What Does B2457 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the auxiliary heater coolant temperature sensor circuit. The auxiliary heater is a supplemental heating system that warms engine coolant to provide cabin heat faster in cold conditions. An open circuit means the BCM cannot receive temperature data from this sensor due to a broken wire, disconnected connector, or failed sensor.
Common Causes
45%
Damaged or corroded wiring harness and connector at the auxiliary heater coolant sensor
30%
Failed auxiliary heater coolant temperature sensor with internal open circuit
15%
Broken or chafed wires between BCM and auxiliary heater sensor
10%
BCM internal fault or poor ground connection at BCM
Diagnostic Steps
1
Step 1: Perform visual inspection of the auxiliary heater coolant sensor connector for corrosion, pushed-out pins, water intrusion, or physical damage. Check sensor mounting area for coolant leaks that may have damaged wiring.
2
Step 2: Disconnect the auxiliary heater coolant sensor connector and measure resistance across the sensor terminals using a digital multimeter. Compare readings to manufacturer specifications (typically 2000-3000 ohms at room temperature). An infinite reading confirms sensor failure.
3
Step 3: With sensor disconnected, check continuity of both signal and ground wires from the sensor connector back to the BCM connector using a multimeter. Resistance should be less than 1 ohm for each wire. Wiggle harness during testing to identify intermittent opens.
4
Step 4: Check for proper ground at the sensor ground circuit by measuring voltage drop between sensor ground terminal and battery negative with auxiliary heater operating. Voltage drop should be less than 0.1 volts.
5
Step 5: If all wiring tests pass, substitute a known-good auxiliary heater coolant sensor or measure sensor resistance while heating in water bath to verify sensor responds correctly to temperature changes.
6
Step 6: Clear codes, cycle auxiliary heater operation through multiple heating cycles, and verify repair by confirming no code returns and BCM displays valid temperature readings on scan tool live data.
Estimated Repair Cost
$120 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the auxiliary heater coolant temperature sensor circuit. The auxiliary heater is a supplemental heating system that warms engine coolant to provide cabin heat faster in cold conditions. An open circuit means the BCM ca...
The most common cause of B2457 (Aux Heater Coolant Sensor Circuit Open) is: Damaged or corroded wiring harness and connector at the auxiliary heater coolant sensor
Typical repair costs for B2457 range from $120 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This code does not affect vehicle safety or drivability and the vehicle can be operated normally. The auxiliary heater may not function, resulting in slower cabin heating in cold weather conditions, but primary engine cooling and heating systems remain unaffected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2457 to identify the root cause.
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Quick Info
Category
Body
System
Auxiliary Heating System
Difficulty
Type
Generic (SAE)
Recommended Tools
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