P21DCCylinder 1 Injector B Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P21DC is the high-side fault of the cylinder 1 B injector: the line carries voltage where the control unit expects it to be low, typically from a short to supply or between the two injector wires. On GM's 2019 LT5 V8 the FICM injection module looks at the low side of the supplemental injector while its driver is off; less than 0.5 Ohm toward power in 20 of 25 samples sets a Type A fault, so that injector can no longer be switched. Mitsubishi's 2022 Eclipse Cross, where B is the direct high-pressure injector, needs a short circuit lasting 2 s and begins diagnosis on the negative DI line. Its manual warns against measuring the injector terminals, because the direct injection driver works with high voltage. Fail-safe, symptoms and codes P21DB (low) and P21CF (open) are closely linked.
- What you may notice
- Check engine light on
- Cylinder 1 runs weak or misfires
- Torque limited if more cylinders fail (Mitsubishi)
- Likely causes
- LikelyInjector control wire shorted to a supply wire
- PossibleBoth injector wires shorted together in the harness
- PossibleInjector coil shorted internally
- RareDriver stage of the control module damaged
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.