What it means
The control module detected a low electrical signal in the cylinder 7 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 7 injector B is the injector identified for cylinder 7, and its driver circuit carries the electrical command that operates it. The control module monitors the circuit response and sets P21E8 when the signal is lower than expected. This points to an electrical fault in the cylinder 7 injector B circuit; it does not establish 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 check live misfire counts and fuel trims to determine when the cylinder 7 injector B circuit fault appears and whether cylinder 7 is misfiring.
- With the engine off, inspect the cylinder 7 injector B connector and harness for corrosion, loose terminals, chafing, or a wire touching ground.
- Use the wiring diagram to check the circuit from cylinder 7 injector B to the control module for a short to ground, damaged conductor, or poor connection.
- With the circuit isolated according to the manufacturer's procedure, test the injector’s electrical condition and compare it with the manufacturer's specification.
- If the harness and injector pass, test the cylinder 7 injector B driver circuit at the control module using the manufacturer's diagnostic procedure.
Common fixes
- Clean and secure a corroded or loose cylinder 7 injector B connector.
- Repair a short to ground or damaged wire in the cylinder 7 injector B circuit.
- Replace cylinder 7 injector B if its electrical test is outside the manufacturer's specification.
- Repair or replace the control module only if its cylinder 7 injector B driver fails the specified tests.
Can I keep driving?
If the engine runs smoothly and the warning light is steady, keep any trip short and avoid heavy loads until the fault is diagnosed. Stop driving if the light flashes, the engine runs very rough, or power falls significantly, because a resulting 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.