What does it mean?
B2456 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Seat Motor Sensor Vcc Error .
Symptoms
- The auxiliary heater refuses to start or stops soon after ignition
- The heater cuts out because the control unit believes the coolant is already hot
- The cabin does not warm up in cold weather even with the heater requested
- The heater runs at reduced output or in a fault mode
- An auxiliary heating error is shown on the timer or the remote unit
Likely causes
- Shorted thermistor inside the auxiliary heater coolant temperature sensor
- Coolant leaking past the sensor seal and sitting in the connector
- Signal wire chafed against the heater body or a coolant pipe clamp
- Corrosion bridging the signal and ground pins after water ingress
- Loom crushed between the heater unit and its mounting bracket
- Damage caused by previous coolant hose or heater work in the same area
- Shorted input inside the auxiliary heater control unit
How to fix it
- Read the auxiliary heater coolant temperature value and compare it with engine coolant temperature on a completely cold vehicle
- A value stuck at the hot end of the scale usually means the signal is grounded
- Unplug the sensor and see whether the reported value jumps to the opposite extreme, which shows the harness is not shorted
- Measure the sensor resistance against the temperature to resistance table
- Test the signal wire to ground with both ends disconnected to find a harness short
- Dry and clean or replace a connector contaminated by coolant, and cure the leak that caused it
- Replace the sensor when it is internally shorted, then reset the heater lockout and run a full cycle