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
Often seen with P0859
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