Air system leaks
Block the vehicle wheels and check the air system for leaks with service brakes applied and released. Check for leaks from the air compressor gaskets and the air system hoses, fittings, tanks, and valves. For applications fitted with selective catalytic reduction exhaust systems, check the air supply line to the dosing control unit. Refer to Procedure 012-019 in Section 12 and the OEM service manual.
Air governor is malfunctioning or not set correctly
Check the air governor for correct operation. Refer to Procedure 012-016 in Section 12 and the OEM service manual.
Air compressor unloader and valve assembly is malfunctioning
Check the unloader valve operation and unloader body seal. Refer to Procedure 012-013 in Section 12. If required, clean the air compressor cylinder head. Refer to Procedure 012-003 on Section 12.
Air compressor intake or exhaust valve system leaks air
Leak Test the air compressor head assembly intake and exhaust valve. Refer to Procedure 012-014 in Section 12. The intake and exhaust valve on the air compressor head are not serviceable, replace the air compressor cylinder head. Refer to Procedure 012-007 in Section 12.