P21D8 code meaning
Cylinder 10 Injector B Circuit/Open
Powertrain system Generic code P21xx codes Check engine light
What P21D8 means
P21D8 covers the second injector of cylinder 10, the last cylinder of a V10. No manufacturer documents this code publicly. A V10 with two injectors per cylinder is on record in the Lamborghini Huracán, whose engine combines direct and multipoint injection, yet which of them its software would call B is unknown. For comparison, Ford's eight-cylinder logic tests B circuits continuously above 11 V for 5 s, and GM's LT5 module rates an open by 200 kOhm or more with the driver off. CARB obliges makers to monitor injector output circuits whose failure can raise emissions. In practice the fault would show as a misfire on cylinder 10 (P0310) with that cylinder still fed by its other injector; the A-side equivalent would be P020A. Neighbours are P21D7 and P21D9.
P21D8 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 P21D8
- Check engine light on
- Misfire on cylinder 10 (P0310)
Common causes of P21D8
- Most likelySecond injector of cylinder 10 open internally
- PossibleWiring or connector fault at the cylinder 10 injector
- Less likelyOutput stage in the engine control module failed
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 P21D8 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. |
| D8 | The exact fault in that area. |
What to do next
- Note P21D8 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 P21D8
What does P21D8 mean?
P21D8 means "Cylinder 10 Injector B Circuit/Open". P21D8 covers the second injector of cylinder 10, the last cylinder of a V10. It is a generic code, so it means the same on every make.
Is it safe to drive with P21D8?
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 P21D8 fail an emissions test?
Yes, it can. P21D8 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 P21D8 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P21D8 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.