What are the common causes of P21CF?

An open circuit in the cylinder 1 injector B wiring. Corrosion or damage at the cylinder 1 injector B connector. A failing cylinder 1 injector B. Low fuel pressure feeding the cylinder 1 injector. A failing ECM driver for the cylinder 1 injector B.

Check the cylinder 1 injector B wiring for opens. Inspect the cylinder 1 injector B connector for corrosion. Measure resistance through the cylinder 1 injector B. Check fuel pressure feeding the injector. Replace the cylinder 1 injector B if it does not fire. Clear the code and retest.

P21CF

Cylinder 1 Injector B Circuit/Open

System: Fuel and air metering (P code)
Lamp: Check Engine Light
Category: Powertrain - Fuel/Air Metering

What it means

P21CF means Cylinder 1 Injector B Circuit/Open.

Where it lives

For P21CF, the circuit described runs through the injector. The description of P21CF puts it on cylinder 1.

Check these first

An open circuit in the cylinder 1 injector B wiring
Corrosion or damage at the cylinder 1 injector B connector
A failing cylinder 1 injector B
Low fuel pressure feeding the cylinder 1 injector
A failing ECM driver for the cylinder 1 injector B

What to do next

Check the cylinder 1 injector B wiring for opens
Inspect the cylinder 1 injector B connector for corrosion
Measure resistance through the cylinder 1 injector B
Check fuel pressure feeding the injector
Replace the cylinder 1 injector B if it does not fire
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.