Air valve leaking air thru it when u release tractor parking brake 1999 379 Peterbilt

Why ?
Programmer Description
The heater and A/C programmer is attached to a bracket. The bracket is located next to the right end of the heating, ventilation, and air conditioning (HVAC) module assembly, behind the glove box. The heater and A/C programmer provides the controls for temperature regulation.
The heater and A/C programmer controls an electric actuator. The electric actuator adjusts the air mix valve position in order to blend cold and warm air. Vehicles with dual zone (CJ2) have 2 electric actuators that mix the air independently of each other. The motor is reversible and moves a rotary shaft which drives the air mix valve link. The motor also provides a position sensor signal in order to monitor the actual valve position.
The heater and A/C programmer operates the 4 vacuum solenoids. The solenoids control vacuum to the various vacuum actuators. The vacuum actuators control the following components:
• The air inlet valve
• The A/C DEFROST valve
• The UP/DOWN valve
The heater and A/C programmer also controls the park brake release actuator. The powertrain control module (PCM) sends a Class 2 serial data message to the heater and A/C programmer whenever the transmission is shifted out of PARK or NEUTRAL. The heater and A/C programmer will then supply vacuum to the park brake release solenoid, which releases the park brake.
The heater and A/C programmer sometimes is referred to as the air control module (ACM). This reference is commonly used by a scan tool and by the diagnostic trouble codes (DTCs).
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if it has a belt driven air compressor check belt and tension
it could be a buzzer problem
it could be an air leak in the system ( possible in the park brake diaphragms )
install an air gauge in the drain plug of a tank and monitor the air pressure use
with the truck being driven normally then the tank pressure should not show much variation
test the brake system by tuning the engine off, hold and apply the foot brake and see if the pressure continues to diminish indicating a leak in the system or foot valve operation
finally take it back to nissan ud as it will be still under warranty

when you release the brakes (pushing in yellow and red release buttons) ,tp1and tp2 do the rods in the chambers retract in to cans, ? where is the air going ? you may want to just crack 1 line at a time to see and follow air as it moves from tractor to trailer , no chance glad hands are reversed ? are your slack adjusters moving?are air tanks full 120-150 psi ?what happens when you manually retract slacks,that should cause rod to go into can , are brakes in very good condition ?(lining,springs,"S" cams and bushings drums ), you said you replaced valves does that include quick release valves (QR1) and relay valves ? did you also change anti compounding valve ?what happens when you push on brakes and dash valves are released ,where is the air going , do you think there's any problems with ABS if equipped ? if you manually retract brakes (using lock out devices or keys ) do brakes release , PLEASE don't get mad when you read this I'm just giving things to think of , I have done 100's of truck and trailer brakes , and it sounds like you did every thing and then some to try to get it to work . I really hope I helped you . Woody.

by releasing the park brake you are in fact putting air in the park brake (spring brake diaphragms) that compresses the springs and allows the brakes to release. When you apply the park brake you are in effect dumping the air out of the system and allowing the spring brakes to come on. The light is telling you that there is insufficient air in the park brake circuit to fully release the spring brakes. Some ideas are that the air lines on the trailer are opposite to the prime mover(tractor), there is a kink in the air lines in the trailer , the air tank that holds emergency air for the spring brakes system has an internal leak in a valve between chambers or externally between air tanks. I would make very sure that I fixed this problem before I travelled as the consequences of a trailer wheel lock up at speed could have very serious results.

valve might be stuck

check out the brake light switch either under the dash at the top of the brake pedal or on the brake valve body. It is probably stuck in the on position

This sounds like a vacuum leak. Possibly at the brake booster. There is a check valve on the vacuum booster. Check it by pulling it out and see if you can blow thru it both ways. Air should flow freely in one direction and NO air passing thru the other way.

may have a small air leak or faulty pressure sensor

96 F & B Series

Air Brake System, FT Series



Item Part Number Description 1 2025 Front Brake Chamber 2 2A095 Quick Release Valve 3 2075 Compressor 4 2085 Governor 5 2A783 Tank Valve 6 2A550 Safety Valve 7 2063 Air Tank Reservoir 8 2A567 Drain **** 9 2B170 Single Check Valve 10 2K119 Double Check Valve 11 18737 Low Pressure Indicator 12 2A270 Foot Control Valve (E-7) 13 13480 Stoplamp Switch 14 2A662 Parking Brake Control Valve (PP-1) 15 2B280 Chassis Bulkhead Manifold 16 2B431 Inverting Relay Valve (R-7) 17 2A449 Relay Valve (R-12) 18 2225 Rear Brake Chamber A — 3/8-Inch Hose B — 1/4-Inch Hose C — 1/2-Inch Hose D — 5/8-Inch Hose

5 Inspect Brake Fluid Type Brake fluid loss or contamination 10 Inspect Master Cylinder (Brake System) Worn or leaking brake master cylinder. 11 Inspect Brake Power Booster Damaged booster vacuum line/check valve, or diaphram