What it means
The control module detected a low electrical signal in the cylinder 11 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 11 injector B is the injector identified for cylinder 11, and its driver circuit carries the electrical command that operates it. The control module monitors the response on this circuit and sets P21F0 when the signal is lower than expected. This is a low-signal electrical fault in the cylinder 11 injector B circuit; it does not by itself indicate injector flow or fuel balance.
Common causes
Most likely first.
- Short to ground 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 review live misfire counts and fuel trims to see when the cylinder 11 injector B circuit fault appears and whether cylinder 11 is misfiring.
- With the engine off, inspect the cylinder 11 injector B connector and harness for corrosion, loose terminals, chafing, or insulation damage that could allow contact with ground.
- Use the wiring diagram to check the cylinder 11 injector B circuit for a short to ground, an open, or a poor connection.
- With the circuit isolated according to the manufacturer's procedure, test the injector’s electrical condition against the manufacturer's specification.
- If the injector and wiring pass, test the cylinder 11 injector B driver circuit at the control module following the manufacturer's procedure.
Common fixes
- Clean and secure a corroded or loose cylinder 11 injector B connector.
- Repair a short to ground, open, or damaged wire in the cylinder 11 injector B circuit.
- Replace cylinder 11 injector B if its electrical test is outside the manufacturer's specification.
- Repair or replace the control module only if its cylinder 11 injector B driver fails the specified tests.
Can I keep driving?
If the engine runs smoothly and the warning light is steady, avoid heavy acceleration and limit driving until the fault is diagnosed. Stop if the light flashes, the engine misfires badly, or power drops substantially, because continued 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.