Code Definition

C1178 — Speed Wheel Sensor LR Coherency Fault

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

About C1178

C1178 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 C1178 is stored, the module has detected a sensor-related fault — the reported value from the named sensor is out of spec.

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.

C1178 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 ABS/EBCM continuously compares the four wheel speed signals against each other and against expected vehicle behaviour to validate that each reading is plausible. A coherency fault means the left rear wheel speed signal is present but does not agree with the other wheel speeds or with the calculated vehicle speed, for example reading too high, too low, or dropping out briefly when the other three wheels track normally. DTC C1178 sets when the module decides the left rear signal is not coherent rather than fully open or shorted, which points to intermittent sensor output, a damaged tone ring...

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