Code Definition

B0408 — Temperature control Circuit malfunction - Circuit 1

System: Body  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About B0408

B0408 is a generic (obd-ii standard) body diagnostic trouble code. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B0408 is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

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.

Because B0408 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The HVAC control module operates the temperature blend door actuator on circuit 1 (driver side on dual-zone systems, or the only blend door on single-zone systems) to position the blend door inside the heater box, controlling how much air is routed across the heater core versus bypassing it. The actuator is a small reversible DC motor with an internal feedback potentiometer or hall sensor reporting actual door position. DTC B0408 is set when the module detects an electrical malfunction on the actuator drive or feedback circuit — open, shorted, high-resistance, or a stalled motor that fails t...

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