P0859 Traction Control Input Signal High

P0859 indicates a high traction control input signal. The traction request or status path is stuck high, open, or above the expected range.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not assume a high traction input is a transmission fault; verify the ABS and network source first.

Symptoms of P0859

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0859

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Measure the traction input circuit where applicable and compare networked traction status across ABS, powertrain, and transmission modules.
Inspect for short-to-voltage faults, open grounds, connector corrosion, ABS communication problems, and traction switch issues.
Review whether the high input forces torque reduction, stability-control warnings, altered shifts, or limp mode.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.