Code Definition

C1939 — Brake Pressure Switch Input Circuit Failure

System: Chassis  |  Type: Manufacturer-Specific  |  Make: Generic

About C1939

C1939 is a manufacturer-specific chassis diagnostic trouble code. It belongs to the C-prefix family of codes, which covers chassis, braking, steering, suspension, or stability-control faults.

When C1939 is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

Scanning & clearing: Chassis (C) codes are stored in the ABS, traction control, or stability-control modules. An enhanced or OEM-level scan tool is usually required to read and clear them.

C1939 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 brake pressure switch signals the stability or ABS control module when hydraulic pressure is present in the brake system, confirming that the driver is braking. The module uses this input, often alongside the brake light switch, to support functions such as ABS, traction control, stability control, hill hold, and brake assist. DTC C1939 sets when the module detects an electrical fault in the brake pressure switch input circuit, such as an open, a short to ground, a short to voltage, or a switch state that does not agree with the expected condition. When this code is set the related braking...

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