P21D4 code meaning
Cylinder 6 Injector B Circuit/Open
Powertrain system Generic code P21xx codes Check engine light
What P21D4 means
P21D4 is the last B injector code on a six-cylinder engine. Ford's second-generation 2.7 and 3.5 EcoBoost V6 combine port and direct injection, label the port injectors B and test this circuit together with P21CF to P21D3, continuously above 11 V within 5 s; on these engines cylinder 6 is the rear cylinder of the second bank. On the 3.5 the direct system is shut down at low speed and light load and the engine runs on port fuel alone, so an open cylinder 6 port injector is most noticeable at idle and in gentle driving. GM's 2019 LT5 V8 also covers cylinder 6 in its injection module, Type A after 20 of 25 failed samples. The A-side direct injector code is P0206, the misfire code P0306; P21E6 and P21E7 are the low and high faults.
P21D4 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 3.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P21D4
- Check engine light on
- Misfire on cylinder 6 (P0306)
- Slightly rough idle
Common causes of P21D4
- Most likelyPort injector of cylinder 6 open internally
- PossibleDamaged wire at the rear of the engine, hard to inspect
- PossibleConnector not fully latched after earlier work on the intake
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 P21D4 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. |
| D4 | The exact fault in that area. |
What to do next
- Note P21D4 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 P21D4
What does P21D4 mean?
P21D4 means "Cylinder 6 Injector B Circuit/Open". P21D4 is the last B injector code on a six-cylinder engine. It is a generic code, so it means the same on every make.
Is it safe to drive with P21D4?
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 P21D4 fail an emissions test?
Yes, it can. P21D4 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 P21D4 to fix?
Difficulty: medium. A typical repair takes 1 to 3.5 hours of work. This is a job for a workshop.
Will P21D4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.