What it means
The control module detected an open or otherwise faulty electrical circuit for cylinder 5 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 control module monitors the electrical path that operates injector B for cylinder 5. It sets P21D3 when that path appears open or electrically faulty, so the injector may not deliver its commanded fuel even though the code alone does not identify what “B” means on this engine.
Common causes
Most likely first.
- Open or damaged wiring
- Loose or corroded injector connector
- Injector electrical fault
Symptoms
- Check-engine light on
- Rough running or misfire
- Reduced engine power
- Increased fuel consumption
How to diagnose it
- Record freeze-frame data and check for related injector or misfire codes to see when the cylinder 5 injector B fault occurred.
- Use vehicle service information to identify cylinder 5 and injector B, then inspect that injector’s connector and nearby wiring for looseness, corrosion, damage, or chafing.
- With the ignition off, disconnect and reconnect the cylinder 5 injector B connector and check whether its terminals are pushed back, spread, or contaminated.
- Compare the injector B circuit readings at cylinder 5 with the manufacturer's specification and, where appropriate, the equivalent injector circuit on another cylinder.
- If wiring continuity and connections are sound, test the cylinder 5 injector B electrically to determine whether the injector itself is open or otherwise faulty.
Common fixes
- Secure the cylinder 5 injector B connector and clean or repair corroded terminals.
- Repair damaged or open wiring in the cylinder 5 injector B circuit.
- Replace the cylinder 5 injector B if it fails electrical testing.
Can I keep driving?
If the engine runs smoothly and the warning light is steady, limit driving and arrange prompt diagnosis; a cylinder 5 fueling fault can increase emissions and fuel use. Avoid hard acceleration, and stop driving if the light flashes, the engine shakes badly, or power drops sharply.
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.