P21F0: Cylinder 11 Injector B Circuit Low

What does P21F0 mean?

P21F0 is reserved for a low state, typically a wire touching ground, in the B injector circuit of cylinder 11. Setting it requires at least eleven cylinders with two injectors each, so in practice a V12 or W12 with combined port and direct injection. No such engine could be confirmed: Lamborghini's V12 family uses multi-point injection only, as do Aston Martin's V12 and Mercedes-AMG's M279. Accordingly no manufacturer documents the code. If a scan tool still shows it, check the cylinder count and whether the maker uses the number for something else. The generic logic follows CARB's circuit monitoring of output components; GM's V8 shows how it is usually judged (short to ground below 0.5 Ohm with the driver off). Open circuit: P21D9; high fault: P21F1.

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

Symptoms

• Check engine light on
• Misfire on cylinder 11 (P0311)

Common causes

• High Cylinder 11 B injector wire shorted to ground
• Medium Injector with internal short to ground
• Low Code read on an engine without a cylinder 11 B injector (scan tool or maker-specific use)

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