C0300 code meaning
Inlet Valve Front Left Performance
What C0300 means
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.
C0300 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C0300
- ABS and stability control warning lamps on
- Car pulls during hard braking
Common causes of C0300
- PossibleInlet valve sticking from contaminated or aged brake fluid
- PossibleValve coil or driver in the brake module faulty
- Less likelyOn GM 4WD trucks, rear speed sensor fault in the transfer case system (GM meaning of the number)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Lf ABS inlet valveABS hydraulic blockABS control module
What each part of C0300 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 C0300 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 C0300
What does C0300 mean?
C0300 means "Inlet Valve Front Left Performance". C0300 appears in none of the published J2012 lists, and no maker documents it as an ABS valve code. It is a generic code, so it means the same on every make.
Is it safe to drive with C0300?
Drive gently and only to a workshop. With C0300 the car can go into limp mode (reduced power) to protect itself.
Will C0300 fail an emissions test?
C0300 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 C0300 to fix?
Difficulty: hard. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will C0300 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.