Cause
Faulty ABS hydraulic modulator
The valve block that ABS uses to control brake pressure at each wheel independently — a set of inlet and outlet solenoid valves, a pump, and an accumulator, all in one casting.
Valves inside it are not separately serviceable on most vehicles, so a genuine valve failure means the assembly. That makes it expensive, and it makes the cheap checks worth doing properly first: the connector and harness live in the engine bay taking heat, vibration and salt, and they fail far more often than the valves.
Its commonest real failure is contamination rather than electrical. Brake fluid absorbs water over years; the corrosion and debris that follow are exactly the size to jam passages and valve seats that are measured in fractions of a millimetre. Fluid that has never been changed is a finding, not a footnote.
A valve stuck closed is more serious than one stuck open, because it can leave a wheel's brake applied — which drags, overheats and pulls the car to one side.
Typically specialist work. Needs equipment or training most home workshops do not have.
Some of these codes mean you should stop driving
4 of the 17 codes this can cause indicate a fault where continuing to drive risks damage or is unsafe. Which one you have matters more than the cause does — read the code's own page before deciding.
Codes this can cause (17)
Codes where this is a likely explanation first, rather than merely a possible one.
- C0001 TCS Control Channel A Valve 1 Likely for this code Moderate
- C0002 TCS Control Channel A Valve 2 Likely for this code Moderate
- C0003 TCS Control Channel B Valve 1 Likely for this code Moderate
- C0004 TCS Control Channel B Valve 2 Likely for this code Moderate
- C0010 Left Front Inlet Control Likely for this code Moderate
- C0011 Left Front Outlet Control Likely for this code Moderate
- C0012 Left Front Hydraulic Release Too Long Likely for this code Stop driving High
- C0014 Right Front Inlet Control Likely for this code Moderate
- C0015 Right Front Outlet Control Likely for this code Moderate
- C0016 Right Front Hydraulic Release Too Long Likely for this code Stop driving High
- C0018 Left Rear Inlet Control Likely for this code Moderate
- C0019 Left Rear Outlet Control Likely for this code Moderate
- C001A Left Rear Hydraulic Release Too Long Likely for this code Stop driving High
- C001C Right Rear Inlet Control Likely for this code Moderate
- C001D Right Rear Outlet Control Likely for this code Moderate
- C001E Right Rear Hydraulic Release Too Long Likely for this code Stop driving High
- C0020 ABS Pump Motor Control Likely for this code Moderate
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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