OBD Cylinder 10 Injector B Circuit/Open
What it means
P21D8 stands for Cylinder 10 Injector B Circuit/Open. P21D8 is a P code, so the fault sits in the engine, transmission and emissions systems. For P21D8, the second digit places it in fuel and air metering. For P21D8, work through the cause list below, cheapest checks first.
Where it lives
For P21D8, the injector sits on the circuit this code reports. The description of P21D8 puts it on cylinder 10.
What to check first
For P21D8, pull the connector and inspect the terminals for spread, corrosion or backed-out pins before testing anything else.
Check these first
- P21D8: Faulty or contaminated sensor in the fuel/air metering circuit
- P21D8: Damaged or shorted wiring or connector for the affected circuit
- P21D8: Vacuum leak or intake system restriction
- P21D8: Failing fuel pump, injector, or fuel pressure regulator
What to do next
P21D8 reports from the fuel and air metering system. These steps cover P21D8 in general, and the exact cause on your vehicle can differ from the cause named above.
- P21D8: Read freeze frame data and related codes with an OBD-II scanner
- P21D8: Inspect the affected sensor wiring and connector for damage
- P21D8: Compare live sensor readings (fuel trim, airflow, temperatures) to manufacturer specs
- P21D8: Smoke test the intake system if lean or vacuum conditions are suspected
- P21D8: Replace the failed component after confirming it with live data
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.