Section ll TROUBLESHOOTING
a. General. The primary use of the compressed air system is to operate the service and park/
emergency vehicle brakes. Other uses of compressed air are for transmission shifting control, air horn
operation, windshield wiper and washer operation, the differential lockout, and on some vehicles,
pusher axle controls, and front wheel drive. Air system component location illustrations for each
truck model are contained in paragraphs 9-5e thru 9-5j. These same illustrations are contained in para-
graphs 2-65 thru 2-70 and the components are further described in paragraph 2-64.
b. Scope. This section contains troubleshooting instructions based on observed malfunctions
starting with generalized pressure problems and continuing to more specific malfunctions of compo-
nents and compressed air functions.
c. Test Equipment: Air pressure gage (0-200 psi min].
d. Troubleshooting. Troubleshooting procedures are given in table 9-1. The procedures are
grouped under the malfunctions listed below. Perform only those steps in a procedure required to
remedy the malfunction.
Insufficient air pressure (Malfunction No. 1).
Excessive system pressure indicated (Malfunction No. 2).
Park brakes will not release (Malfunction No. 3).
Trailer or towed vehicle brakes will not release (Malfunction No. 4).
Service brake will not release (one wheel only) (Malfunction No. 5).
Service brakes will not apply (Malfunction No. 6).
No service brakes on trailer or towed vehicle only (Malfunction No. 7).
Trailer hand control will not apply trailer service brakes (Malfunction No. 8).
Park brakes will not apply (Malfunction No. 9).
Service brakes are weak or slow responding (all wheels) (Malfunction No. 10).
Front service brakes are weak or slow responding (Malfunction No. 11).
Rear service brakes are uneven or erratic (Malfunction No. 12).
Service brakes are uneven or erratic on one or more wheels (Malfunction No. 13).
Brakes overheat (Malfunction No. 14).
Stop lamps do not operate, brakes function normally (Malfunction No. 15).
Pressure gage(s) not indicating or is not accurate, brakes normal (Malfunction No. 16.
Air horn does not operate (Malfunction No. 17).
Windshield wipers or washers are inoperative (Malfunction No. 18).
Interaxle differential lockup inoperative (Malfunction No. 19).