What it means
The control module detected a high electrical signal in the cylinder 4 injector B circuit. This indicates an electrical circuit condition; it does not by itself establish injector flow or cylinder fuel balance.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Injector B is the second injector circuit identified for cylinder 4 by the control system; this code concerns its electrical signal, not a confirmed fuel-flow fault. The control module sets P21E3 when the signal is higher than expected, which can be caused by a short to voltage, a damaged connector, or an injector electrical fault.
Common causes
Most likely first.
- Short to voltage in wiring
- Damaged or corroded connector
- Injector electrical fault
Symptoms
- Check-engine light on
- Rough running or misfire
- Reduced engine power
- Increased fuel consumption
How to diagnose it
- Save freeze-frame data and check for cylinder 4 misfire or related injector codes to identify when the high signal was detected.
- Inspect the cylinder 4 injector B connector and harness for exposed wire, corrosion, loose terminals, or contact with a powered circuit.
- Use the vehicle wiring information to locate the circuit and check for a short to voltage, following the manufacturer’s isolation procedure.
- With the injector disconnected as directed, check the harness for unintended voltage, poor terminal fit, and continuity.
- Test injector B for cylinder 4 against the manufacturer’s electrical specification.
Common fixes
- Secure the cylinder 4 injector B connector and clean or replace corroded terminals.
- Repair wiring with damaged insulation or a short to voltage in the circuit.
- Replace a connector or terminal that is damaged or cannot retain its pin properly.
- Replace injector B for cylinder 4 if its electrical test confirms an internal fault.
Can I keep driving?
If the engine misfires or loses power, reduce load and arrange repair promptly because continued misfiring can damage the catalytic converter and increase emissions. Stop driving if the warning light flashes or the engine runs severely unevenly.
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.