Chassis, generic

C0400 Traction Control Solenoid Valve Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0400 is publicly undocumented: none of the published J2012 lists contains it, neither does GM's PIP5094, and a search of NHTSA's bulletin index finds nothing. Only the part from the title is described here. For traction control the brake unit must build pressure without the driver pressing the pedal. In the TC/ABS unit of the 2004 Saab 9-5 one pressure build valve and one pressure release valve per front wheel are used only in TCS mode, while the return pump supplies fluid; Bosch likewise places all control valves and the pump in one hydraulic unit. Each time the ignition comes on, the Saab module tests each valve with a 20 ms pulse; if one fails it switches off ESP, TCS and ABS and lights ABS, brake and ESP OFF lamps.

Likely causes

Open or shorted coil of a traction control valve
Valve driver inside the brake control module failed
Poor supply or ground of the brake control module

Symptoms

  • ABS, traction control and stability warning lamps on
  • Wheels spin freely when pulling away on slippery ground

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–1,800
Time1–4 h

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

Parts involved

tcs isolation valveabs hydraulic blockabs control module

Related codes

C0401C0405C0300

References: saabwisonline.com, saabwisonline.com, bosch-mobility.com.