Body
Generic/SAE
OBD-II Fault Code
B2457: Aux Heater Coolant Sensor Circuit Open
Meaning, symptoms, likely causes, diagnostic checks and repair guidance for B2457.
Cooling system
Use this category to narrow your checks before replacing parts.
High
Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.
What B2457 usually means
Aux Heater Coolant Sensor Circuit Open.
Common symptoms
Body/accessory warning lamp or feature not working; Temperature gauge abnormal; Overheating or slow warm-up possible
Likely causes
Low coolant; Faulty thermostat; Coolant temperature sensor/wiring fault; Cooling fan issue; Open circuit; Disconnected connector; Broken wire; Failed component
Diagnostic checks
Check related fuses, connectors, grounds and switch/module power supply; Check coolant level only when engine is cool; Compare scan-tool temperature to actual temperature; Check connector fitment and continuity from module to component
Repair guidance
Repair leaks, replace thermostat/sensor/fan component after confirming fault; Repair open wire/connector or replace the failed component after continuity test
Verification after repair
Operate the affected body/accessory system and rescan