What it means
The battery charger A input voltage sensor B circuit signal is above the expected threshold. The code does not by itself identify the cause.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Battery charger A uses input voltage sensor B to report an electrical condition at the charger input to the control module. The module sets P0EFA when sensor B's circuit signal rises above its expected range, which can make it misjudge charging conditions.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open sensor
- Connector pins corroded - high contact resistance
Symptoms
- Charge status indicator shows fault
- Charging may not start or interrupts
- Slower-than-expected charge rate
How to diagnose it
- Record freeze-frame data and compare sensor B's live reading with the charger input readings to see when the signal goes high.
- With the vehicle safely powered down according to the manufacturer's procedure, inspect sensor B's connector and wiring for damage, corrosion, loose pins, or contact with a B+ supply.
- Check connector pin contact and continuity, since corrosion or a poor connection can interrupt the sensor circuit.
- Test the signal wire for a short to B+ and check circuit continuity using the manufacturer's procedure.
- If the wiring and connections pass, test sensor B and its reference/ground circuits for an open sensor or failed connection.
Common fixes
- Clean and securely reconnect corroded or loose sensor B connector pins.
- Repair a signal wire shorted to B+ or damaged wiring.
- Restore an open or poor connection in sensor B's circuit.
- Replace input voltage sensor B if testing confirms it is open or faulty.
Can I keep driving?
Charging may not start, may interrupt, or may run more slowly, and charging functions may be limited. Do not rely on normal charging until the fault is diagnosed; follow the vehicle's warnings and charging safety instructions.
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.