Powertrain, generic · Transmission

P0856 Traction Control Input Signal

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. GM checks the CAN torque request from the brake module: a wrong protection value or rolling count in 6 of 10 messages, or three changes of request type within 200 ms, set it, type C without MIL. On the Saab 9-4X the brake module then switches traction and stability control off for the key cycle and stores C0242.

Likely causes

Fault in the engine module that prevents torque reduction, often with other engine codes
Software of engine or brake module, module faulty
CAN fault, connector or ground at the brake or engine module
Low supply voltage

Symptoms

  • Traction or stability control lamp on, system switched off
  • No torque reduction when wheels spin
  • Usually no check engine lamp
  • C0242 or similar in the brake module

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–1,200
Time0.5–3 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

P0857P0858P0859U0121U0415U0416

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com.