What it means
The control module detected a low electrical signal in the cylinder 3 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 3 by the control system; this code describes an electrical signal issue, not a confirmed fuel-flow problem. The control module sets P21E0 when the cylinder 3 injector B signal is lower than expected, often because of a short to ground, a poor connection, or an 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
- Save freeze-frame data and check for cylinder 3 misfire or related injector codes to see whether the low-signal event matches rough running.
- Inspect the cylinder 3 injector B connector and harness for loose or corroded pins, chafing, broken insulation, or pinched wiring.
- Identify the injector B circuit for cylinder 3 from the vehicle wiring information and check for a short to ground.
- With the circuit isolated as specified by the manufacturer, check connector terminals and wiring continuity for an open or unwanted ground path.
- Measure injector B’s electrical condition for cylinder 3 and compare it with the manufacturer’s specification.
Common fixes
- Reconnect and secure the cylinder 3 injector B connector, cleaning corrosion if needed.
- Repair wiring that is shorted to ground or damaged in the cylinder 3 injector B circuit.
- Replace a loose or corroded connector terminal that cannot maintain contact.
- Replace injector B for cylinder 3 if its electrical test confirms an internal fault.
Can I keep driving?
If the engine is rough or down on power, avoid hard acceleration because continued misfiring can increase 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.