Chassis, generic

C0401 Traction Control Switch Circuit

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

There is no public evidence that any maker uses C0401. The code is missing from the publicly available J2012 lists and from GM's PIP5094; the only NHTSA index hit is a BMW program number. The description is limited to the switch itself. On the 2004 Saab 9-5 a spring-loaded dash button beside the steering wheel turns ESP and TCS off together; it grounds a supply from the brake module, works for switching off only below 60 km/h, and after more than ten seconds pressed forces the system on until the next ignition cycle without storing a code. FMVSS 126 allows such an off control but demands that stability control come back in its default mode at every new ignition cycle. A shorted or open button circuit leaves the driver unable to change the mode.

Likely causes

Button stuck pressed or contacts dirty

Open or grounded lead between button and brake module

Liquid spilled into the switch panel

Symptoms

Traction or stability control cannot be switched off or on
TCS OFF or ESP OFF lamp lit permanently

Repair estimate

DifficultyEasyDIY possible

Parts and labour€20–200

Time0.3–1 h

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

Parts involved

tcs switchdashboard wiringabs control module

Related codes

C0400 C0405

References: saabwisonline.com, law.cornell.edu, bosch-mobility.com.