SFN-20240118B Replace pressure switch

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TICO Document #: SFN-20240118B (formerly TES 139)

Description of Procedure: If you are having problems with the direction change feature where the vehicle will not change when a range is selected with your brake pedal depressed, replace the pressure switch with a dual circuit switch that works with the logic of both TCM and ECM programming.

Units Affected: Some units with Allison Gen V transmissions controls and Cummins QSB-IVi & 2015-ISB engines.

Parts Required: Switch, Dual Circuit N/O – N/C, 4 PSI Set Press, 91236 (QTY 1)

Reducer, 1/4” – 1/8” NPT 40813 (QTY 1)

Planned Labor: 20 minutes

Instructions:

  1. Park vehicle on flat surface, apply parking brake, and chock wheels. If your company utilizes a “Lock Out, Tag Out” policy, you should employ it during this procedure.

  2. Release all pressure from the air system by releasing the drain valve on the air tanks. This will apply the parking brake.

  1. Raise the cab to its full upright position. Ensure the cab latch bracket is engaged and is supporting the cab.

  1. Locate the pressure switch on the underneath side of the cab floor. Switch in mounted in the brake valve. (Reference Fig. 1 and Fig. 2)

  1. Remove the electrical connections from the pressure switch and then the pressure switch from the brake valve port.

  1. Apply Loctite 565 pipe sealant to the threads of the 1/4” – 1/8” NPT Reducer (40813) and pressure switch (91236).

  1. Install both in brake valve, in the previous port that you just removed the old switch from.

  1. Connect EE44 (Green) to the “N/C” switch post. Connect TR122 (Yellow) to the “N/O” switch post. Connect EE62 (White) and TR103 (White) to the “C” switch post. (Reference Fig. 3 Schematic).

  1. Lower the cab to its normal operating position.

  1. Start engine and build up air system to 120 PSI. Apply brake pedal an check for leaks. This can be done by using a squirt bottle with water and soap solution.

  1. With parking brake applied engine at low idling, check function of the gear selector. From “Neutral”, check forward gear range and reverse gear range. Selector should flash but not obtain a gear range. Now repeat with your brake pedal slightly depressed. Transmission now should shift into gear range selected.

  1. Remove “Lock Out, Tag Out” plaque.

  1. Return vehicle to service.