Powertrain, generic (extended)

P21DC Cylinder 1 Injector B Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Injector control wire shorted to a supply wire
Both injector wires shorted together in the harness
Injector coil shorted internally
Driver stage of the control module damaged

Symptoms

  • Check engine light on
  • Cylinder 1 runs weak or misfires
  • Torque limited if more cylinders fail (Mitsubishi)

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–900
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injectorinjector wiringengine control module

Related codes

P21DBP21CFP0262P21DFP0301

References: mitsubishitechinfo.com, gsi.ext.gm.com, mitsubishitechinfo.com.