3408E and 3412E Engines for Caterpillar Built Machines Caterpillar

The throttle switch provides the operator with the ability to select the desired engine speed. The throttle switch is a backlit momentary rocker switch. This switch is located near the right armrest of the operator's seat.

At engine start-up, engine speed is set to low idle. For high idle operation, the operator must momentarily depress the throttle switch in the forward direction without depressing the decelerator pedal. To return to low idle, the operator can momentarily depress the throttle switch in the backward direction. Desired engine speed can be set and maintained by performing the following steps:

• Set the engine to high idle by momentarily depressing the throttle switch in the forward direction.

• Achieve the desired engine speed by depressing the decelerator pedal. Maintain the position of the decelerator pedal.

• Set the desired engine speed by depressing the throttle switch in the forward direction for two seconds.

The desired engine speed is now set. The decelerator pedal will function with a range between the set engine speed and low idle.

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. If the engine is being operated above 1000 rpm, the ECM will drop the engine speed to 1000 rpm. If the engine is being operated below 1000 rpm, the ECM will maintain the current engine speed.

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	g00712704
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. Refer to Troubleshooting, "Electrical Connectors - Inspect" 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 - Proceed to Test Step 2.

• Not OK -

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

  STOP

Test Step 2. Check the Status 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, "Electrical Connectors - Inspect" 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.

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

3. Use a suitable piece of wire to short terminal 2 (Digital Return) to the terminal for the suspect throttle input at the throttle switch connector.

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

5. Move the wire short from terminal 2 (Digital Return) to terminal 5 (Digital Return) of the throttle switch connector.

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

7. Remove the wire short.

Expected Result:

The status of the suspect throttle input should be "Off" when the throttle switch connector is disconnected. The status should be "On" when the wire short is installed. The status should not change when the wire short is moved from terminal 2 to terminal 5.

Results:

• OK - The harness and the ECM are OK.

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

  STOP

• Not OK - 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.

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

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

Expected Result:

Resistance should be greater than 20,000 for each reading.

Results:

• OK - Proceed to Test Step 5.

• Not OK - 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 Resistance through the Harness

Illustration 2	g00666871
ECM connector P1 (ECM side)

1. Use a suitable piece of wire to short terminal 5 (Digital Return) to the terminal of the suspect throttle input at the throttle switch connector.

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

Expected Result:

Resistance should be less than 10 Ohms.

Results:

• OK - Proceed to Test Step 6.

• Not OK - 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

Illustration 3	g00666991
ECM connector P1 (wire side)

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 sockets 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