What it means
Pressure in the service/park brake chamber dropped below required minimum — risk of insufficient braking force.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
On an air-brake vehicle, the service/park brake chamber pressure sensor monitors pressure in the combined service and spring-applied parking brake chamber. C066F sets when pressure falls below the system's required minimum, which can leave insufficient pressure for proper braking.
Common causes
Most likely first.
- Air leak in the brake system or chamber
- Low air supply pressure
- Faulty pressure sensor or inaccurate reading
- Damaged or leaking hose or connection
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Check the vehicle's air-pressure warnings and live chamber pressure data, if available, before moving it.
- Inspect the chamber, hoses, and fittings for audible or visible air leaks, including around the sensor connection.
- Check the air supply and compare its pressure indications with the manufacturer's operating specification.
- Inspect the pressure sensor and wiring for damage or a connection problem that could falsely report low pressure.
- Have actual chamber pressure and the sensor circuit tested against the manufacturer's procedure to distinguish a real pressure loss from a faulty reading.
Common fixes
- Repair leaking hoses, fittings, or the brake chamber.
- Restore the air supply if it is below the manufacturer's specification.
- Repair a damaged sensor connector or wiring.
- Replace a pressure sensor that fails testing against the manufacturer's specification.
Can I keep driving?
Do not drive with low air pressure or a brake warning active; braking force may be insufficient and the spring parking brake may apply. Stop safely and arrange service before moving the vehicle.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.