Code Definition

B1138 — Cabin Heater 3 Control Circuit Low

System: Body  |  Type: Manufacturer-Specific  |  Make: Jeep

About B1138

B1138 is a manufacturer-specific body diagnostic trouble code recorded for Jeep vehicles. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1138 is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1138 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The HVAC Control Module (or Automatic Temperature Control module) monitors the voltage on the cabin heater 3 (blower speed 3) resistor control circuit when that speed is selected. The circuit typically runs from the HVAC module through the blower resistor pack and back to the blower motor, with the resistor pack dropping voltage to produce the lower blower speeds. DTC B1138 is logged when the module detects a persistently low voltage, typically below approximately 1V, on that circuit for longer than the defined threshold while commanding speed 3, indicating a short to ground condition or an in...

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