P0859: Traction Control Input Signal High
What to do
The car drives normally but traction and stability control are probably switched off — you will only discover that in conditions where you need them. Worth repairing before winter rather than after the first slippery morning.
What this code means
The traction control request circuit reads above its valid range — an open circuit or a short to supply. Most commonly the engine simply never receives a torque reduction request, so traction control loses one of its two tools and disables itself rather than intervene with brakes alone.
A vehicle in that state drives entirely normally in ordinary conditions and is missing a safety system in poor ones, which is the sort of fault that is easy to postpone through a dry summer and remembered sharply in the first frost.
Likely causes
Start here
- Open circuit in module wiring · moderate
- Corroded or loose connector · easy
Less common
- Faulty stability control module · specialist
- Wiring shorted to voltage · moderate
Symptoms
Components involved
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.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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