D250E Series II, D300E Series II, D350E Series II and D400E Series II Articulated Trucks Power Train Electronic Control System Caterpillar

Illustration 1	g00483661
Schematic Of The Pressure Switch For The Service Brake

This diagnostic code is recorded when the ECM reads the voltage of the service brake (wire 720-BU) as being above normal for seven hours continuously during machine operation.

The possible causes of this diagnostic code are listed:

• There is an open in wire (J764-PU). The open is between the switch and the return contact (J1-15).

• The switch is faulty.

• Wire 720-PU is open between the switch and the ECM (J1-24).

• The ECM is faulty. This is unlikely.

The results of this diagnostic code are listed:

• The indicator for the service brake on the display is NEVER ON.

• When the service brake is being applied, the downshift points do not occur at a RPM that is higher than normal. The elevated shift function does not operate.

1. CHECK THE SWITCH.

   1. Turn the disconnect switch and the key start switch to the ON position.

   2. Ensure that the diagnostic code is active.

   3. Disconnect the switch from the machine harness.

   4. Install a jumper wire between the signal wire (720-PU) and the return wire (J764-BR) at the pressure switch.

      Expected Result: The diagnostic code changes from being active to being NOT active as the jumper is installed and then removed.

      Results:

      • OK - The diagnostic code changes from active to NOT active as the jumper wire is installed and then removed. The pressure switch is failed. Repeat this test "CHECK THE SWITCH" in order to verify that the switch has failed. Replace the service brake pressure switch. STOP.

      • NOT OK - The diagnostic code remains active. The diagnostic code does NOT change. The machine harness is faulty or the ECM is faulty. Proceed to 2.

2. CHECK FOR AN OPEN CIRCUIT.

   1. Remove the jumper wire of the previous test "CHECK THE SWITCH".

   2. Turn the key start switch and the disconnect switch to the OFF position.

   3. Disconnect the J1 and J2 machine harness connectors from the ECM.

   4. At the pressure switch, install a jumper wire from the signal wire (720-PU) to frame ground.

   5. At the pressure switch, install a jumper wire from the return wire (J764-BR) to frame ground.

   6. At the J1 machine harness connector for the ECM, measure the resistance from contact J1-24 (wire 720-PU) to frame ground.

   7. At the J1 machine harness connector for the ECM, measure the resistance from contact J1-15 (wire J764-BR) to frame ground.

      Expected Result: Each resistance measurement should measure less than 5000 ohms.

      Results:

      • OK - Each resistance measurement is less than 5000 ohms. Proceed to 3.

      • NOT OK - One or both resistance measurements is NOT less than 5000 ohms. There is an open in the machine harness. The open is in the wire (s) with the high resistance measurement. Repair the machine harness or replace the machine harness. Verify that the diagnostic code is no longer active. STOP.

3. CHECK FOR A SHORT TO +BATTERY.

   1. The key start switch and the disconnect switch remain in the OFF position.

   2. Remove all jumper wires that were previously installed.

   3. The J1 and J2 machine harness connectors remain disconnected from the ECM.

   4. At the J1 machine harness connector for the ECM, measure the resistance from the signal contact J1-24 (wire 720-PU) to all possible sources of positive voltage. The sources of positive voltage are contacts: J1-1 (wire 126-PK), J1-4 (wire A958-WH), J1-6 (wire 126-PK), J1-8 (wire 306-GN), J1-10 (wire 728-BU), J1-11 (wire 705-PK), J1-12 (wire 703-BU), J1-17 (wire 904-BU), J1-18 (wire 704-GY), J2-1 (wire K746-PK), J2-2 (wire 368-OR), J2-7 (wire G870-GY), J2-8 (wire K745-YL), J2-13 (wire G705-GN), J2-19 (wire G704-YL) and J2-37 (wire 321-BR).

      Expected Result: The resistance for each measurement should be greater than 5000 ohms.

      Results:

      • OK - Each resistance measurement is greater than 5000 ohms. The harness is correct. The pressure switch is failed. Replace the pressure switch and verify that the new pressure switch corrects the problem. If the diagnostic code remains exit this procedure. It is unlikely that the ECM is faulty. Perform this diagnostic code procedure again. If the cause of the diagnostic code is not found, replace the ECM. See Testing And Adjusting, "Electronic Control Module (ECM) - Replace". STOP.

      • NOT OK - Each resistance measurement is NOT greater than 5000 ohms. The machine harness is faulty. There is a short in the machine harness. The short is between the signal wire (720-PU) and the wire with the low resistance measurement. Repair the machine harness or replace the machine harness. STOP.