P21D8: Cylinder 10 Injector B Circuit/Open

What does P21D8 mean?

P21D8 covers the second injector of cylinder 10, the last cylinder of a V10. No manufacturer documents this code publicly. A V10 with two injectors per cylinder is on record in the Lamborghini Huracán, whose engine combines direct and multipoint injection, yet which of them its software would call B is unknown. For comparison, Ford's eight-cylinder logic tests B circuits continuously above 11 V for 5 s, and GM's LT5 module rates an open by 200 kOhm or more with the driver off. CARB obliges makers to monitor injector output circuits whose failure can raise emissions. In practice the fault would show as a misfire on cylinder 10 (P0310) with that cylinder still fed by its other injector; the A-side equivalent would be P020A. Neighbours are P21D7 and P21D9.

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

Symptoms

• Check engine light on
• Misfire on cylinder 10 (P0310)

Common causes

• High Second injector of cylinder 10 open internally
• Medium Wiring or connector fault at the cylinder 10 injector
• Low Output stage in the engine control module failed

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