What does it mean?
B2457 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Pedal Motor Sensor Vcc Error .
Symptoms
- The auxiliary heater does not start, or starts and then shuts down during the warm up phase
- No heat contribution from the auxiliary heater on cold starts
- The heater coolant temperature value reads at the extreme cold end of the scale in all conditions
- A heater lockout that has to be reset with a scan tool
- Remote or timer preheating fails to deliver a warm cabin
Likely causes
- Open element inside the auxiliary heater coolant temperature sensor
- Sensor connector unplugged or a terminal pushed out of its housing
- Broken signal or ground wire between the sensor and the heater control unit
- Corroded connector on an underbody or wheel arch mounted heater
- Heat damage to the wiring where it passes close to the heater exhaust
- Open sensor ground shared with the other heater sensors
- Faulty input stage inside the auxiliary heater control unit
How to fix it
- Read the heater coolant temperature value with the vehicle at ambient temperature and compare it with the outside air temperature
- A reading pinned at the lowest value that never changes during warm up points to an open circuit
- Bridge the sensor connector with a suitable test resistance and see whether the reported value changes, which proves the wiring
- Measure the sensor resistance directly; an infinite value confirms the sensor is open
- Check continuity of the signal and ground wires all the way back to the heater control unit
- Inspect the loom for heat damage near the heater exhaust and repair it with high temperature protection
- Replace the sensor when it measures open, reset the heater lockout and confirm a complete burn cycle