For 1990-2009 cars only
- Block the wheels.
- Pull out the system park knob (1).
- Pull out the trailer air supply (3).
- Test the vehicle dual air pressure gauge for accuracy with the test gauge.
- Install the test gauge and hose coupling on the trailer supply coupling (tractor emergency hose coupling) at the rear of the cab.
- Start the engine.
- Charge the system air pressure to the governor cut-out point.
- Verify the test gauge reads zero.
- Push in the trailer air supply knob (3).
- Verify that the test gauge reads zero. If the gauge shows air pressure, replace the valve (2).
- Push in the system park knob.
- Verify that the test gauge reads about the same as the dual air pressure gauge.
- If not, check for leaks or blockages in the air lines. If the air lines are not blocked or leaking, replace the valve (2).
- Turn off the engine with the system at the governor cut-out point.
- Disconnect the test gauge and the hose coupling from the trailer supply line coupling.
- Verify that the valve knob (3) pops out.
- Check that the supply pressure remaining is 276-448 kPa (40-65 psi) as indicated on the dual air pressure gauge.
- If the remaining pressure is not within these limits, replace the valve (2) .
- Set the parking brake.
- Remove the wheel blocks.
