Troubleshooting the Air Brake System on the M1090 LMTV Dump Truck. Whenever the brake pedal is held depressed, the brake system continually dumps air from somewhere in the rear of the truck. Eventually the system pressure drops enough for the warning screamer to come on. In this video, I trouble shoot and rebuild the Haldex Air Brake Relay Valve using common rebuild kit Part number 12417375-001 or 2530-01-478-5902