port and direct injection. No such engine could be confirmed: Lamborghini's V12 family uses multi-point injection only, as do Aston Martin's V12 and Mercedes-AMG's M279. Accordingly no manufacturer documents the code. If a scan tool still shows it, check the cylinder count and whether the maker uses the number for something else. The generic logic follows CARB's circuit monitoring of output components; GM's V8 shows how it is usually judged (short to ground below 0.5 Ohm with the driver off). Open circuit: P21D9; high fault: P21F1.
P21F0 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P21F0
- Check engine light on
- Misfire on cylinder 11 (P0311)
Common causes of P21F0
- Most likelyCylinder 11 B injector wire shorted to ground
- PossibleInjector with internal short to ground
- Less likelyCode read on an engine without a cylinder 11 B injector (scan tool or maker-specific use)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel injectorInjector wiringEngine control module
What each part of P21F0 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 1 | Area: fuel and air metering. |
| F0 | The exact fault in that area. |
What to do next
- Note P21F0 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P21F0
What does P21F0 mean?
P21F0 means "Cylinder 11 Injector B Circuit Low". P21F0 is reserved for a low state, typically a wire touching ground, in the B injector circuit of cylinder 11. It is a generic code, so it means the same on every make.
Is it safe to drive with P21F0?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P21F0 fail an emissions test?
Yes, it can. P21F0 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P21F0 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P21F0 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.