What it means
The negative contactor B of the battery charging system reports a stuck open condition. HV charging path cannot be commanded reliably.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Negative contactor B is a high-voltage switch in the battery charging path. The hybrid control module checks whether the contactor closes when commanded; this code sets when feedback indicates that B remains open.
Common causes
Most likely first.
- Contactor contacts oxidised - high resistance
- Contactor coil burned out
- Carbon or debris buildup preventing free movement
Symptoms
- Hybrid-system warning light or message
- Vehicle may not enter READY mode
- Charging may be unavailable
How to diagnose it
- Record freeze-frame data and check hybrid-system live data for the command and reported state of negative contactor B, since this confirms when the mismatch occurs.
- Check the vehicle's service information for the specified safe diagnostic procedure, then inspect accessible low-voltage wiring and contactor B connectors for looseness, corrosion, or damage.
- Use the scan tool's supported output test to command contactor B closed and compare the command with its reported state.
- With the high-voltage system made safe according to the manufacturer's procedure, test the contactor coil and circuit continuity against the manufacturer's specification.
- Check the contactor contacts and mechanism for oxidation, high resistance, or obstruction, then verify READY and charging operation after repair.
Common fixes
- Clean or repair corroded or loose low-voltage connector terminals at contactor B.
- Repair damaged wiring or a connector that interrupts the coil circuit.
- Replace negative contactor B if its coil is open or its contacts have excessive resistance.
- Remove the cause of mechanical binding, or replace the contactor if it remains stuck.
Can I keep driving?
The vehicle may not enter READY and charging may be unavailable, so avoid trips that depend on reliable hybrid operation. Arrange prompt diagnosis and do not handle high-voltage components.
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.