Powertrain, generic (extended)

P21F3 Cylinder 12 Injector B Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P21F3 ends the B injector series of SAE J2012: a high signal on the cylinder 12 circuit, caused by a short to supply on the switched side. The series runs from P21CF to P21DA for opens and from P21DB to P21F3 for low/high pairs; the A injector equivalent here is P0295. Public manufacturer documents only reach cylinder 8 (GM's LT5 V8) or cylinder 4 (Mitsubishi), and no twelve-cylinder with dual injection could be documented, since Lamborghini's and Aston Martin's V12s use port injection alone. Should the code appear, the injector cannot open; cylinder 12 then relies on its other injector, and the driver stage takes the brunt of each switching attempt. GM's criteria for the same fault type serve as a guide: within 0.5 Ohm of power with the driver off. Low fault: P21F2.

Likely causes

Control wire of the cylinder 12 B injector shorted to supply
Injector coil with shorted windings
Driver stage damaged by a lasting short

Symptoms

  • Check engine light on
  • Cylinder 12 lean or misfiring (P0312)

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,200
Time1–5 h

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

Parts involved

fuel injectorinjector wiringengine control module

Related codes

P21F2P21DAP0295P21F1P0312

References: law.cornell.edu, gsi.ext.gm.com, en.wikipedia.org, mitsubishitechinfo.com.