G3520B Industrial Engines Caterpillar

Use this procedure to troubleshoot a suspected problem with the circuit that is for the speed control. Use this procedure if one of the diagnostic codes in Table 1 is active or easily repeated.

Note: For this troubleshooting procedure, the "Desired Speed Input" configuration parameter must be set to "4-20 mA Input" in the "Service/Configuration" screen of the Caterpillar Electronic Technician (ET). Do not select "PWM". The master ECM cannot be configured to accept a Pulse Width Modulated signal (PWM) for speed control for the engine.

The selection of the "4-20 mA Input" setting requires a 4 to 20 mA signal for regulation of the desired engine speed. Do not use this procedure if the "Desired Speed Input" is set to "0-5 VDC Input".

When the desired speed input is correspondingly configured, the master ECM controls the engine speed according to the 4 to 20 mA current.

The value of the current corresponds to a range of desired engine speeds between minimum high idle and maximum high idle. The "Minimum Engine High Idle Speed" and the "Maximum Engine High Idle Speed" are set with the "Service/Configuration" screen of Cat ET. For more information, refer to Troubleshooting, "Configuration Parameters".

When the idle/rated speed switch is in the RATED position, a current value of 4.0 mA corresponds to the programmed "Minimum Engine High Idle Speed". A current value of 20.0 mA corresponds to "Maximum Engine High Idle Speed". Current values within this range will vary the desired engine speed in a linear fashion. The values will vary between "Minimum Engine High Idle Speed" and "Maximum Engine High Idle Speed".

The most likely causes of a diagnostic code for this circuit are a poor connection or a problem in a wiring harness. The next likely cause is a problem with a component. The least likely cause is a problem with the master ECM.

Illustration 1	g01586196
Schematic of the circuit for the 4 to 20 mA desired speed input

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Set the engine control to the OFF/RESET position. Remove the electrical power from the engine.

Show/hide table



Illustration 2	g01414551
Location of the connectors at the terminal box that are for the speed control (1) J1/P1 ECM connectors at the master ECM (2) J5/P5 customer connectors (3) J10/P10 connectors for the advisor monitor display

Show/hide table



Illustration 3	g01461289
Location of the potentiometer for the desired speed at the engine display panel (4) Speed potentiometer

2. Thoroughly inspect the condition of connectors (1) , (2) , and (3) . Also, thoroughly inspect the electrical condition and the mechanical condition of speed control device (4) . Refer to Troubleshooting, "Electrical Connectors - Inspect".

Show/hide table



Illustration 4	g01414564
Terminal locations at the P1 ECM connector that are associated with the speed control (P1-36) Desired speed (4-20 mA) (P1-37) Return

Show/hide table



Illustration 5	g01414576
Terminal locations at the P5 ECM connector that are associated with the speed control (P5-20) Desired speed (4-20 mA) (P5-21) Return

Show/hide table



Illustration 6	g01414586
Terminal locations at the P10 connector that are associated with the speed control (P10-E) Desired speed (4-20 mA) (P10-J) Return

3. Perform a 45 N (10 lb) pull test on each of the wires in the circuit for the speed control.

4. Check the torque of the allen head screws for each of the ECM connectors and of the customer connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and the wiring for abrasion and for pinch points from the terminal box to the advisor monitor display.

Expected Result:

All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

  Repair: Perform the necessary repairs and/or replace parts, if necessary.

  STOP

Test Step 2. Check for Active Diagnostic Codes

1. Connect Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Restore the electrical power to the engine. Turn the engine control to the STOP position.

3. While you adjust the speed control from the minimum speed to the maximum speed, monitor the active and logged diagnostic codes on Cat^® ET. Wait at least 30 seconds in order for diagnostic codes to become active. Look for the following active diagnostic codes:
   • 524-3 Desired Engine Speed Sensor : Voltage Above Normal

   • 524-4 Desired Engine Speed Sensor : Voltage Below Normal

4. Set the engine control to the OFF/RESET position. Remove the electrical power from the engine.

Expected Result:

None of the above diagnostic codes became active during the test.

Results:

• OK - No diagnostic codes were activated.

  Repair: The output for the speed control appears to be OK. The initial diagnostic code may have been caused by a poor electrical connection. If an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect", for information that is related to troubleshooting intermittent electrical problems.

  STOP

• Active 524-3 Code - A 524-3 diagnostic code became active while you adjusted the speed control. The ECM has detected an excessive amperage in the circuit for the speed control. Proceed to Test Step 3.

• Active 524-4 Code - A 524-4 diagnostic code became active while you adjusted the speed control. The ECM has detected a low amperage in the circuit for the speed control. Proceed to Test Step 5.

Test Step 3. Check the Wiring for an Open Circuit

1. Ensure that the engine control is in the OFF/RESET position. Ensure that the electrical power is removed from the engine and the speed control device.

2. Remove the wires for the desired speed and the return from the speed control device that supplies the 4 to 20 mA signal.

3. Install a jumper wire between the wires for the desired speed and the return on the speed control device.

4. Disconnect the P1 connector from the master ECM.

5. Measure the resistance between terminals P1-36 and P1-37 at the ECM connector.

Expected Result:

The circuit is continuous.

Results:

• OK - The circuit is continuous. There is not an open circuit in the wiring for the speed control. Do not connect the J1/P1 ECM connectors. Remove the jumper wire. Do not connect the speed control device to the circuit. Proceed to Test Step 4.

• Not OK - The measurement indicates that there is excessive resistance in the circuit.

  Repair: There is excessive resistance in the circuit for the speed control. There is a problem with a connector and/or with the wiring between the P1 connector and the speed control device. Repair the connection and/or the wire, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 4. Check the Wiring for a Short Circuit to the +Battery

1. Ensure that the engine control is in the OFF/RESET position. Ensure that the electrical power is removed from the engine and the speed control device.

2. At each of the electrical wires that have been removed from the speed control device, use a multimeter to check for a voltage. Check the voltage between the loose wire and the negative battery contact for the engine.

3. Return electrical power to the engine. Turn the engine control to the STOP position.

4. Again at each of the electrical wires that have been removed from the speed control device, use a multimeter to check for a voltage. Check the voltage between the loose end of the wires and the negative battery contact that is for the engine.

5. Ensure that the engine control is in the OFF/RESET position. Ensure that the electrical power is removed from the engine and the speed control device.

Expected Result:

The circuit measures zero V at the wires for the speed control device.

Results:

• OK - The circuit measures zero V at the wires for the speed control device. The circuit is not shorted to the +Battery in the harness. Proceed to Test Step 5.

• Not OK - The voltage measurement is greater than zero V at the wires that are for the speed control device.

  Repair: There is a short to the +Battery in the harness or in a connector. Repair the connection and/or the wire, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 5. Check the Wiring for a Short Circuit to Engine Ground

1. Ensure that the loose ends of the wires at the speed control device do not create a short circuit to ground.

2. Measure the resistance between the ground strap for the master ECM and terminal P1-37 at the ECM connector.

Expected Result:

The resistance measurement shows that the circuit is not continuous.

Results:

• OK - The resistance measurement shows that the circuit does not have continuity to the ground source.

  Repair: The signal wire for the speed control is not shorted to engine ground. Reconnect the P1 ECM connector. Reconnect the wiring for the 4 to 20 mA signal at the speed control device.

  Proceed to Test Step 6.

• Not OK - The resistance measurement shows that there is continuity between the signal wire and the ground source.

  Repair: There is a problem with a connector and/or with the harness that is for the speed signal to the master ECM. Locate the wire with the short circuit and replace the wire. Verify that the problem is resolved.

  STOP

Test Step 6. Check the Device that Provides the 4 to 20 mA Signal

Measure the 4 to 20 mA signal according to the literature that is provided by the OEM of the device. Verify that the correct signal is being provided to the master ECM.

Verify the correct 4 to 20 mA signal at terminals P1-36 and P1-37 for the master ECM.

Expected Result:

The correct 4 to 20 mA signal is provided to the master ECM.

Results:

• OK - The correct 4 to 20 mA signal is provided to the master ECM.

  Repair: The ECM is receiving the correct signal, but the ECM is not responding correctly to the signal. There appears to be a problem with the master ECM. Perform the following procedure:

  1. Turn the engine control to the OFF/RESET position. Remove the electrical power from the engine.

  2. Temporarily install a new ECM. Refer to Troubleshooting, "ECM - Replace" for details.
  If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Verify that the original problem has been resolved.

  STOP

• Not OK - The master ECM is not receiving the correct 4 to 20 mA signal.

  Repair: There is probably a problem with the device that provides the 4 to 20 mA. Service the device that provides the 4 to 20 mA according to the literature that is provided by the OEM of the device.

  STOP