What it means
The control module detected a low electrical signal in the cylinder 5 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
Injector B is the second injector circuit identified for cylinder 5 by the control system; the code indicates an electrical signal fault rather than proving a fuel-delivery problem. The control module sets P21E4 when the cylinder 5 injector B signal is lower than expected, often from a short to ground, poor connection, or injector electrical failure.
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
- Review freeze-frame data and check for cylinder 5 misfire and related injector codes to see what was happening when the signal dropped.
- Inspect the cylinder 5 injector B connector and harness for loose or corroded pins, chafing, broken insulation, or pinched wires.
- Use the vehicle wiring information to identify the circuit and check for an unintended short to ground.
- With the circuit isolated as the manufacturer directs, check connector condition and wiring continuity for an open or grounded conductor.
- Test injector B for cylinder 5 against the manufacturer’s electrical specification.
Common fixes
- Reconnect and secure the cylinder 5 injector B connector, cleaning corrosion if necessary.
- Repair damaged or shorted-to-ground wiring in the cylinder 5 injector B circuit.
- Replace a loose or corroded terminal that cannot maintain a reliable connection.
- Replace injector B for cylinder 5 if it fails the manufacturer’s electrical test.
Can I keep driving?
If the engine runs roughly or lacks power, avoid heavy loads because continued misfiring can increase emissions and damage the catalytic converter. Stop if the engine runs severely unevenly or the warning light flashes.
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.