Air Pressure Excessively Low or High for GMC Truck TopKick C-Series (Conventional) C6/C7/C8 2003

The governor is leaking.

Overhaul or replace the governor.

The air compressor is leaking.

1. Check the fittings, the bolts, and the mating surfaces.
2. Tighten or repair as needed.

The unloader is not functioning.

Overhaul the cylinder head assembly.

The governor is faulty.

Overhaul or replace the governor.