Powertrain, generic (extended)

P21DB Cylinder 1 Injector B Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Injector wire chafed through to ground
Injector winding open or shorted to its housing
Damaged intermediate or injector connector
Engine or injection control module faulty

Symptoms

  • Check engine light on
  • Cylinder 1 misfire or shut-off
  • Reduced torque when several cylinders are affected (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

P21DCP21CFP0261P0262P21DEP0301

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