OBD Fuel Control System B Too Rich at Idle Bank 2
What it means
P21FB stands for Fuel Control System B Too Rich at Idle Bank 2. P21FB is a P code, so the fault sits in the engine, transmission and emissions systems. For P21FB, the second digit places it in fuel and air metering. For P21FB, work through the cause list below, cheapest checks first.
What to check first
For P21FB, compare the reading on bank 2 against the other bank on the same scan tool, because a bank that reads differently from its twin is the fault.
Check these first
- P21FB: Faulty or contaminated sensor in the fuel/air metering circuit
- P21FB: Damaged or shorted wiring or connector for the affected circuit
- P21FB: Vacuum leak or intake system restriction
- P21FB: Failing fuel pump, injector, or fuel pressure regulator
What to do next
P21FB belongs to the fuel and air metering system. These are the general steps for P21FB, and the exact cause on your vehicle can differ.
- P21FB: Read freeze frame data and related codes with an OBD-II scanner
- P21FB: Inspect the affected sensor wiring and connector for damage
- P21FB: Compare live sensor readings (fuel trim, airflow, temperatures) to manufacturer specs
- P21FB: Smoke test the intake system if lean or vacuum conditions are suspected
- P21FB: Replace the failed component after confirming it with live data
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.