OBD Cylinder 9 Injector B Circuit Low
What it means
P21EC stands for Cylinder 9 Injector B Circuit Low. P21EC is a P code, so the fault sits in the engine, transmission and emissions systems. For P21EC, the second digit places it in fuel and air metering. For P21EC, work through the cause list below, cheapest checks first.
Where it lives
For P21EC, the injector sits on the circuit this code reports. The description of P21EC puts it on cylinder 9.
What to check first
For P21EC, pull the connector and inspect the terminals for spread, corrosion or backed-out pins before testing anything else.
Check these first
- P21EC: Faulty or contaminated sensor in the fuel/air metering circuit
- P21EC: Damaged or shorted wiring or connector for the affected circuit
- P21EC: Vacuum leak or intake system restriction
- P21EC: Failing fuel pump, injector, or fuel pressure regulator
What to do next
P21EC is a fault in the fuel and air metering system. The steps below are general, so what actually failed on your vehicle may not be what P21EC names.
- P21EC: Read freeze frame data and related codes with an OBD-II scanner
- P21EC: Inspect the affected sensor wiring and connector for damage
- P21EC: Compare live sensor readings (fuel trim, airflow, temperatures) to manufacturer specs
- P21EC: Smoke test the intake system if lean or vacuum conditions are suspected
- P21EC: Replace the failed component after confirming it with live data
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.