What Does B2456 Mean?
This code indicates the body control module (BCM) or engine control module (ECM) has detected a short circuit to ground in the auxiliary heater coolant temperature sensor circuit. The auxiliary heater system, commonly found in diesel vehicles or cold-climate gasoline vehicles, uses this sensor to monitor coolant temperature for proper operation of the supplemental heating system. The control module detected voltage levels below the expected range, indicating the signal wire is shorted to chassis ground or battery negative.
Common Causes
45%
Damaged, chafed, or pinched wiring harness causing short to ground between sensor and control module
30%
Failed auxiliary heater coolant temperature sensor with internal short to ground
15%
Corroded or moisture-damaged sensor connector causing short circuit
10%
Control module internal fault or grounded circuit board trace
Diagnostic Steps
1
Step 1: Perform visual inspection of auxiliary heater coolant sensor, connector, and wiring harness from sensor to control module. Look for chafed insulation, pinched wires, corrosion, moisture intrusion, or damage from heat or moving components
2
Step 2: Disconnect auxiliary heater coolant sensor connector and measure resistance from sensor signal pin to ground using digital multimeter. Reading should be infinite (open circuit). If continuity exists, sensor has internal short and requires replacement
3
Step 3: With sensor disconnected, measure resistance from sensor signal wire (harness side) to chassis ground. Reading should be infinite. If continuity exists, trace wiring harness to locate short to ground point and repair damaged section
4
Step 4: Inspect sensor connector terminals for corrosion, bent pins, or moisture. Clean with electrical contact cleaner and dielectric grease if corroded. Check connector lock mechanism for proper engagement
5
Step 5: If all wiring and sensor test normal, perform voltage supply test at sensor connector with ignition on. Should see reference voltage (typically 5V). If voltage absent or incorrect, suspect control module fault or power/ground circuit issue
6
Step 6: Clear codes, reconnect all components, and perform functional test of auxiliary heater system. Monitor live data for coolant sensor reading and verify code does not return during operation
Estimated Repair Cost
$120 - $450
Parts + labor, varies by vehicle and location
This code indicates the body control module (BCM) or engine control module (ECM) has detected a short circuit to ground in the auxiliary heater coolant temperature sensor circuit. The auxiliary heater system, commonly found in diesel vehicles or cold-climate gasoline vehicles, uses this sensor to mo...
The most common cause of B2456 (Aux Heater Coolant Sensor Circuit Short to Ground) is: Damaged, chafed, or pinched wiring harness causing short to ground between sensor and control module
Typical repair costs for B2456 range from $120 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this affects only the supplemental heating system and does not impact primary engine operation or safety systems. Repair at convenience, though heating performance may be reduced in cold weather conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2456 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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