P21EF: Cylinder 10 Injector B Circuit High

What does P21EF mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

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

Common causes

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

Likelihood is a general estimate across vehicles; your make and model may differ.