What it means
The control module detected a high electrical signal in the cylinder 2 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 2 by the control system; P21DF concerns its electrical signal, not proof of incorrect injector flow. The control module sets this code when the signal is higher than expected, which can result from a short to voltage, connector damage, or an injector electrical 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 for cylinder 2 misfire or related injector codes to establish when the high-signal fault appears.
- Inspect the cylinder 2 injector B connector and harness for corrosion, loose terminals, damaged insulation, or contact with a powered wire.
- Use the wiring information to identify the circuit and check for a short to voltage, following the manufacturer’s safe circuit-isolation procedure.
- With the injector disconnected as directed, check the harness for unintended voltage and verify circuit continuity and terminal condition.
- Test injector B for cylinder 2 against the manufacturer’s electrical specification to distinguish an injector fault from a harness fault.
Common fixes
- Secure the cylinder 2 injector B connector and clean or replace corroded terminals.
- Repair wiring with damaged insulation or a short to voltage in the circuit.
- Replace a damaged connector that cannot hold or insulate its terminals properly.
- Replace injector B for cylinder 2 if it fails the manufacturer’s electrical test.
Can I keep driving?
A rough-running or misfiring engine can produce excess emissions and may damage the catalytic converter, so avoid heavy loads and have the fault addressed promptly. Stop driving 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.