Chassis, generic

C0300 Inlet Valve Front Left Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0300 appears in none of the published J2012 lists, and no maker documents it as an ABS valve code. GM uses the number: it is among the chassis keywords of PIP5094, and AA1Car's GM table calls it Rear Speed Sensor Malfunction, listed in the same block as the transfer case motor codes C0306 to C0315. The title describes the front left inlet valve of the ABS valve block. That valve is open at rest and closes during a regulation cycle to hold pressure at the wheel; TRW, in the 2011 Saab 9-5, calls it the isolation valve. Saab's older 9-5 pulses every valve for 20 ms at each ignition-on and, on a fault, switches off ABS, traction and stability control with their warning lamps. A sluggish front left inlet valve leaves that wheel under- or overbraked during ABS.

Likely causes

Inlet valve sticking from contaminated or aged brake fluid
Valve coil or driver in the brake module faulty
On GM 4WD trucks, rear speed sensor fault in the transfer case system (GM meaning of the number)

Symptoms

  • ABS and stability control warning lamps on
  • Car pulls during hard braking

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,500
Time1–3 h

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

Parts involved

lf abs inlet valveabs hydraulic blockabs control module

Related codes

C0302C0303C0305

References: static.nhtsa.gov, aa1car.com, saabwisonline.com, saabwisonline.com.