3126B Engine for Lexion 450, Lexion 460, and Lexion 460 R Combines Air Inlet Heater Circuit - Test Caterpillar

System Operation Description:

Use the following information in order to check the operation of the air inlet heater and the air inlet heater relay.

The following background information is related to the operation of the air inlet heater:

The air inlet heater is used to improve the ability of the engine to start when the engine is cold. A reduction of white smoke and reduced emission levels are also benefits of the air inlet heater.

The Electronic Control Module (ECM) controls the operation of the air inlet heater and the ECM controls the operation of the lamp for the air inlet heater through the air inlet heater relay.

The operation of the air inlet heater is determined by three different cycle times:

• Mode of powerup and preheat

• Mode of engine cranking

• Mode of engine started

Mode of Powerup and Preheat

Regardless of temperature, the heater and the lamp for the heater will be activated for two seconds when the ECM is first powered (lamp check).

The ECM then calculates the sum of the coolant temperature plus the intake manifold air temperature. This sum must be below the following temperature in order for the air inlet heater to be activated prior to engine cranking:

If the sum of the temperatures is below the temperature that is mentioned in Table 1, the air inlet heater will be activated for a maximum of 30 seconds during the preheat cycle.

If the operator attempts to start the engine prior to the completion of preheat, the ECM reverts to the mode of engine cranking.

Mode of Engine Cranking

During engine cranking, the ECM first checks if the coolant temperature is less than 0 °C (32 °F). If this condition is true, the ECM activates the heater during engine cranking.

If the preceding condition is false, the ECM calculates the sum of the coolant temperature plus the intake manifold air temperature. This sum must be below the following temperature in order for the air inlet heater to be activated during engine cranking:

If either of the preceding conditions are true, the ECM will activate the heater until the engine starter is disengaged. If the engine fails to start, the ECM reverts to the mode of powerup and preheat. If the engine starts the ECM proceeds to the mode of engine started.

Mode of Engine Started

After the engine has started, the same combination of intake manifold air temperature and coolant temperature will determine the state of the heater. The cycle has two strategies:

• Continuous operation

• Intermittent operation

Continuous Operation

During continuous operation of the air inlet heater, the heater may operate continuously for a maximum of seven minutes after the engine has started. The ECM will exit the mode of continuous operation early if the sum of the coolant temperature plus the intake manifold air temperature exceeds the following temperatures:

When this temperature is exceeded the air inlet heater is turned off and the mode of engine started is completed.

If the temperatures for the preceding strategy are not met in seven minutes, the strategy for intermittent operation will be performed.

Intermittent Operation

During the strategy for intermittent operation, the ECM cycles the power to the air inlet heater in ten second intervals.

This strategy will be effective for a maximum of 13 minutes after the strategy has begun. The ECM will exit the mode of intermittent operation early if the sum of the coolant temperature plus the intake manifold air temperature exceeds the following temperatures:

When this temperature is exceeded, the ECM shuts off the air inlet heater until the keyswitch is cycled.

If there is an active diagnostic code for the coolant temperature sensor or the intake manifold air temperature sensor, the following strategy will be used:

Coolant Temperature Sensor

If there is an active diagnostic code for the coolant temperature sensor, all temperature conditions will rely solely on the air inlet temperature sensor. All temperature conditions will be satisfied at an air inlet temperature of 10 °C (50 °F) at all altitudes.

Air inlet Temperature Sensor

If there is an active diagnostic code for the air inlet temperature sensor, all temperature conditions will rely solely on the coolant temperature sensor. All temperature conditions will be satisfied at a coolant temperature of 40 °C (104 °F) at all altitudes.

Illustration 1	g01351393
Schematic for the air inlet heater

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.
   Show/hide table

   Illustration 2	g01351533
   Location of the components that are related to the air inlet heater (typical left side engine view) (1) Air inlet heater relay (2) Air inlet heater (3) J2/P2 ECM connectors

2. Thoroughly inspect all of the connections for relay (1) and for heater element (2). Also, thoroughly inspect ECM connectors (3). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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   Illustration 3	g01351538
   (P2-9) Return for the air inlet heater (P2-12) Air inlet heater

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   Illustration 4	g01155187
   Terminal locations at the connector for the air inlet heater (Terminal 1) Air inlet heater (Terminal 2) Return for the air inlet heater

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the air inlet heater.

4. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and the wiring for abrasion and for pinch points from the ECM to each electrical component that is associated with the air inlet heater.

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 harnesses and the wiring appear to be 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 for Active Diagnostic Codes

1. Connect AVSpare Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Turn the keyswitch to the ON position.

3. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 15 seconds so that any codes may become active.

   Look for these codes:

   • 617-5

   • 617-6

4. Turn the keyswitch to the OFF position.

Expected Result:

No diagnostic codes are active for the air inlet heater.

Results:

• OK - Neither of the above codes are active. There may be a problem with the secondary circuit for the air inlet heater. Proceed to Test Step 5.

• Not OK - At least one of the codes that are listed above are active. A 617-5 or 617-6 diagnostic code is active. There is a problem in the control circuit for the air inlet heater. Proceed to Test Step 3.

Test Step 3. Check for a Control Input Voltage at the Relay

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Illustration 5	g01118589
Small terminals for the typical air inlet heater relay

1. Disconnect the wires from the small terminals of the air inlet heater relay.

2. Install a test lamp across the wires.

3. Turn the keyswitch to the ON position.

4. Start the "Air Inlet Heater Override" on Cat ET and observe the test lamp.

   Note: Do not leave the "Air Inlet Heater Override" on for an extended period of time. This will prevent unnecessary cycling of the air inlet heater and the battery from discharging. The "Air Inlet Heater Override" has a one minute timer that disables the test when the time expires.

5. Stop the "Air Inlet Heater Override".

6. Turn the keyswitch to the OFF position.

Expected Result:

The test lamp illuminates while the override is active.

Results:

• OK - The test lamp illuminates while the override is active. There is a problem in the control circuit of the relay.

  Repair: Replace the air inlet heater relay. Clear any diagnostic codes. Verify that the problem is resolved.

  STOP

• Not OK - The test lamp did not turn on while the override was active. There is a problem in the harness or in a connector from the ECM to the air inlet heater relay. There may be a problem with the ECM. Return the wiring to the original configuration. Proceed to Test Step 4.

Test Step 4. Check for Proper Operation of the ECM

1. Disconnect the J2/P2 ECM connectors.

2. Fabricate two jumper wires that are long enough to create a test circuit at the ECM connector. Crimp connector sockets to one end of each of the jumper wires.

3. Remove the wires from terminal locations P2-5 and P2-79. Install a jumper wire into each of these terminal locations.

4. Connect the J2/P2 ECM connectors.

5. Fasten the leads of the test lamp onto the ends of the jumper wires.

6. Start the "Air Inlet Heater Override" on Cat ET and observe the test lamp.

   Note: Do not leave the "Air Inlet Heater Override" on for an extended period of time. This will prevent unnecessary cycling of the air inlet heater and the battery from discharging. The "Air Inlet Heater Override" has a one minute timer that disables the test when the time expires.

7. Return the wiring to the original configuration.

8. Turn the keyswitch to the OFF position.

Expected Result:

The test lamp illuminates while the override is active.

Results:

• OK - The test lamp illuminates while the override is active.

  Repair: The ECM is operating correctly. The problem is in the harness or in a connector between the ECM and the air inlet heater relay. Check the resistance of the wiring in the harness in order to isolate the problem. Repair the harness and/or the connectors. Replace parts, if necessary. Verify that the repair eliminates the original problem.

  STOP

• Not OK - The test lamp did not illuminate while the override was active.

  Repair: There is a problem with the ECM. Perform the following procedure:

  1. Temporarily connect a test ECM.

     Refer to Troubleshooting, "Replacing the ECM".

  2. Recheck the circuit in order to ensure that the original problem has been resolved.

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

     If the problem is not resolved with the test ECM, install the original ECM. There is a problem in the wiring.

  STOP

Test Step 5. Check for Battery Voltage at the Relay

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Illustration 6	g01338483
Location of the +Battery side of the air inlet heater relay

1. Connect a test lamp between the +Battery side of the air inlet heater relay and the engine ground.

Expected Result:

The test lamp illuminates.

Results:

• OK - The test lamp illuminates. Battery voltage is reaching the relay. Proceed to Test Step 6.

• Not OK - The test lamp does not illuminate. Battery voltage is not present at the relay.

  Repair: Verify that the fuse is not blown.

  If the fuse is not blown, there is an open circuit in the wiring between the battery and the relay. There may be a problem with a connector.

  Repair the wire and/or the connector. Replace parts, if necessary. Verify that the original problem has been resolved.

  STOP

Test Step 6. Check for Voltage Output at the Relay

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Illustration 7	g01338505

1. Connect a test lamp between the output terminal of the air inlet heater relay and the engine ground stud.

   Note: Observe the test lamp. The test lamp will be off, since the relay is not energized. If the test lamp is on, ensure that the test lamp is connected to the output side of the relay.

2. Turn the keyswitch to the ON position.

3. Activate the "Air Inlet Heater Override" on Cat ET and observe the test lamp.

   Note: Do not leave the "Air Inlet Heater Override" on for an extended period of time. This will prevent unnecessary cycling of the air inlet heater and the battery from discharging. The "Air Inlet Heater Override" has a one minute timer that disables the test when the time expires.

4. Stop the "Air Inlet Heater Override" and turn the keyswitch to the OFF position.

Expected Result:

The test lamp illuminated when the "Air Inlet Heater Override" was enabled.

Results:

• OK - The test lamp illuminated when the "Air Inlet Heater Override" was enabled. The air inlet heater relay is operating correctly. Proceed to Test Step 7.

• Not OK - The test lamp did not illuminate when the "Air Inlet Heater Override" was enabled.

  Repair: There is a problem with the air inlet heater relay. Replace the relay. Verify that the problem is resolved.

  STOP

Test Step 7. Check the Wiring Between the Relay and the Heating Element and Between the Heating Element and the Engine Ground

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Illustration 8	g01352812
Top side engine view (4) Supply wire for the heating element (5) Ground strap for the heating element

1. Isolate wire (4) that is between the relay and the heating element. Measure the resistance of the wire that connects the relay to the air inlet heater.

2. Isolate ground strap (5). Measure the resistance of ground strap.

Expected Result:

Both of the resistance measurements prove continuity of the circuit.

Results:

• OK - Both of the resistance measurements prove continuity of the circuit. There is not an open circuit in the wiring for the heating element. Restore the wiring to the original configuration. Proceed to Test Step 8.

• Not OK - There is an open circuit in the wiring for the heating element.

  Repair: Repair the wire and/or the ground strap. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 8. Measure the Current through the Heating Element

1. Connect a 155-5176 AC/DC Current Probe or an equivalent inductive pickup clamp around wire (1) between the relay and the air inlet heater.

2. Connect the current probe to a multimeter.

3. Turn the keyswitch to the ON position.

4. Run the "Air Inlet Heater Override" on Cat ET and observe the current reading on the multimeter.

   Note: Do not leave the "Air Inlet Heater Override" on for an extended period of time. This will prevent unnecessary cycling of the air inlet heater and the battery from discharging. The "Air Inlet Heater Override" has a one minute timer that disables the test when the time expires.

5. Stop the "Air Inlet Heater Override" and turn the keyswitch to the OFF position.

Expected Result:

For 12 volt systems, the current reading is between 82 and 102 Amperes. The voltage reading is approximately 11 VDC.

For 24 volt systems, the current reading is between 77 and 95 Amperes. The voltage reading is approximately 22 VDC.

Note: If the voltage reading does not match the specified value, you will need to adjust the current value accordingly. For slightly lower voltages, the current value will be slightly lower. For slightly higher voltages, the current value will be slightly higher.

Results:

• OK - The readings are within the specified ranges.

  Repair: The readings are within the specified ranges. The air inlet heater circuit appears to be operating correctly at this time. There may be an intermittent problem in one of the circuits for the air inlet heater. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information on troubleshooting intermittent electrical problems.

  STOP

• Not OK - The voltage reading and/or the current reading is not within the specified ranges.

  Repair: Replace the heating element. Verify that the problem is resolved.

  STOP