What it means
The control module detected a low electrical signal in the cylinder 4 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 4 by the control system; P21E2 indicates a low electrical signal, not necessarily poor fuel delivery. The control module sets it when the cylinder 4 injector B circuit signal falls below its expected level, commonly due to a short to ground, damaged connection, or injector electrical fault.
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
- Check freeze-frame data and scan for cylinder 4 misfire and related injector faults to see when the low signal occurs.
- Inspect the cylinder 4 injector B connector and harness for corrosion, loose pins, abrasion, breaks, or pinched wires.
- Identify the circuit from the vehicle wiring information and check for a short to ground.
- Isolate the circuit as specified by the manufacturer, then check wiring continuity and connector terminal condition.
- Test injector B for cylinder 4 against the manufacturer’s electrical specification to confirm whether the injector itself is faulty.
Common fixes
- Reconnect and secure the cylinder 4 injector B connector; clean corrosion if present.
- Repair damaged wiring or a short to ground in the cylinder 4 injector B circuit.
- Replace a corroded or damaged connector terminal that cannot maintain contact.
- Replace injector B for cylinder 4 if it fails the manufacturer’s electrical test.
Can I keep driving?
Avoid heavy acceleration if the engine is rough or down on power, since continued misfiring can raise emissions and damage the catalytic converter. Stop driving if it 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.