P21F2: Cylinder 12 Injector B Circuit Low

What does P21F2 mean?

P21F2 is the generic code for a low circuit state, usually a grounded control wire, at the B injector of cylinder 12. It would need a twelve-cylinder engine with two injectors per cylinder, and none could be documented: the V12s from Lamborghini and Aston Martin inject into the ports only. No manufacturer publishes the code in this sense. One maker does use the number differently: McLaren bulletin KA-01931 lists P21F205 and P21F22F on the Artura, a V6 plug-in hybrid, as high-voltage battery faults (safety design current too low/high), repaired by replacing battery parts. On an Artura it is therefore a battery fault, not an injector fault. For a genuine injector fault, CARB's circuit monitoring applies, and GM's V8 criteria (ground short below 0.5 Ohm) are a guide. High fault: P21F3.

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

Symptoms

• Check engine light on
• Misfire on cylinder 12 (P0312)
• Hybrid warning instead, if the code is a McLaren battery fault

Common causes

• High Cylinder 12 B injector wire shorted to ground
• Medium Injector with internal ground fault
• Low Manufacturer-specific use of the number (McLaren Artura high-voltage battery)

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