What does it mean?
C1278 is a Chassis (ABS, traction control, steering) fault code. It indicates: Traction Control Inlet Valve Coil Circuit Short .
Symptoms
- ABS, traction and stability lamps on with the systems disabled
- Blown ABS system fuse in some cases, taking the whole unit offline
- Traction control does not intervene during wheel spin
- Code sets immediately at key on and cannot be cleared
- Buzzing or clicking from the hydraulic unit at start-up may stop altogether
Likely causes
- Traction control inlet valve coil shorted internally, measuring far below the normal resistance
- Control wire chafed and shorted to ground against the modulator bracket or subframe
- Control wire shorted to battery voltage where the loom has been pinched
- Water in the hydraulic unit connector bridging adjacent terminals
- Corrosion inside the modulator after long-term moisture ingress
- Damaged harness after underbody impact or previous repair work
- Module valve driver damaged by the short and now shorted itself
How to fix it
- Check the ABS fuses before anything else, since a shorted coil often takes them out
- Unplug the hydraulic unit connector and measure the suspect valve coil resistance; a very low reading confirms a short
- Compare that value with the other valve coils in the same unit
- With the connector unplugged, test the control circuit for short to ground and short to battery voltage
- Inspect the connector and the loom around the modulator for water, chafing and crush damage
- Repair the shorted harness section and reseal the connector
- Replace the hydraulic modulator when the coil is internally shorted, and check the module driver afterwards