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B1949 OBD-II Trouble Code: Climate Control Water Temperature Sensor Circuit Failure

diagnostic check engine light

B1949 code definition

The B1949 code is a manufacturer-specific body code related to the climate control system. In this case, the engine control module (ECM) has detected a failure in the circuit for the climate control water temperature sensor.

What the B1949 code means

A code B1949 will be stored when the ECM detects a coolant temperature signal circuit fault between the instrument pack and air conditioning/climate control unit (A/CCM). The A/CCM receives an engine coolant temperature voltage signal from the instrument pack.

The A/CCM monitors the engine coolant temperature circuit for open circuit, high resistance and short circuit conditions. If a fault is present, a DTC will be flagged. If a circuit fault occurs between the coolant temperature sensor and the instrument pack, the instrument pack output will default to a voltage equal to 20 °C (68 °F). If a circuit fault occurs between the instrument pack and the A/CCM, the A/CCM will substitute a default value of 76 °C (169 °F).

What causes the B1949 code?

Several problems may cause a B1949 code including:

  • Damaged or defective wiring and related electrical components
  • Signal circuit between instrument pack and A/CCM short circuit to ground
  • Harness/wiring problems between heater valve and climate control module
  • Fault or failure at one (or more) of the air mixing/blending flaps
  • Fault in the pressurized A/C system, including condenser fan, compressor, refrigerant pressures/leaks
  • Damaged or defective heater fan
  • Damaged or defective climate control module

What are the symptoms of the B1949 code?

Symptoms of a B1949 code may include:

  • Check engine or warning light may illuminate
  • The air condition/climate control system may not function correctly (for example, only blowing warm air when air conditioner is cranked on)

How does a mechanic diagnose the B1949 code?

A mechanic may use several methods to diagnose a B1949 trouble code, including:

  • Utilize an OBD-II scanner to check for a stored B1949 trouble code
  • Visually inspect wiring and related electrical components for damage or defects
  • Visually inspect for any leaks in the A/CCM system
  • Check operation of pressured air conditioning system
  • Check the fuse for the heater valve to see if blown or damaged
  • Check the connection to the heater valve for damage or loose connectors or corrosion on the valve itself
  • Check the evaporator discharge temperature sensor(s) for damage or defect
  • Test the voltage, current, and resistance on the heater valve

How serious is the B1949 code?

Because a vehicle’s safe driving operation will not be impacted due to faults that store a B1949 code, this code is not considered a serious code. When this code appears, it is recommended to take your vehicle to your local service center or mechanic for repair and diagnosis as soon as possible.

What repairs can fix the B1949 code?

Several repairs can fix a B1949 trouble code and include:

Additional information related to a B1949 code

With any repairs related to the electrical components of your vehicle, it is recommended to review your vehicle’s service manual, and if possible utilize the assistance of a professional to avoid additional costly repairs.

Need help with a B1949 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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