Powertrain, generic · Transmission

P0858 Traction Control Input Signal Low

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. P0858 means a wired signal stays below its lower limit: short to ground, an open line without pull-up, or a sending module without power. No maker documents the code; the request is discarded and traction control switched off.

Likely causes

Signal wire from brake module to engine module shorted to ground
Open circuit or connector fault
Brake module without power or ground, or faulty
Input of the engine 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

P0856P0857P0859U0121

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