C13 and C15 On-highway Engines Caterpillar

This procedure checks the circuits of the air inlet shutoff system for proper operation. The Engine Control Module (ECM) does not provide diagnostics for the circuits for the air inlet shutoff system.

Background Information

Certain engines are equipped with an air inlet shutoff system. The Electronic Control Module (ECM) activates the system in order to protect the engine from an overspeed condition. Typically, overspeed occurs if the engine takes in a large amount of combustible gases. The ECM activates the air inlet shutoff system for the following conditions:

Engine Overspeed - Engine speed exceeded 2500 rpm. The ECM energizes the air shutoff solenoid and fuel injection is disabled. A 2813-31 diagnostic code is activated. The ECM output for the air shutoff solenoid remains activated until the keyswitch is cycled. The engine's air shutoff mechanism may need to be manually reset in order to operate the engine after the mechanism is activated.

System Test - The operator can test the system in order to verify that the system is operating correctly. First, the overspeed verify switch is activated by the operator. Then, the operator increases the engine speed above 75 percent of the programmed overspeed setpoint. The ECM energizes the air shutoff solenoid and fuel injection is disabled. The ECM output for the air shutoff solenoid remains activated until the keyswitch is cycled. The engine's air shutoff mechanism may need to be manually reset in order to operate the engine after the mechanism is activated.

Note: If the "Air Shutoff" parameter is set to "Disabled", the system test remains operational. If the overspeed verify switch is activated during engine operation, the ECM disables fuel injection at any engine speed over 75 percent of the programmed overspeed setpoint. However, the ECM does not energize the air shutoff solenoid.

The "Air Shutoff" parameter must be set to "Enabled" in order for the ECM to energize the air shutoff solenoid.

The following components can cause problems with the air inlet shutoff system:

• Electrical connector or wiring

• Circuit component

• ECM

The most likely cause of a problem is a problem with an electrical connector or wiring. The least likely cause of a problem is the ECM.

Diagnostics on the Caterpillar Electronic Technician (ET)

"Air Inlet Shutoff System Control" Test - This test activates the air inlet shutoff system. This allows you to test the system for proper operation. The engine must be running in order to perform this test.

"Air Inlet Shutoff Relay Output" Test - This test activates the output for the air inlet shutoff system. This allows you to test the output for the air inlet shutoff relay. The engine must be stopped in order to perform this test.

For additional information regarding these tests, refer to the documentation that accompanies your Cat ET software.

Illustration 1	g01186366
Typical schematic diagram

Illustration 2	g01186370
Terminals on the ECM connectors (P1-3) Return (P1-46) Air inlet shutoff switch (P1-62) Neutral switch (P2-5) Air inlet shutoff relay (P2-76) Return

Test Step 1. Perform the "Air Inlet Shutoff System Control Test"

1. Turn the key switch to the OFF position.

2. Connect Cat ET to the service tool connector.

3. Turn the key switch to the ON position.

4. Place the transmission in neutral.

5. Start the engine. Increase the engine speed to 1500 rpm ± 100 rpm.

6. Access the "Air Inlet Shutoff System Control Test" in the "Diagnostic Tests" under the "Diagnostics" menu on Cat ET.

7. Start the test.

8. Wait for the engine to stop.

9. Stop the test.

Expected Result:

Fuel injection is disabled. The air inlet shutoff is activated and the engine is shutdown.

Results:

• OK - The engine is shutdown when the "Air Inlet Shutoff System Control Test" is activated. The air inlet shutoff is working correctly.

  Repair: Reset the air inlet shutoff system.

  Proceed to Test Step 2.

• Not OK - The engine did not shut down. Proceed to Test Step 4.

Test Step 2. Check the Air Inlet Shutoff Switch

1. Turn the key switch to the ON position.

2. Monitor the status for the air inlet shutoff switch while the switch is depressed.

Expected Result:

The status is "On" when the switch is depressed. The status is "Off" when the switch is released.

Results:

• OK - The switch is operating correctly. The air inlet shutoff system is working properly.

  STOP

• Not OK - The switch is not operating correctly. Proceed to Test Step 3.

Test Step 3. Check the Circuit to the Air Inlet Shutoff Switch

1. Turn the key switch to the OFF position.

2. Remove the air inlet shutoff switch.

3. Turn the key switch to the ON position.

4. Monitor the status for the air inlet shutoff switch while the two wires from the switch are connected.

Expected Result:

The status is "On" when the wires are connected. The status is "Off" when the wires are disconnected.

Results:

• OK - The indications are correct. The wiring is OK. The switch is not working properly.

  Repair: Replace the air inlet shutoff switch.

  Verify that the repair eliminates the problem.

  STOP

• Not OK - The indications are not correct. There is a problem with the wiring between the ECM and the air inlet shutoff switch.

  Repair: Inspect the wiring between the ECM and the air inlet shutoff switch. Repair the wiring or replace the wiring. Verify that the repair eliminates the problem.

  STOP

Test Step 4. Check the Interlock for the Air Inlet Shutoff

Verify that P1-62 is connected to the +Battery.

Note: J1/P1-62 is used for the transmission neutral switch. If a transmission neutral switch is installed, the transmission must be in neutral.

Expected Result:

P1-62 is connected to the +Battery or the transmission is in neutral.

Results:

• OK - P1-62 is connected to the +Battery.

  Repair: Check the status for the "Transmission Neutral Switch" while the transmission is in neutral. The status should be "On". If the status is "Off", refer to Troubleshooting, "Neutral Switch Circuit - Test".

  Proceed to Test Step 5.

• Not OK - P1-62 is not connected to the +Battery.

  Repair: Connect P1-62 to the +Battery.

  Repeat Test Step 1.

Test Step 5. Inspect Electrical Connectors and Wiring

1. Turn the key switch to the OFF position.

2. Thoroughly inspect the J2/P2 ECM connector and all other connectors in the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on the wires that are associated with the air inlet shutoff system.

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

5. Check the harness and wiring for abrasion and for pinch points from the components back to the ECM.

Expected Result:

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

Results:

• OK - All the wires and connections are OK. Proceed to Test Step 6.

• Not OK - There is a problem with the wiring.

  Repair: Perform the following 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 6. Perform the "Air Inlet Shutoff Relay Output" Test

1. Turn the key switch to the OFF position.

2. Turn the key switch to the ON position. Do not start the engine.

3. Access the "Air Inlet Shutoff Relay Output" test on Cat ET.

4. Start the test and listen for a click from the relay for the air inlet shutoff.

Expected Result:

The relay is active.

Results:

• OK - A click is heard. The relay is active. Proceed to Test Step 7.

• Not OK - A click is not heard. There is a problem with the relay circuit. Proceed to Test Step 9.

Test Step 7. Check the Supply Voltage to the Air Inlet Shutoff Solenoid

Illustration 3	g00850138
Typical air inlet shutoff solenoid

1. Turn the key switch to the ON position.

2. Access the "Air Inlet Shutoff Relay Output" test on Cat ET.

3. Use a voltage test lamp to check the voltage across the two terminals of the air inlet shutoff solenoid.

4. Activate the "Air Inlet Shutoff Relay Output" test.

   Note: The output for the air inlet shutoff will be active for one second.

Expected Result:

The voltage test lamp illuminates when the test is active.

Results:

• OK - The voltage test lamp illuminates when the test is active. The ECM is properly controlling the relay for the air inlet shutoff solenoid, but the air inlet shutoff solenoid is not working. Proceed to Test Step 8.

• Not OK - The voltage test lamp does not illuminate when the test is active. The air inlet shutoff solenoid is not receiving the correct signal. Proceed to Test Step 12.

Test Step 8. Check the Resistance of the Solenoid

1. Disconnect the wires from the air inlet shutoff solenoid.

2. Measure the resistance of the air inlet shutoff solenoid.

3. Connect the wires to the air inlet shutoff solenoid.

Expected Result:

The resistance is between 15 Ohms and 20 Ohms.

Results:

• OK - The resistance of the air inlet shutoff solenoid is OK.

  Repair: Check electrical connections. Refer to Troubleshooting, "Electrical Connectors - Inspect" for more information.

  STOP

• Not OK - The resistance of the solenoid is incorrect.

  Repair: Replace the air inlet shutoff solenoid.

  Verify that the repair eliminates the problem.

  STOP

Test Step 9. Check the Resistance of the Relay

1. Turn the key switch to the OFF position.

2. Unplug the air inlet shutoff relay.

3. Measure the resistance between the terminals on the relay's connector.

Expected Result:

The resistance is between 5 Ohms and 10 Ohms.

Results:

• OK - The resistance of the relay is OK. Proceed to Test Step 10.

• Not OK - The resistance is incorrect.

  Repair: Replace the relay.

  Verify that the repair eliminates the problem.

  STOP

Test Step 10. Check the Signal Voltage to the Relay

1. Turn the key switch to the ON position.

2. Access the "Air Inlet Shutoff Relay Output" test on Cat ET.

3. Check the voltage across the relay's solenoid with a voltage test lamp.

   Note: The output for the air inlet shutoff system will be active for only one second.

4. Activate the "Air Inlet Shutoff Relay Output" test.

Expected Result:

The voltage test lamp illuminates when the test is active.

Results:

• OK - The voltage test lamp illuminates when the test is active. The relay is receiving the signal from the ECM. Proceed to Test Step 11.

• Not OK - The voltage test lamp does not illuminate when the test is active. The relay is not receiving the signal from the ECM. Proceed to Test Step 13.

Test Step 11. Check the Power Supply to the Relay

Measure the voltage between the +Battery terminal of the relay and the engine ground.

Expected Result:

The voltage is approximately equal to the battery voltage.

Results:

• OK - The voltage is approximately equal to the battery voltage. The relay is receiving power. Proceed to Test Step 12.

• Not OK - The voltage is not approximately equal to the battery voltage. There is a problem in the wiring between the relay and the +Battery terminal.

  Repair: Repair the circuit.

  Verify that the repair eliminates the problem.

  STOP

Test Step 12. Check the Output Voltage of the Relay

1. Ensure that all of the circuit's connectors are connected.

2. Turn the key switch to the ON position.

3. Access the "Air Inlet Shutoff Relay Output" test on Cat ET.

4. Check the voltage from the output terminal on the relay to the engine ground with a voltage test lamp.

   Note: The output for the air inlet shutoff system will be active for only one second.

5. Activate the "Air Inlet Shutoff Relay Output" test.

Expected Result:

The voltage test lamp illuminates when the test is active.

Results:

• OK - The voltage test lamp illuminates when the test is active. There is a problem in the wiring between the relay and the air inlet shutoff solenoid.

  Repair: Repair the circuit.

  Verify that the repair eliminates the problem.

  STOP

• Not OK - The voltage test lamp does not illuminate when the test is active. The relay is not sending power to the air inlet shutoff solenoid.

  Repair: Replace the relay for the air inlet shutoff relay. Verify that the repair eliminates the problem.

  STOP

Test Step 13. Check for Shorts in the Wiring Harness between the Relay and the ECM

1. Ensure that the key switch is in the OFF position.

2. Disconnect the J2/P2 ECM connectors.

3. Disconnect the air inlet shutoff relay.

4. Measure the resistance between terminals P2-5 and P2-76.

Expected Result:

The resistance is an open circuit.

Results:

• Yes - The resistance is an open circuit. The wiring does not have a short circuit. Proceed to Test Step 14.

• No - The resistance is not an open circuit. There is a problem in the wiring harness between the ECM and the relay.

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

  STOP

Test Step 14. Check the Relay Signal at the ECM

1. Turn the key switch to the OFF position.

2. Remove the terminals from P2-5 and P2-76.

3. Turn the key switch to the ON position.

4. Check the voltage between terminals P2-5 and P2-76 with a voltage test lamp.

   Note: The output for the air inlet shutoff system will be active for only one second.

5. Activate the "Air Inlet Shutoff Relay Output" test on Cat ET.

6. Turn the key switch to the OFF position.

7. Return the wiring to the original configuration.

Expected Result:

The voltage test lamp illuminates when the test is active.

Results:

• OK - The ECM is supplying the correct voltage. There is an open circuit in the harness.

  Repair: Repair the circuit.

  Verify that the repair eliminates the problem.

  STOP

• Not OK - The ECM is not supplying the correct voltage.

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

  Verify that the repair eliminates the problem.

  STOP