What it means
The control module detected an open or otherwise faulty electrical circuit for cylinder 1 injector B. The code identifies the circuit fault; it does not establish what injector B refers to on a particular engine.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine controller operates injector B on cylinder 1 and monitors its electrical circuit for the expected response. P21CF sets when that cylinder 1 injector B circuit is detected as open or otherwise electrically faulty; the code does not define what injector B represents on every engine.
Common causes
Most likely first.
- Open or damaged wiring
- Loose or corroded injector connector
- Injector electrical fault
Symptoms
- Check-engine light
- Rough idle or engine vibration
- Engine hesitation or reduced power
- Misfire, especially under load
How to diagnose it
- Save freeze-frame data and check cylinder-specific misfire data and related injector codes to see when cylinder 1 began running unevenly.
- Identify cylinder 1 and injector B using the vehicle's service information, then inspect that injector's connector and wiring for disconnection, corrosion, chafing, or heat damage.
- Check that the injector B connector is fully seated and inspect its terminals for bent, spread, or pushed-back pins.
- With the correct wiring information, test the cylinder 1 injector B circuit for continuity and shorts using the manufacturer's procedure.
- Test the injector's electrical operation against the manufacturer's specification and compare with other injectors only where the service procedure allows.
Common fixes
- Reconnect and secure the cylinder 1 injector B connector.
- Repair damaged or open wiring in the cylinder 1 injector B circuit.
- Clean or repair corroded or damaged connector terminals.
- Replace cylinder 1 injector B if its electrical fault is confirmed.
Can I keep driving?
If the engine is misfiring or shaking, avoid driving under load because continued misfire can damage the catalytic converter and reduce power. If it runs smoothly, keep trips short and have the cylinder 1 injector B circuit repaired soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.