thanks for the info. do you have an schematic you can send me

DTC 523859-4 - Service Brake Pressure OORL
A. SENSOR SUPPLY OPEN CIRCUIT
B. SENSOR SIGNAL OPEN CIRCUIT
C. SENSOR SIGNAL SHORTED TO SENSOR GROUND
D. SENSOR SIGNAL SHORTED TO FRAME GROUND
E. SENSOR FAILURE
F. FUNCTIONAL FAILURE IN CONTROLLER
CAUSE A - SENSOR SUPPLY OPEN CIRCUIT
PROCEDURE OR ACTION:
1. Ensure truck power is OFF.
2. Disconnect indicated sensor connector.
3. Turn truck power ON.
4. Change DMM to volts scale.
5. At sensor harness connector, measure voltage across sensor supply pin (+) and sensor ground pin ( ).
Is voltage approximately 5 Vdc?
YES: Sensor supply circuit is OK. Go to Cause B.
NO: Go to Step 6.
6. Move negative ( ) meter probe to a clean frame ground.
Is voltage approximately 5 Vdc?
YES: Sensor ground has open circuit. Locate and repair/replace open wire/connection. See Wire Harness
Repair 2200 SRM 1128.
NO: Sensor supply has open circuit. Locate and repair/replace open wire/connection. See Wire Harness Repair
2200 SRM 1128.
CAUSE B - SENSOR SIGNAL OPEN CIRCUIT
PROCEDURE OR ACTION:
1. Ensure truck power is OFF.
2. Disconnect indicated sensor connector.
3. Change DMM to ohms scale. Verify DMM zero reading.
4. At sensor harness connector, measure resistance between sensor signal pin and sensor ground pin.
Is resistance approximately equal to the resistor value shown in applicable schematic?
YES: Go to Cause F.
NO: If resistance measurement is infinite, sensor signal wire has open circuit. Locate and repair/replace open
wire/connection. See Wire Harness Repair 2200 SRM 1128. If resistance measurement is less than 0.5 ohms,
go to Cause C.
CAUSE C - SENSOR SIGNAL SHORTED TO SENSOR GROUND
PROCEDURE OR ACTION:
1. Disconnect indicated sensor connector and VSM/ECU/GCU connector.
2. At the sensor harness connector, measure resistance between sensor signal pin and sensor ground pin.
Is resistance less than 0.5 ohms?
YES: Sensor signal wire is shorted to sensor ground wire. Locate and repair/replace shorted wire/connector.
See Wire Harness Repair 2200 SRM 1128.
NO: Go to Cause D.
CAUSE D - SENSOR SIGNAL SHORTED TO FRAME GROUND
PROCEDURE OR ACTION:
1. At the sensor harness connector, measure resistance between sensor signal pin and a clean frame ground on
truck.
Is resistance less than 0.5 ohms?
YES: Sensor signal wire is shorted to frame ground. Locate and repair/replace shorted wire/connector. See
Wire Harness Repair 2200 SRM 1128.
NO: Go to Cause E.
CAUSE E - SENSOR FAILURE
PROCEDURE OR ACTION:
NOTE: For the FAP sensor use a pressure gauge to check that the LPG Pressure Regulator has not failed. See
Electrical System 2200 SRM 1142.
1. Ensure truck power is OFF.
2. Replace sensor.
NOTE: Do not discard original sensor after removal.
3. Ensure that all connections are completely inserted.
4. Turn truck power ON.
Does reported DTC reoccur?
YES: Reinstall original sensor and go to Cause F. See Electrical System 2200 SRM 1142.
NO: Problem has been corrected. Resume operation. Discard faulty sensor.
CAUSE F - FUNCTIONAL FAILURE IN CONTROLLER
PROCEDURE OR ACTION:
1. Ensure all previous procedures have been completed.
2. Ensure truck power is OFF.
3. Ensure that all connections to the controller are completely inserted.
4. Ensure truck power is OFF for no less than 30 seconds, and then to ON to clear displayed DTC.
Does reported DTC reoccur?
YES: Go to Step 5.
NO: Problem corrected. Resume operation.
5. At the DSC, press ENTER to access Main Menu.
6. Scroll to VIEW VERSIONS, press ENTER.
7. Scroll to TRUCK SERIAL NUMBER, press ENTER.
8. View the TRUCK SERIAL NUMBER on the display.
Does the truck serial number on display match serial number on truck nameplate (VSM Only)?
YES: Go to Step 9.
NO: Controller has been substituted from another truck. Replace VSM with VSM that has the correct truck serial
number or obtain new VSM with correct Serial number/ CDF. See Electrical System 2200 SRM 1142.
9. Resident Service Approval Required prior to VSM replacement for Trucks under warranty. Make sure
to indicate the DTC code(s) on the warranty claim and include an accurate problem description leading to the
controller replacement.
10. For other controllers, Replace indicated controller.(ECU-ECM/GCU/TCU). See Electrical System 2200 SRM
1142. For GM 4.3L LPG engines, see LPG Fuel System, GM 4.3L Engine 900 SRM 1242. For GM 4.3L
gasoline engines, see Gasoline Fuel System, GM 4.3L Engine 900 SRM 1244 for all controllers.
11. Reinstall all removed components and ensure that all connectors are completely inserted.
12. Repeat Component Operational Check.