C0004 indicates an electrical fault in the traction‑control system’s valve 2, typically a solenoid inside the ABS/TCS hydraulic unit. The code is set when the brake/traction‑control module detects an open circuit, short, or abnormal operation in that valve’s control channel.
The coil inside valve 2 can open, short, or become contaminated, causing the control module to detect an electrical fault.
Chafed wires, broken pins, or corrosion at the valve harness can prevent proper voltage or ground, triggering the code.
A failed fuse or relay in the valve’s power circuit creates an open circuit that sets C0004.
Low brake‑fluid level or insufficient pressure can affect valve operation and may indirectly lead to fault detection, though the primary fault is usually electrical.
The module that commands the valve may fail to send correct signals, but this is a less common cause and should be investigated only after the valve and wiring have been verified.
Yes – normal hydraulic braking remains functional. The fault only disables or reduces the traction‑control and stability‑assist functions.
You can typically drive, but you should avoid heavy acceleration on slippery surfaces and have the issue diagnosed promptly to restore full safety systems.
In most cases the fault lies in the valve, wiring, or a blown fuse. PCM replacement is rarely required and is usually not the correct fix for this code.
Low fluid can affect TCS operation, but C0004 specifically indicates an electrical fault in valve 2. Check the valve and wiring first; address fluid level as a separate concern.