P0859
Traction Control Input Signal High
Traction control input
Generic OBD-II
Medium
What it means
P0859 sets when the traction control input signal is stuck high (excessive voltage) instead of reading a valid value. It points to the switch, wiring, or module on the traction control input circuit. The engine and transmission are unaffected — the car starts and drives normally — but traction and stability control may be turned off, so grip management on slippery roads can be compromised.
Medium
Can I keep driving? The car starts and drives normally, but traction/stability control may be disabled — take extra care on wet, snowy, or loose surfaces until it's fixed.
Common symptoms
What you'll notice
- Check-engine light and often a traction/stability control warning light
- Traction control disabled or not working
- Reduced grip management on slippery roads
- Erratic or inconsistent traction control operation
Common causes
Most likely first
- Faulty traction control switchLikely
- Short to voltage or wiring fault in the traction control input circuitCommon
- Loose or corroded connectors in the traction control systemCommon
- Faulty traction control or ABS moduleLess often
- Intermittent fault in the input circuitLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and note whether the input reads high (near battery voltage) constantly.
- Inspect the traction control switch and input wiring for a short to power or a chafed harness.
- Clean and reseat connectors in the traction control circuit.
- Test the switch operation, then the module input, replacing the switch if it fails.
- If the circuit checks good, have the traction control/ABS module tested. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0859?+
Yes for normal driving, but with traction control disabled you have less help on slippery surfaces. Drive cautiously in poor conditions until it's repaired.
Can I just clear P0859?+
It will come back while the input circuit reads high. The switch and its wiring are the usual culprits and are worth checking before the module.
Related codes
Read & clear P0859 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX