P21D6 code meaning
Cylinder 8 Injector B Circuit/Open
Powertrain system Generic code P21xx codes Check engine light
What P21D6 means
P21D6 is the highest B injector code that any manufacturer documents publicly: both Ford's port injector check (P21CF to P21D6) and GM's LT5 injection module list end here. On the LT5 the port injectors exist to add fuel under boost beyond what the direct system and its mechanical pump can deliver, so an open cylinder 8 injector shows up mainly at high load, where that cylinder can run lean and lose power; GM stores the fault as Type A from 20 failed samples out of 25 with at least 11 V on the powertrain relay. In GM's firing order cylinder 8 follows cylinder 1. On Ford's 5.0 V8 from 2018 it is the rear cylinder of the second bank and the check runs continuously for 5 s. The direct injector counterpart is P0208; P21D5 is cylinder 7.
P21D6 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P21D6
- Check engine light on
- Misfire or lean running on cylinder 8 under load
- Power loss at wide-open throttle
Common causes of P21D6
- Most likelyPort injector of cylinder 8 open
- PossibleWire damage at the rear of the engine near the firewall
- Less likelyOutput of the engine or separate injection 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 P21D6 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. |
| D6 | The exact fault in that area. |
What to do next
- Note P21D6 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 P21D6
What does P21D6 mean?
P21D6 means "Cylinder 8 Injector B Circuit/Open". P21D6 is the highest B injector code that any manufacturer documents publicly: both Ford's port injector check (P21CF to P21D6) and GM's LT5 injection module list end here. It is a generic code, so it means the same on every make.
Is it safe to drive with P21D6?
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 P21D6 fail an emissions test?
Yes, it can. P21D6 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 P21D6 to fix?
Difficulty: medium. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P21D6 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.