What it means
The control module detected an open or otherwise faulty electrical circuit for cylinder 3 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 3 and monitors its electrical circuit for the expected response. P21D1 sets when the cylinder 3 injector B circuit is detected as open or otherwise electrically faulty; the code alone does not establish what injector B refers to on a particular 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 review cylinder-specific misfire counts and related injector codes to see when cylinder 3 was affected.
- Identify cylinder 3 and injector B from vehicle service information, then inspect that injector's wiring and connector for damage, corrosion, or disconnection.
- Check the connector terminals for poor contact, including pins that are bent, spread, or pushed back.
- Test the cylinder 3 injector B circuit for continuity and shorts using the vehicle wiring diagram and manufacturer's procedure.
- Measure the injector's electrical operation against the manufacturer's specification to distinguish an injector fault from a harness fault.
Common fixes
- Reconnect and secure the cylinder 3 injector B connector.
- Repair damaged or open wiring in the cylinder 3 injector B circuit.
- Clean or repair corroded or damaged connector terminals.
- Replace cylinder 3 injector B if its electrical fault is confirmed.
Can I keep driving?
If the engine is shaking or misfiring, avoid load and extended driving because the resulting misfire can damage the catalytic converter. If it runs normally, keep driving limited and have the cylinder 3 injector B circuit checked promptly.
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.