Air intake system restriction to air compressor is excessive
Replace the air compressor air cleaner (if installed). Check the air intake piping. Check the engine air intake restriction if the air compressor air inlet is plumbed to the vehicle or equipment intake system. Refer to Procedure 010-031 in Section 10 to measure the intake restriction.
Air system leaks
Block the vehicle wheels and check the air system for leaks with spring brakes applied and released. Check for leaks from the air compressor gaskets and the air system hoses, fittings, tanks, and valves. Check for air system leaks in the catalyst dosing control unit. Refer to the OEM service manual. 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.
Air governor is malfunctioning or not set correctly
Check the air governor for correct operation. Some OEM installations may not utilize an air governor, therefore frequent cycling may be expected and normal. Refer to Procedure 012-016 in Section 12 and the OEM service manual.
Carbon buildup is excessive in the air discharge line or downstream air valves
Check for carbon buildup. Clean or replace the air compressor discharge line, as necessary. Check the turbocharger for oil leaks. Check the air compressor intake tube for oil. Refer to Procedure 012-003 in Section 12.
Unloader valve is malfunctioning
Check the unloader valve and unloader body seal. Refer to Procedure 012-013 in Section 12 and the OEM service manual. If required, clean the air compressor cylinder head. Refer to Procedure 012-003 in 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 valves on the air compressor head are not serviceable, replace the air compressor cylinder head. Refer to Procedure 012-007 in 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 valves on the air compressor head are not serviceable, replace the air compressor cylinder head. Refer to Procedure 012-007 in Section 12.
Air system component is malfunctioning
Check the operation of check valves, alcohol evaporators, air dryers, and other OEM-installed air system components. Refer to the OEM service manual.