Powertrain, generic (extended)

P21EF Cylinder 10 Injector B Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P21EF stands for a high reading on the B injector circuit of cylinder 10. No public manufacturer document covers it, so the exact threshold is unknown; the closest documented model is GM's LT5 V8, where a switched-off low side within 0.5 Ohm of supply counts as a short and sets a Type A fault. A vehicle needs ten or more cylinders and two injectors each to use the code, which so far is documented only for Lamborghini's V10 in the Huracán. A short to power keeps the injector from ever opening, and switching against it strains the output stage, which may need replacement if the fault persisted. When P21EF shows up together with other high codes on the same bank, look for a common supply or connector. Low fault: P21EE; A injector high fault: P0289.

Likely causes

Cylinder 10 B injector control wire touching a live circuit
Short inside a connector shared by several injectors
Injector coil shorted
Output stage overloaded by the short

Symptoms

  • Check engine light on
  • Cylinder 10 weak or misfiring under load
  • Lean mixture on the second bank

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

P21EEP21D8P0289P21EDP21F1P0310

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