Powertrain, generic · Transmission

P0859 Traction Control Input Signal High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The traction control input carries the request of the ABS/stability module to the engine module to cut torque when wheels spin. Older cars used a wire with a voltage or duty-cycle signal, hence the low and high variants; today it is a CAN message, where pure loss of communication sets U0121 or U0415 instead. California's OBD rule counts traction control as a safety-only system that may be exempted, so these codes normally carry no MIL. P0859 means a wired signal stays above its upper limit: short to battery or 5 V, or an open line with a pull-up in the receiver. No maker documents the code; the request is discarded and traction control switched off.

Likely causes

Signal wire shorted to voltage
Open circuit with pull-up in the engine module
Ground fault of the brake module
Module faulty

Symptoms

  • Traction or stability control lamp on, system switched off
  • No torque reduction when wheels spin

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–800
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

abs control moduleengine control moduleserial data linesensor wiring

Related codes

P0856P0857P0858U0121

References: law.cornell.edu, gsi.ext.gm.com, saabwisonline.com.