3500B Engines for 5130B and 5230B Excavators Caterpillar

The throttle switch provides the operator with the ability to select the desired engine speed. Engine speed will decrease with increasing load. The throttle switch is a rotary switch with ten positions.

The throttle switch is connected to the four throttle inputs of the ECM. Each position generates a specific on/off pattern on the throttle inputs. A diagnostic code is generated if a pattern that does not correspond with any of the switch positions is detected.

Once a diagnostic code is generated, the ECM ignores the throttle input signals and desired engine speed is set to the last valid pattern that was recognized by the ECM. Also, the Automatic Engine Speed Control (AESC) is enabled until the ECM is turned off and desired engine speed may be toggled between low idle and high idle by operating the AESC enable switch. Desired engine speed is set to low idle while the engine is not running.

Voltage at the throttle inputs to the ECM should be 11.5 ± 0.5 VDC when the throttle inputs are open. The voltage should be less than 0.5 VDC when the throttle inputs are closed.

Illustration 1	g00815394
Typical schematic

Test Step 1. Inspect Electrical Connectors and Wiring.

1. Turn the keyswitch to the OFF/RESET position.

2. Thoroughly inspect ECM connector J1/P1, machine connector J3/P3, and the throttle switch connector J118/P118. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

3. Check the harness and wiring for corrosion, abrasion, and pinch points from the throttle switch to the ECM.

Expected Result:

All connectors, pins, and sockets should be completely inserted and coupled. The harness and wiring should be free of corrosion, abrasion, and pinch points.

Results:

• OK - All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, abrasion, and pinch points. Proceed to Test Step 2.

• Not OK - All connectors, pins, and sockets are not completely inserted and coupled. The harness and wiring are not free of corrosion, abrasion, and pinch points.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

Test Step 2. Check the "Throttle Cab Switch Position" on ET.

1. Connect ET at the service tool connector.

2. Turn the keyswitch to the ON position.

3. Observe the status of the throttle switch and the throttle inputs on ET while you operate the throttle switch in each position.

Expected Result:

The status on ET should correspond with the information in Table 1.

Results:

• OK - The throttle switch is functioning properly at this time.

  Repair: Refer to Troubleshooting, "Inspecting Electrical Connectors" if the problem is intermittent.

  Stop.

• Not OK - Record the suspect input. Proceed to Test Step 3.

Test Step 3. Jumper the Switch Input at the Throttle Switch Connector.

1. Disconnect the throttle switch connector J118/P118.

2. Observe the status of the suspect throttle input on ET.

3. Use a suitable piece of wire to short P118-1 (Digital Return) to the terminal for the suspect throttle input at the throttle switch connector P118.

4. Observe the status of the suspect throttle input on ET.

5. Remove the wire short.

Expected Result:

The status of the suspect throttle input should be "Off" when the throttle switch connector J118/P118 is disconnected. The status should be "On" when the wire short is installed.

Results:

• OK - The harness and the ECM are okay.

  Repair: Replace the throttle switch.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The ECM did not get the correct signal. There is a problem in the harness. Proceed to Test Step 4.

Test Step 4. Check for Shorts in the Harness.

1. Turn the keyswitch to the OFF/RESET position.

2. Disconnect ECM connector J1/P1 and the throttle switch connector J118/P118.

3. Measure the resistance between engine ground and the terminal for the suspect throttle input at the throttle switch connector P118.

4. Measure the resistance between the terminal for the suspect throttle input at the throttle switch connector P118 and the remaining terminals at the connector.

Expected Result:

The resistance should be greater than 20,000 Ohms for each reading.

Results:

• OK - The resistance is greater than 20,000 Ohms for each reading. Proceed to Test Step 5.

• Not OK - The resistance is less than 20,000 Ohms for each reading. There is a short in the harness between the ECM and the throttle switch.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

Test Step 5. Check the Resistance through the Harness.

1. Use a suitable piece of wire to short P118-1 (Digital Return) to the terminal of the suspect throttle input at the throttle switch connector P118.

2. Measure the resistance between P1-29 (Digital Return) and the terminal for the suspect throttle input at ECM connector P1.

Expected Result:

The resistance should be less than 10 Ohms.

Results:

• OK - The resistance is less than 10 Ohms. Proceed to Test Step 6.

• Not OK - The resistance is greater than 10 Ohms. There is an open circuit or excessive resistance in the harness.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

Test Step 6. Check the Harness and the ECM.

1. Turn the keyswitch to the OFF/RESET position.

2. Disconnect ECM connector J1/P1 and remove the wire for the suspect throttle input from ECM connector P1.

3. Reconnect all connectors.

4. Turn the keyswitch to the ON position.

5. Observe the status of the suspect throttle input on ET.

6. Turn the keyswitch to the OFF/RESET position.

7. Disconnect ECM connector J1/P1 and remove the wire from P1-29 (Digital Return).

8. Fabricate a jumper wire with pins at both ends. Insert the jumper wire at P1-29 (Digital Return) and the suspect throttle input at ECM connector P1.

9. Reconnect all connectors.

10. Turn the keyswitch to the ON position.

    Note: Additional diagnostic codes will be generated because P1-29 (Digital Return) will no longer be connected to other sensors and switches. Ignore the codes and clear the codes when you complete this test.

11. Observe the status of the suspect throttle input on ET.

12. Turn the keyswitch to the OFF/RESET position.

13. Remove the jumper wire from ECM connector P1 and reconnect all wires and connectors.

Expected Result:

The status of the suspect throttle input should be "Off" when the throttle input is open. The status should be "On" when the jumper wire (short) is installed.

Results:

• OK - There is a problem in the harness between the ECM and the throttle switch.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The switch signal appears at the ECM. The ECM is not reading the switch properly.

  Repair: Verify your results. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.

  Stop.