C7 and C9 On-Highway Engines Caterpillar

Use this procedure in order to troubleshoot the air inlet heater or use this procedure if any one of the diagnostic codes in Table 1 is active or logged.

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 ECM controls the operation of the air inlet heater and the ECM controls the operation of the lamp for the air inlet heater. The same technique for troubleshooting the primary circuit of the relay can be utilized for the lamp circuit.

Interaction of the Air Inlet Heater and the Starting Aid Output (Ether)

When the keyswitch is turned to the ON position, the air inlet heater will not be activated if the output of the starting aid is programmed to "Automatic", and if the inlet air temperature is below 0 °C (32 °F). The air inlet heater will not be activated when the starting aid circuit is activated.

When the output of the starting aid is programmed to "Automatic", the air inlet heater will not be activated until the engine is running and the starting aid output has been turned off for five seconds.

Effects of Vehicle Speed on the Operation of the Air Inlet Heater and on the Operation of the Brake Pedal Position

The air inlet heater is turned off when the brake pedal is depressed and the vehicle speed is equal to 8 km/h (5 mph) or greater than 8 km/h (5 mph).

If a diagnostic code for the vehicle speed sensor is active, the ECM will assume that the vehicle speed is above 8 km/h (5 mph). If an active diagnostic code is triggered for the vehicle speed sensor, the ECM will disable the heater when the brakes are applied.

The system has three modes of operation:

• 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 2, 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 progresses to the mode of engine cranking.

Mode of Engine Cranking

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. When the engine starts, the ECM proceeds to the mode of engine started.

Mode of Engine Started

After the engine has started, the mode will progress, as follows:

• 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. This concludes the operation of the heater until the keyswitch is cycled.

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 active 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.

Note: The coolant temperature and the intake manifold temperature are measured in degree Celsius. Caterpillar Electronic Technician (ET) can display the coolant temperature and the intake manifold temperature in °C or in °F. The ECM adds the coolant temperature and the intake manifold temperature together. Then, the ECM uses the sum of the coolant temperature and the intake manifold air temperature in order to determine if the air inlet heater should be on or off. Illustration 1 is a visual aid for troubleshooting the operation of the air inlet heater. The temperatures in °F are not a direct conversion of the temperatures in °C.

Illustration 1	g02081134
Operational chart for the air inlet heater

Illustration 2	g02071279
Schematic for the air inlet heater

Illustration 3	g02071280
Terminal locations at the P2 ECM connector for the air inlet heater (P2-5) Air inlet heater (P2-76) Return for the air inlet heater

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

The heating element is grounded with a braided ground strap. Check the condition of this component prior to troubleshooting a problem with the air inlet heater.

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect all of the connections for the air inlet heater. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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 for each ECM connector for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

5. Check the harness and wiring for abrasion and for pinch points from the air inlet heater back to the ECM and from the air inlet heater back to the battery.

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 harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - A problem has been found with a connector 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 Caterpillar 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 30 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: 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.

7. Return the wiring to the original configuration.

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 coil 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 P2-76. 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: The "Air Inlet Heater Override" has a one minute timer that disables the test when the time expires.

7. Stop the "Air Inlet Heater Override".

8. Turn the keyswitch to the OFF position.

9. Return the wiring to the original configuration.

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, "ECM - Replace".

  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 to the Air Inlet Heater Relay

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Illustration 6	g02081115
Typical example of the locations for the components (1) Connector for the air inlet heater lamp (2) Connector for the air inlet heater relay (3) Terminal of the air inlet heater relay to the heater (4) Terminal of the air inlet heater relay to +Battery (5) Air inlet heater relay (6) Test lamp (7) Connector (socket terminals)

Note: The heating element is grounded with a braided ground strap. Ensure that this strap is providing an adequate ground to a known good ground location.

1. Connect a test lamp between the +Battery side of the air inlet heater relay (4) and a known good ground location.

Expected Result:

The test lamp illuminates.

Results:

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

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

  Repair: Ensure that the OEM supplied fuse is not blown. There is an open circuit in the wiring between the battery and the air inlet heater 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 at the Terminal of the Air Inlet Heater Relay that is to the Heater.

1. Remove the wire to the heater from the air inlet heater relay at terminal (3) .

2. Connect a test lamp between the output terminal (3) of the air inlet heater relay and a known good ground.

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

3. Turn the keyswitch to the ON position.

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

   Note: 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.

6. Return the wiring to the original configuration.

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

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

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

  STOP

Test Step 7. Check for Voltage at the Air Inlet Heater

1. Remove the wire from the air inlet heater that comes from the air inlet heater relay.

2. Connect a test lamp between the wire that comes from the air inlet heater relay and engine ground.

3. Turn the keyswitch to the ON position.

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

   Note: 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.

6. Return the wiring to the original configuration.

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 wiring to the air inlet heater is OK. Proceed to Test Step 8.

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

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

  STOP

Test Step 8. Check the Wiring between the Air Inlet Heater and the Engine Ground

1. Remove the ground strap from the air inlet heater. Measure the resistance of ground strap to engine ground.

2. Return the wiring to the original configuration.

Expected Result:

The resistance measurement proves continuity of the circuit.

Results:

• OK - The resistance measurement proves continuity of the circuit. Proceed to Test Step 9.

• Not OK - There is an open circuit in the wiring for the ground strap.

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

  STOP

Test Step 9. Measure the Current through the Heating Element

1. Connect a 349-4199 AC/DC Current Probe or an equivalent inductive pickup clamp around the wire between the air inlet heater relay and the air inlet heater.

2. Turn the keyswitch to the ON position.

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

   Note: 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:

For 12 volt systems, the current reading is between 82 and 102 Amperes at a supply voltage of approximately 11 VDC.

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: Verify that the connections to the air inlet heater are making good contact. If the connections are OK, replace the heating element. Verify that the problem is resolved.

  STOP