What it means
The control module detected a high electrical signal in the cylinder 10 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
Cylinder 10 injector B is the injector identified for cylinder 10, and its driver circuit carries the electrical command that operates it. The control module monitors the circuit response and sets P21EF when the signal is higher than expected. This points to an electrical fault such as a short to voltage in the cylinder 10 injector B circuit; it does not confirm a fuel-flow problem.
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
- Record freeze-frame data and check live misfire counts and fuel trims to determine when the cylinder 10 injector B circuit fault occurs and whether cylinder 10 is misfiring.
- With the engine off, inspect the cylinder 10 injector B connector and nearby harness for corrosion, loose pins, chafing, heat damage, or contact with a power source.
- Use the wiring diagram to check the cylinder 10 injector B circuit for a short to voltage, an open, or a poor connection to the control module.
- Isolate the circuit as specified by the manufacturer and test the injector’s electrical condition against the manufacturer's specification; check whether the high signal persists when it is disconnected.
- If the wiring and injector pass, test the cylinder 10 injector B driver circuit at the control module using the manufacturer's procedure.
Common fixes
- Clean and secure a corroded or loose cylinder 10 injector B connector.
- Repair wiring shorted to voltage or damaged in the cylinder 10 injector B circuit.
- Replace cylinder 10 injector B if its electrical test is outside the manufacturer's specification.
- Repair or replace the control module only if its cylinder 10 injector B driver fails the specified tests.
Can I keep driving?
If the engine runs normally and the warning light stays steady, keep driving limited and avoid heavy loads until the circuit is repaired. Stop if the light flashes, the engine misfires severely, or power falls sharply, as sustained misfire can damage the catalytic converter.
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.