What it means
The control module detected a high electrical signal in the cylinder 9 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 9 injector B is the injector identified for cylinder 9, and its driver circuit carries the electrical command that operates it. The control module monitors the circuit response and sets P21ED when the signal is higher than expected. This points to an electrical issue in the cylinder 9 injector B circuit, such as wiring shorted to voltage, rather than proving a fuel-delivery 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
- Record freeze-frame data and check live misfire counts and fuel trims to determine when the cylinder 9 injector B circuit fault occurs and whether cylinder 9 is affected.
- With the engine off, inspect the cylinder 9 injector B connector and nearby harness for corrosion, loose pins, chafing, heat damage, or contact with a power feed.
- Follow the wiring diagram to check the cylinder 9 injector B circuit for a short to voltage, an open, or a poor connection between the injector and control module.
- Isolate the circuit as directed by the manufacturer and compare the injector’s electrical condition with the manufacturer's specification; note whether the high signal remains with the injector disconnected.
- If the wiring and injector pass, test the cylinder 9 injector B driver at the control module using the manufacturer's procedure.
Common fixes
- Clean and secure a corroded or loose cylinder 9 injector B connector.
- Repair wiring shorted to voltage or damaged in the cylinder 9 injector B circuit.
- Replace cylinder 9 injector B if its electrical test is outside the manufacturer's specification.
- Repair or replace the control module only if its cylinder 9 injector B driver fails the specified tests.
Can I keep driving?
If the engine runs smoothly and the warning light is steady, limit driving and avoid heavy loads until the cause is found. Stop if the light flashes or the engine misfires badly, since continued misfire can overheat and 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.