What it means
The control module detected a low electrical signal in the cylinder 8 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 8 injector B is the injector identified for cylinder 8, and its driver circuit provides the electrical command for injector operation. The control module monitors this circuit and sets P21EA when its signal is lower than expected. The low reading indicates an electrical fault in the cylinder 8 injector B circuit, not a confirmed fuel-flow problem.
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
- Record freeze-frame data and review live misfire counts and fuel trims to see when the cylinder 8 injector B circuit fault occurs and whether cylinder 8 is affected.
- With the engine off, inspect the cylinder 8 injector B connector and harness for corrosion, loose terminals, damaged insulation, or wires contacting ground.
- Use the vehicle wiring diagram to check the cylinder 8 injector B circuit for a short to ground, an open, or excessive connection resistance.
- With the circuit isolated as directed by the manufacturer, test the injector’s electrical condition and compare the result with the manufacturer's specification.
- If the injector and wiring pass, test the cylinder 8 injector B driver circuit at the control module using the manufacturer's procedure.
Common fixes
- Clean and secure a corroded or loose cylinder 8 injector B connector.
- Repair a short to ground, open, or damaged wire in the cylinder 8 injector B circuit.
- Replace cylinder 8 injector B if its electrical test is outside the manufacturer's specification.
- Repair or replace the control module only if its cylinder 8 injector B driver fails the specified tests.
Can I keep driving?
If the engine runs smoothly and the warning light is steady, restrict driving to necessary short trips and avoid heavy acceleration. Stop if the light flashes, the engine misfires severely, or power drops sharply; an ongoing 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.