C0400
Traction Control Solenoid Valve Circuit
The dedicated traction control isolation valve in the hydraulic block reports an electrical fault.
- Check engine light: Not always
- Emissions related: No
- Repair difficulty: hard
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Common causes
Ordered by how often each turns out to be the cause.
- Solenoid coil openCommon
- Short to groundPossible
Parts involved
- Tcs Isolation Valve
- ABS Hydraulic Block
- ABS Control Module
C0400 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.