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-PU) as being below normal for two hours continuously while the machine is in operation.

The possible causes of this diagnostic code are listed:

• The switch is faulty.

• Wire 720-PU is shorted to ground 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 ALWAYS ON.

• The transmission will shift more than normal or the transmission will hunt because the function for the turn around shift operates all the time.

• The downshift points occur at a higher level than normal RPM because the elevated shift function operates all the time.

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 A SHORT TO GROUND.

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

   2. Remove all jumper wires that were previously installed.

   3. Disconnect the J1 and J2 machine harness connectors 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 ground. The sources of ground are contacts: J1-2 wire (202-BK), J1-5 wire (202-BK), J1-7 wire (F789-PU), J2-3 wire (F790-PK) and frame ground.

      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.