P21EF code meaning
Cylinder 10 Injector B Circuit High
Powertrain system Generic code P21xx codes Check engine light
What P21EF means
P21EF stands for a high reading on the B injector circuit of cylinder 10. No public manufacturer document covers it, so the exact threshold is unknown; the closest documented model is GM's LT5 V8, where a switched-off low side within 0.5 Ohm of supply counts as a short and sets a Type A fault. A vehicle needs ten or more cylinders and two injectors each to use the code, which so far is documented only for Lamborghini's V10 in the Huracán. A short to power keeps the injector from ever opening, and switching against it strains the output stage, which may need replacement if the fault persisted. When P21EF shows up together with other high codes on the same bank, look for a common supply or connector. Low fault: P21EE; A injector high fault: P0289.
P21EF 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 P21EF
- Check engine light on
- Cylinder 10 weak or misfiring under load
- Lean mixture on the second bank
Common causes of P21EF
- Most likelyCylinder 10 B injector control wire touching a live circuit
- PossibleShort inside a connector shared by several injectors
- PossibleInjector coil shorted
- Less likelyOutput stage overloaded by the short
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 P21EF 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. |
| EF | The exact fault in that area. |
What to do next
- Note P21EF 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 P21EF
What does P21EF mean?
P21EF means "Cylinder 10 Injector B Circuit High". P21EF stands for a high reading on the B injector circuit of cylinder 10. It is a generic code, so it means the same on every make.
Is it safe to drive with P21EF?
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 P21EF fail an emissions test?
Yes, it can. P21EF 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 P21EF to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P21EF clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.