3500B Industrial Engines with the ADEM 3 Electronic Control Module Caterpillar

The intermediate speed switch is a normally open switch. When this switch is closed, the engine speed will decrease to the customer programmable intermediate idle speed. This intermediate speed is the speed rate of the PTO. This will happen regardless of PTO set speed or the desired speed for the throttle position sensor. When the intermediate speed switch is opened, the engine speed will be increased back to the desired engine speed for the throttle or the desired engine speed for PTO operation according to the ramp rate for the PTO speed. If the intermediate idle speed is programmed above the current desired engine speed for the throttle or the desired engine speed for PTO operation, this switch will have no effect on engine speed.

Illustration 1	g01266225
Typical schematic

Illustration 2	g01266226
P1 connector for the Electronic Control Module (ECM) (P1-5) Digital return (P1-27) Input for the intermediate speed switch

Illustration 3	g01234146
Location of ECM connectors

Illustration 4	g01266229
Machine interface connector (Terminal 09) Digital return (Terminal 28) Input for the intermediate speed switch

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.

2. Turn the breaker for the ECM to the OFF position.

3. Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors in the circuit. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the proper procedure for inspecting system wiring.

4. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

5. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

6. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The harness and wiring are OK. Proceed to Test Step 2.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Status of the Intermediate Speed Switch on Caterpillar Electronic Technician (ET)

1. Connect Cat ET to the service tool connector.

2. Turn the breaker for the ECM to the ON position.

3. Turn the switch that provides power to the keyswitch input for the ECM to the ON position.

4. Operate the intermediate speed switch. Observe the status for the intermediate speed switch on Cat ET.

Expected Result:

The status of the intermediate speed switch reads "ON" with the intermediate speed switch in the ON position. The status of the intermediate speed reads "OFF" when the intermediate speed switch is in the OFF position.

Results:

• OK - The circuit for the intermediate speed switch is operating normally.

  Repair: If an intermittent condition is suspected, refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The circuit for the intermediate speed switch is not operating normally. Proceed to Test Step 3.

Test Step 3. Check the Intermediate Speed Switch

1. Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.

2. Turn the breaker for the ECM to the OFF position.

3. Remove the wires from the terminals on the intermediate speed switch.

4. Connect a voltmeter between terminal 2 and terminal 3 on the intermediate speed switch.

5. Measure the resistance between terminal 2 and terminal 3 on the intermediate speed switch.

6. Turn the intermediate speed switch to the ON position.

7. Measure the resistance between terminal 2 and terminal 3 on the intermediate speed switch.

Expected Result:

The resistance measurement indicates an open circuit with the intermediate speed switch in the OFF position. The resistance measurement indicates a short circuit with the intermediate speed switch in the ON position.

Results:

• OK - The resistance measurements are OK. The problem is not with the intermediate speed switch. Proceed to Test Step 4.

• Not OK - The resistance measurements are not OK. The intermediate speed switch is not operating correctly.

  Repair: Replace the intermediate speed switch. Verify that the problem is no longer present.

  STOP

Test Step 4. Check for a Short Circuit in the Wiring Harness

1. Disconnect the ECM connector J1/P1.

2. Measure the resistance between P1-05 and the engine ground.

3. Measure the resistance between P1-05 and every terminal on ECM connectors P1 and P2.

4. Measure the resistance between P1-27 and the engine ground.

5. Measure the resistance between P1-27 and every terminal on ECM connectors P1 and P2.

Expected Result:

The resistance measurements for P1-27 indicate an open circuit. The resistance measurements for P1-05 indicate an open circuit except for terminals P1-23 and P1-28.

Note: Terminals P1-23 and P1-28 are connected to terminal P1-05 through the emergency stop switch.

Results:

• OK - The resistance measurements are OK. Proceed to Test Step 5.

• Not OK - The resistance measurements are not OK. There is a short in the harness between the intermediate speed switch and the ECM.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the problem is no longer present.

  STOP

Test Step 5. Check the Wiring Harness for an Open Circuit

1. Short the wires from the intermediate speed switch together at the intermediate speed switch.

2. Measure the resistance between P1-05 and P1-27 at the ECM connectors.

3. Replace all wires and remove all shorts.

Expected Result:

The resistance measurement indicates a short circuit.

Results:

• OK - The resistance measurement indicates a short circuit. Proceed to Test Step 6.

• Not OK - The resistance measurement does not indicate a short circuit. There is an open or excessive resistance in the wires or connectors between the intermediate speed switch and the ECM.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the problem is no longer present.

  STOP

Test Step 6. Check the Operation of the ECM

1. Disconnect the ECM connector J1/P1.

2. Remove the wire for the intermediate speed switch from ECM connector P1-27. Install a wire jumper into the socket for P1-27. Ensure that the wire jumper is isolated from engine ground and any other wires.

3. Turn the breaker for the ECM to the ON position.

4. Turn the switch that provides power to the keyswitch input for the ECM to the ON position.

5. Observe the status of the intermediate speed switch on Cat ET.

6. Fabricate a jumper wire.

   Connect the wire jumper in socket P1-27 to the digital return at socket P1-5.

7. Observe the status of the intermediate speed switch on Cat ET.

8. Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.

9. Turn the Battery switch for the ECM to the OFF position.

10. Replace all wires to the original configuration.

Expected Result:

The status of the intermediate speed switch is OFF when the wire jumper is isolated. The status of the intermediate speed switch changes to ON when the wire jumper is shorted to the digital return.

Results:

• OK - The status of the intermediate speed switch is correct. The ECM is operating correctly.

  Repair: Check the connectors for damage, looseness or corrosion. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The ECM is not reading the inputs from the intermediate speed switch correctly.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP