P21DB code meaning
Cylinder 1 Injector B Circuit Low
Powertrain system Generic code P21xx codes Check engine light
What P21DB means
P21DB means the drive circuit of the B injector on cylinder 1 is pulled toward ground. Two makers document it, with opposite meanings of B. Mitsubishi's 2022 Eclipse Cross uses B for the direct high-pressure injector (its port injector faults are P0261 ff.) and sets P21DB when an interruption or a grounded line persists for 2 s with 10 to 16.5 V battery and over 10 V on the injector driver supply. One faulty cylinder loses both its injectors; with several faults direct injection is switched off and the engine runs on port injection with limited torque. GM's 2019 LT5 V8 tests the low side of its supplemental B injector with the driver off: below 0.5 Ohm to ground in 20 of 25 samples, Type A. Ford covers B faults only with P21CF to P21D6, opens and shorts together. P21DC is the high counterpart, P21CF the open circuit.
P21DB at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P21DB
- Check engine light on
- Cylinder 1 misfire or shut-off
- Reduced torque when several cylinders are affected (Mitsubishi)
Common causes of P21DB
- Most likelyInjector wire chafed through to ground
- PossibleInjector winding open or shorted to its housing
- PossibleDamaged intermediate or injector connector
- Less likelyEngine or injection control module faulty
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 P21DB 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. |
| DB | The exact fault in that area. |
What to do next
- Note P21DB 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 P21DB
What does P21DB mean?
P21DB means "Cylinder 1 Injector B Circuit Low". P21DB means the drive circuit of the B injector on cylinder 1 is pulled toward ground. It is a generic code, so it means the same on every make.
Is it safe to drive with P21DB?
Drive gently and only to a workshop. With P21DB the car can go into limp mode (reduced power) to protect itself.
Will P21DB fail an emissions test?
Yes, it can. P21DB 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 P21DB to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P21DB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.