What Does B1849 Mean?
B1849 indicates the Body Control Module (BCM) or Climate Control Module has detected an abnormal voltage or resistance reading in the temperature differential sensor circuit within the HVAC system. This sensor monitors temperature variance between different zones or between ambient and cabin temperatures to regulate climate control output. The fault suggests the module cannot properly measure or calculate temperature differences needed for automatic climate control operation.
Common Causes
40%
Faulty temperature differential sensor or dual-zone temperature sensor
30%
Damaged wiring harness, corroded connectors, or loose connections in temperature sensor circuit
20%
Failed climate control module or BCM internal circuit fault
10%
Short circuit to power or ground in temperature sensor wiring
Diagnostic Steps
1
Step 1: Perform visual inspection of all temperature sensor connectors and wiring harness in HVAC system for corrosion, damage, loose connections, or pinched wires. Check for water intrusion in sensor locations.
2
Step 2: Using a digital multimeter, measure resistance across temperature differential sensor terminals with connector disconnected. Compare readings to manufacturer specifications (typically 1-5k ohms at room temperature for thermistors). Check for open circuit (infinite resistance) or short circuit (near-zero resistance).
3
Step 3: With ignition on and sensor disconnected, measure reference voltage from climate control module at sensor connector. Verify 5V reference and good ground (typically less than 0.1V to chassis ground). Wiggle wiring harness while monitoring voltage for intermittent faults.
4
Step 4: If sensor and wiring test normal, monitor live temperature sensor data using scan tool climate control module data stream. Compare driver and passenger side temperature readings or ambient versus evaporator readings for unrealistic values or frozen data.
5
Step 5: Clear codes and operate climate control through all modes and temperature settings while monitoring for code return. If code returns immediately with known-good sensor, suspect climate control module internal fault requiring module replacement and programming.
Estimated Repair Cost
$120 - $650
Parts + labor, varies by vehicle and location
B1849 indicates the Body Control Module (BCM) or Climate Control Module has detected an abnormal voltage or resistance reading in the temperature differential sensor circuit within the HVAC system. This sensor monitors temperature variance between different zones or between ambient and cabin tempera...
The most common cause of B1849 (Climate Control Temperature Differential Circuit Failure) is: Faulty temperature differential sensor or dual-zone temperature sensor
Typical repair costs for B1849 range from $120 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is completely safe to drive with this code present. The only impact is reduced automatic climate control functionality - the system may not properly regulate dual-zone temperatures or automatic temperature adjustments, requiring manual temperature control adjustments. Repair can be scheduled at convenience.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1849 to identify the root cause.
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Quick Info
Category
Body
System
Climate Control System (HVAC)
Difficulty
Type
Manufacturer
Recommended Tools
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