Brakes - Brake Pressure Switch DTC C1939 Addition
Bulletin No: 04-006/02Last Issued: 12/11/2002
Subject:
BRAKE PRESSURE SWITCH / DEACTIVATOR SWITCH CIRCUIT FAILURE DIAGNOSIS C1939
APPLICABLE MODEL(S)/VINs
All 2001-2003 Truck with 4WABS
DESCRIPTION
DTC C1939 is missing from 2001-2003 workshop manual. C1939 is for an open or short circuit in the Brake Pressure Switch (BPS).
The BPS serves two purposes; first, it is an input to the ABS control module to indicate that pressure exists in the Brake Master Cylinder, second, it is a back up input to the PCM for cruise control, it indicates the brake pedal has been pressed in addition to the Brake On Off (BOO) switch. (For cruise control the Brake Pressure Switch is sometimes referred to as the Deactivator Switch).
The BPS is a normally closed switch. It provides a B+ signal to the ABS control module, this switch opens circuit momentarily when the brake pedal is pressed hard.
REPAIR PROCEDURE
Customers experiencing DTC C1939 should have their vehicles repaired using the procedure shown.
BRAKE PRESSURE SWITCH REMOVAL/INSTALLATION
1. Disconnect the Brake Pressure Switch electrical connector N-138
2. Remove the Brake Pressure Switch
3. Fill the new Brake Pressure Switch with High Performance DOT 3 Brake fluid
4. Install the Brake Pressure Switch into the Brake Master Cylinder
5. Torque the Brake Pressure Switch to 17 Nm (13 lb-ft)
6. Connect the Brake Pressure Switch electrical connector N-138
7. Bleed the brake system see Workshop Manual Section 04 BRAKE SYSTEM BLEEDING 04-11-1
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