C0400 code meaning
Traction Control Solenoid Valve Circuit
What C0400 means
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.
C0400 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C0400
- ABS, traction control and stability warning lamps on
- Wheels spin freely when pulling away on slippery ground
Common causes of C0400
- PossibleOpen or shorted coil of a traction control valve
- PossibleValve driver inside the brake control module failed
- Less likelyPoor supply or ground of the brake control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Tcs isolation valveABS hydraulic blockABS control module
What each part of C0400 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 00 | The exact fault in that area. |
What to do next
- Note C0400 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C0400
What does C0400 mean?
C0400 means "Traction Control Solenoid Valve Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with C0400?
Drive gently and only to a workshop. With C0400 the car can go into limp mode (reduced power) to protect itself.
Will C0400 fail an emissions test?
C0400 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C0400 to fix?
Difficulty: workshop only. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will C0400 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.