3126B Petroleum Engine Caterpillar

The Electronic Control Module (ECM) has the ability to stop the engine by shutting off the inlet air supply in an emergency situation. The ECM activates a relay which energizes the air shutoff solenoid. The solenoid trips the air shutoff valve.

There are two conditions which can cause the ECM to activate the air shutoff relay. The first condition occurs when the ECM detects an engine overspeed. The relay will be energized until the ECM detects an engine speed of 0 rpm. The second condition occurs when a test of the air shutoff relay is made. The overspeed verify switch is activated. When the engine speed reaches 75 percent of the programmed overspeed setpoint, the ECM will activate the air shutoff relay. Again, this is used for testing purposes.

The air shutoff valve must be manually reset to the OPEN position.

Verify that the air shutoff system has been installed. Verify that the parameter for "Air Shutoff" has been programmed to "ON" on the configuration screen of the CaterpillarElectronic Technician (ET). If the "Air Shutoff" is not programmed, Cat ET will display "Disabled" on the status screen.

Illustration 1	g00743757
Schematic for the air shutoff system

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The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.

2. Verify that the air shutoff valves are set to the Open position.

3. Thoroughly inspect the J1/P1 ECM connector and the P61 customer connector. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 2	g01102047
P1 terminals that are associated with the air shutoff system (P1-11) Air shutoff solenoid (P1-54) Overspeed verify switch (P1-67) Solenoid common

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Illustration 3	g01123348
J61/P61 terminals that are associated with the air shutoff system (4) Air shutoff solenoid (5) Solenoid common (40) Overspeed verify switch

4. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the air shutoff system.

5. Check the allen head screw on the ECM connectors and the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

6. Check the harness and the wiring for abrasion and for pinch points from the air shutoff solenoid to the ECM.

Expected Result:

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

Results:

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

• Not OK - The connectors and/or wiring are not OK.

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly connected. Verify that the problem is resolved.

  STOP

Test Step 2. Test for Voltage from the Normally Open Contacts of the Air Shutoff Relay

1. Turn the keyswitch to the OFF position.

2. Remove the wire from the normally open contacts of the air shutoff relay that goes to the air shutoff solenoid.

3. Connect a 8T-0500 Continuity Test Light between the normally open contact of the air shutoff relay and engine ground.

4. Start the engine.

5. Activate the overspeed verify switch.

6. Monitor the test light while you increase the engine speed past 75 percent of the programmed overspeed setpoint.

7. Turn the keyswitch to the OFF position.

8. Disconnect the test light's leads. Connect the wire to the normally open contact.

Expected Result:

The test light illuminated when the engine speed increased past 75 percent of the programmed overspeed setpoint.

Results:

• OK - The test light illuminated. The air shutoff relay is operating correctly. Proceed to Test Step 3.

• Not OK - The test light did not illuminate. Proceed to Test Step 4.

Test Step 3. Test for Voltage at the Air Shutoff Solenoid

1. Turn the keyswitch to the OFF position.

2. Disconnect the wires that are connected to the coil of the air shutoff solenoid.

3. Connect a 8T-0500 Continuity Test Light between the wire from the normally open contact of the air shutoff relay and engine ground.

4. Start the engine.

5. Activate the overspeed verify switch.

6. Monitor the test light while you increase the engine speed past 75 percent of the programmed overspeed setpoint.

Expected Result:

The test light illuminated when the engine speed increased past 75 percent of the programmed overspeed setpoint.

Results:

• OK - The test light illuminated. The voltage is present at the air shutoff solenoid.

  Repair: Verify the continuity of the wire from the air shutoff solenoid to the negative battery before proceeding. Replace the air shutoff solenoid. Verify that the problem is resolved.

  STOP

• Not OK - The test light did not illuminate. System voltage was not present at the air shutoff solenoid. There is a problem in the wiring between the air shutoff solenoid and the air shutoff relay. There may be a problem with a connector.

  Repair: Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 4. Test for Voltage at the Coil of the Air Shutoff Relay

1. Turn the keyswitch to the OFF position.

2. Disconnect the wire that carries the drive signal from the ECM to the air shutoff relay. Disconnect the wire at the coil of the air shutoff relay.

3. Connect the 8T-0500 Continuity Test Light between the end of the wire and engine ground.

4. Start the engine.

5. Activate the overspeed verify switch.

6. Monitor the test light while you increase the engine speed past 75 percent of the programmed overspeed setpoint.

Expected Result:

The test light illuminated when the engine speed increased past 75 percent of the programmed overspeed setpoint.

Results:

• OK - The test light illuminated. Verify the continuity of the wire from the coil of the air shutoff relay to the ECM connector P1-67 before proceeding. Proceed to Test Step 6.

• Not OK - The test light did not illuminate. The voltage from the ECM was not present at the coil of the air shutoff relay. Proceed to Test Step 5.

Test Step 5. Short the Overspeed Verify Switch at the ECM

1. Turn the keyswitch to the OFF position.

2. Disconnect ECM connector P1.

3. Remove terminal P1-54 (overspeed verify switch).

4. Insert one end of a wire jumper into the socket for P1-54 (overspeed verify swtich). Connect the other end of the wire jumper to engine ground.

5. Remove terminal P1-11 (air shutoff solenoid).

6. Insert one end of the wire jumper into the socket for P1-11 (air shutoff solenoid).

7. Connect one lead of a 8T-0500 Continuity Test Light to the other end of the jumper wire in P1-11 (air shutoff solenoid).

8. Connect the other lead of the test light to negative battery.

9. Start the engine.

10. Activate the overspeed verify switch.

11. Monitor the test light while you increase the engine speed past 75 percent of the programmed overspeed setpoint.

Expected Result:

The test light illuminated when the engine speed increased past 75 percent of the programmed overspeed setpoint.

Results:

• OK - The test light illuminated.

  Repair: Verify the continuity of the wire for the overspeed verify switch to the negative battery. Close the overspeed verify switch and measure the continuity from P1-54 to the negative battery. If the wire does not have continuity to the negative battery, repair the wire and/or replace the overspeed verify switch.If the wire for the overspeed verify switch has continuity to the negative battery, there is a problem in the wiring between P1-11 and the air shutoff relay. Repair the circuit connectors or wiring and/or replace the circuit connectors or wiring. Verify that the problem is resolved.

  STOP

• Not OK - The test light did not illuminate.

  Repair: Perform the following procedure:

  1. Remove all jumpers and reconnect all terminals.

  2. Temporarily install a new ECM. Refer to Troubleshooting, "Replacing the ECM".

  3. Check the system for active diagnostic codes.

  4. Perform this Test Step again.

  5. If the problem is resolved with the test ECM, reconnect the suspect ECM. Verify that the problem returns. If the problem returns with the suspect ECM, replace the ECM. Verify that the problem is resolved.

  STOP

Test Step 6. Test the Diode for Current Flow in One Direction

Illustration 4	g00761537
Diode

1. Disconnect the wires from the air shutoff relay.

2. Remove the diode from the air shutoff relay.

3. Put the digital voltmeter (DVM) in "Diode Check".

4. Refer to Illustration 4. Place the red lead of the DVM on the diode at location (A). Place the black lead of the DVM on the diode at location (B).

5. Measure the voltage drop across the diode.

Expected Result:

The voltage drop across the diode is less than one volt.

Results:

• OK - The voltage drop across the diode is less than one volt. Proceed to Test Step 7.

• Not OK - The voltage drop across the diode is greater than one volt.

  Repair: Replace the diode. Verify that the problem is resolved.

  STOP

Test Step 7. Test the Diode for Current Flow in the Opposite Direction

1. Reverse the locations of the leads for the DVM.

2. Measure the voltage drop across the diode.

Expected Result:

The voltage drop across the diode is an OL.

Results:

• OK - The voltage drop across the diode is an OL. Proceed to Test Step 8.

• Not OK - The voltage drop across the diode is less than one volt.

  Repair: Replace the diode. Verify that the problem is resolved.

  STOP

Test Step 8. Check the Voltage from the Keyswitch to the Normally Open Contacts of the Air Shutoff Relay

1. Turn the keyswitch to the OFF position.

2. Disconnect the wire to the normally open contacts of the air shutoff relay from the keyswitch.

3. Connect a 8T-0500 Continuity Test Light between the wire and engine ground.

4. Turn the keyswitch to the ON position.

Expected Result:

The test light illuminates.

Results:

• OK - The test light illuminated.

  Repair: Replace the air shutoff relay. Verify that the problem is resolved.

  STOP

• Not OK - The test light did not illuminate. Proceed to Test Step 9.

Test Step 9. Check the Voltage from the Keyswitch to the Air Shutoff Relay

1. Turn the keyswitch to the OFF position.

2. Remove the wire from terminal R of the keyswitch.

3. Turn the keyswitch to the ON position.

4. Measure the voltage between terminal B of the keyswitch and engine ground.

5. Measure the voltage between terminal R of the keyswitch and engine ground.

6. Turn the keyswitch to the OFF position.

Expected Result:

Voltage is present on terminal B and terminal R at the keyswitch.

Results:

• OK - Voltage is present on terminal B and terminal R at the keyswitch.

  Repair: If voltage is present on terminal R, repair the wire between the keyswitch and the air shutoff relay. Verify that the breaker is not tripped. Return all wiring to the original configuration. Verify that the problem is eliminated.

  STOP

• Not OK - Voltage is not present on terminal B at the keyswitch.

  Repair: If voltage is not present on terminal B, repair the wire between the +Battery and the keyswitch. Verify that the breaker is not tripped. Verify that the battery disconnect switch is operating correctly. Check the battery's no-load voltage. Return all wiring to the original configuration. Verify that the problem is eliminated.

  STOP

• Not OK - Voltage is not present on terminal R at the keyswitch.

  Repair: If voltage is present on terminal B of the keyswitch but not present on terminal R, replace the keyswitch. Return all wiring to the original configuration. Verify that the problem is eliminated.

  STOP