3126E On-highway Engine Caterpillar

This procedure can also be used to troubleshoot the following components:

• The air inlet heater

• The air inlet heater relay

• The lamp for the air inlet heater

The air inlet heater is used in order to improve the engine's ability to start when the engine is cold. The air inlet heater also reduces white smoke at start-up.

The 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:

• ECM Powerup and Preheat Cycle

• Cranking

• Engine Started

The cycle time is determined by the following items:

• Engine parameters

• Vehicle speed

• Service brake

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 ECM Powerup and Preheat Cycle.

The lamp for the air inlet heater should turn on for a minimum of 2 seconds when the ECM is first powered up. The lamp should turn on regardless of the coolant temperature. The ECM will signal the air inlet heater to stay on for 30 seconds if the sum of the coolant temperature and the inlet manifold air temperature is less than 25 degrees Celsius or 109 degrees Fahrenheit.

The air inlet heater and the lamp for the air inlet heater should turn on. The air inlet heater and the lamp for the air inlet heater should turn off when the cycle is complete.

The ECM will control the air inlet heater during engine cranking if the operator starts the engine before the end of the heating cycle.

Control of the Air Inlet Heater During Engine Cranking

If the sum of the coolant temperature and the inlet manifold air temperature is less than 25 degrees Celsius or 109 degrees Fahrenheit, the air inlet heater will turn on when the engine is cranking. The heater will remain on while the engine is cranking. The air inlet heater will reactivate for 30 seconds if the engine fails to start.

Engine Start Cycle

The operation of the air inlet heater is determined by the coolant temperature and the inlet manifold air temperature after the engine has started. If the combined temperature is less than 25 degrees Celsius or 109 degrees Fahrenheit, the engine start cycle begins. The engine start cycle has two segments:

• Continuous Mode

• On/Off Cycling Mode

The Continuous Mode lasts for a maximum of seven minutes. The On/Off Cycling Mode can last for a maximum of thirteen minutes. The air inlet heater is turned on and the air inlet heater is turned off for ten seconds during the On/Off Cycling Mode. The air inlet heater will turn off when the sum of the coolant temperature and the inlet manifold air temperature exceeds 35 degrees Celsius or 127 degrees Fahrenheit.

Note: The boost pressure reading is used to determine atmospheric pressure. This will indicate if the engine is operating above 1678 m (5505 ft). If the altitude is above 1678 m (5505 ft), the temperature that activates the heater is adjusted in order to compensate for the extreme altitude. Refer to Illustration 4 for more details.

Active Open Circuit or Short Circuit Diagnostic Codes

The air inlet heater will turn on if the coolant temperature sensor has an active open circuit diagnostic code or an active short circuit diagnostic code and the inlet manifold air temperature is less than 10 °C (50 °F).

The air inlet heater will turn on if the air temperature sensor for the inlet manifold has an active open circuit diagnostic code or an active short circuit diagnostic code and the coolant temperature is less than 40 °C (104 °F).

Note: The coolant temperature and the inlet manifold temperature are measured in degree Celsius. The Caterpillar Electronic Technician (Cat ET) can display the coolant temperature and the inlet manifold temperature in degree Celsius or in degree Fahrenheit. The ECM adds the coolant temperature and the inlet manifold temperature together. Then, the ECM uses the sum of the coolant temperature and the air inlet temperature in order to determine if the air inlet heater should be on or off. Illustration 4 is a visual aid for troubleshooting the operation of the air inlet heater. The temperatures in degree Fahrenheit are not a direct conversion of the temperatures in degree Celsius.

The following procedure explains the temperatures that are shown in degree Fahrenheit:

• Convert the reading for the coolant temperature from degree Celsius to degree Fahrenheit.

• Convert the reading for the inlet manifold temperature from degree Celsius to degree Fahrenheit.

• Add the two conversions together in order to arrive at the correct conversion for the sum in degree Fahrenheit.

Illustration 1	g00856700
Typical diagram of components for the air inlet heater

Illustration 2	g00856847
Schematic of the air inlet heater

Illustration 3	g00726706
P2 ECM connector

Illustration 4	g00883284
Operational chart for the air inlet heater

Test Step 1. Inspect Electrical Connectors And Wiring

1. Thoroughly inspect the J501/P501 air inlet heater relay connector and inspect the J2/P2 ECM connector. Inspect the electrical connector J648/P648 for the lamp of the air inlet heater and inspect the terminal connections on the air inlet heater relay. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. 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 (terminal 8).

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and wiring for abrasion and for pinch points from the sensors back to the ECM.

Expected Result:

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

Results:

• OK - Proceed to Test Step 2.

• Not OK -

  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 2. Use the "Intake Air Heater Enable Test" to Check the Circuit

1. Turn the key switch to the ON position.

2. The lamp for the air inlet heater should illuminate for two seconds. The lamp for the air inlet heater should shut off.

3. Connect Cat ET to the data link connector.

4. Go to the "Intake Air Heater Enable Test" on Cat ET.

5. Start the test and listen for a click from the air inlet heater relay.

   Note: The air inlet heater relay is located on the front left side of the engine.

   Note: Do not leave the "Intake Air Heater Enable Test" on. Avoid unnecessary cycling of the air inlet heater in order to prevent the battery from discharging. The "Intake Air Heater Enable Test" has a one minute timer. When the one minute time expires, the test will stop.

Expected Result:

Result 1 The lamp illuminates and the relay activates.

Result 2 The lamp illuminates and the relay activates. The air inlet heater is still suspect.

Result 3 The lamp illuminates but the relay does not activate.

Result 4 The lamp does not illuminate.

Results:

• RESULT 1 - The lamp and the relay are functioning normally.STOP

• RESULT 2 - Proceed to Test Step 3.

• RESULT 3 - There is a problem with the relay circuit. Proceed to Test Step 4.

• RESULT 4 - Proceed to Test Step 5.

Test Step 3. Check the Voltage at the Relay Contacts for the Air Inlet Heater

1. Turn the key switch to the OFF position.

2. Disconnect the wire from the relay terminal of the air inlet heater to the air inlet heater.

3. Fabricate two jumper wires with Deutsch sockets on one end and Deutsch pins on the other end. Strip a small amount of insulation from the middle of one jumper wire.

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Illustration 5	g00726988
Connections for the Test Lamp

4. Disconnect J501/P501 and insert the jumper wires in the electrical connectors.

5. Connect a voltage test lamp from the disconnected relay terminal to the jumper wire that is connected to J501 and P501 terminals.

6. Turn the key switch to the ON position.

7. Go to the "Intake Air Heater Enable Test" on Cat ET.

8. Start the test and watch the voltage test lamp.

   Note: Do not leave the "Intake Air Heater Enable Test" on. Avoid unnecessary cycling of the air inlet heater in order to prevent the battery from discharging. The "Intake Air Heater Enable Test" has a one minute timer. When the one minute time expires, the test will stop.

Expected Result:

The test lamp turned on and the test lamp turned off with the "Intake Air Heater Enable Test".

Results:

• Yes -

  Repair: The air inlet heater relay and the +battery connection to the air inlet heater relay are OK. Leave the wire disconnected from the relay terminal.

  Proceed to Test Step 6.

• No -

  Repair: The test lamp does not come on or the test lamp remains on after the test lamp comes on.Reconnect the wire to the relay terminal.

  Proceed to Test Step 7.

Test Step 4. Check the Voltage at the Electrical Connector P501 for the Air Inlet Heater Relay

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Illustration 6	g00727002
Typical example of the locations for the components

1. Disconnect the J501/P501 connector for the air inlet heater relay.

2. Ensure that the J648/P648 connector for the air inlet heater's lamp is still connected.

3. Connect a voltage test lamp to the two terminals of the engine harness side P501 connector of the air inlet heater relay.

4. Turn the key switch to the ON position.

5. Go to the "Intake Air Heater Enable Test" on Cat ET.

6. Start the test and watch the voltage test lamp.

   Note: Do not leave the "Intake Air Heater Enable Test" on. Avoid unnecessary cycling of the air inlet heater in order to prevent the battery from discharging. The "Intake Air Heater Enable Test" has a one minute timer. When the one minute time expires, the test will stop.

Expected Result:

The test lamp turns on and the test lamp turns off with the "Intake Air Heater Enable Test".

Results:

• Yes -

  Repair: Replace the air inlet heater and rerun the test. Verify that the original problem has been resolved.

  STOP

• No -

  Repair: The connector P501 for the air inlet heater relay is not receiving the correct voltage.

  Proceed to Test Step 8.

Test Step 5. Check the Voltage at the Lamp for the Air Inlet Heater

1. Turn the key switch to the OFF position.

2. Locate the lamp in the dash for the air inlet heater. Remove the lamp from the dash.

3. Connect a voltage test lamp between the two terminals of the lamp socket.

4. Turn the key switch to the ON position.

5. Go to the "Intake Air Heater Enable Test" on Cat ET.

6. Start the test and watch the voltage test lamp.

   Note: Do not leave the "Intake Air Heater Enable Test" on. Avoid unnecessary cycling of the air inlet heater in order to prevent the battery from discharging. The "Intake Air Heater Enable Test" has a one minute timer. When the one minute time expires, the test will stop.

Expected Result:

The test lamp turns on and the test lamp turns off with the "Intake Air Heater Enable Test".

Results:

• Yes -

  Repair: Replace the lamp for the air inlet heater. Verify that the problem has been resolved.

  STOP

• No - Reinstall the lamp for the air inlet heater. Proceed to Test Step 9.

Test Step 6. Check the Wiring for the Air Inlet Heater

1. Turn the key switch to the OFF position.

2. Disconnect both wires from the air inlet heater.

3. Use a multimeter to measure the resistance between the two ends of the wire that connects the air inlet heater to the air inlet heater relay.

4. Measure the resistance from the engine ground stud to the other end of the wire for the air inlet heater that connects to the ground stud.

Expected Result:

The measured resistance is less than 20 Ohms.

Results:

• Yes -

  Repair: Replace the air inlet heater. Verify that the problem is resolved.

  STOP

• No -

  Repair: Repair the damaged wire. Verify that the problem is resolved.

  STOP

Test Step 7. Check the Relay Contact at the +Battery Terminal Connection

1. Turn the key switch to the OFF position.

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Illustration 7	g00727399
Connections for the Test Lamp

2. Connect a voltage test lamp from the terminal for the relay contact that connects to the circuit protection for the air inlet heater (wire K995-OR).

3. Connect the other end of the voltage test lamp to the engine ground stud.

4. Turn the key switch to the ON position.

Expected Result:

The test lamp comes on when the key switch is turned to the ON position.

Results:

• Yes -

  Repair: Repair the wiring between the lamp for the air inlet heater and the connector J648:B. Verify that the problem has been resolved.

  STOP

• No -

  Repair: Inspect the circuit protection for the air inlet heater and the air inlet heater wiring. Repair the wiring. Verify that the problem has been resolved.

  STOP

Test Step 8. Check the Battery Voltage to Connector J648 for the Lamp

1. Turn the key switch to the OFF position.

2. Disconnect the connector J648/P648 for the air inlet heater's lamp.

3. Connect a voltage test lamp to the terminal J648:A. Refer to Illustration 6.

4. Connect a jumper wire to the ground stud. Connect the other lead of the test lamp to the jumper wire.

5. Turn the key switch to the ON position.

Expected Result:

The voltage test lamp came on and the voltage test lamp stays on while the voltage test lamp is connected between J648:A and the ground stud.

Results:

• Yes - Proceed to Test Step 10.

• No -

  Repair: Repair the wiring. Verify that the problem has been resolved.

  STOP

Test Step 9. Check the Voltage at Connector J648/P648 for the Lamp

1. Turn the key switch to the OFF position.

2. Disconnect the connector J648/P648 for the air inlet heater's lamp.

3. Connect a voltage test lamp from the connector J648:A for the air inlet heater to the engine ground stud.

4. Turn the key switch to the ON position.

Expected Result:

The test lamp comes on and the test lamp stays on.

Results:

• Yes -

  Repair: Repair the wiring from the connector J648:B for the lamp. Verify that the problem has been resolved.

  STOP

• No -

  Repair: Repair the wiring from connector J648:A for the lamp. Verify that the problem has been resolved.

  STOP

Test Step 10. Check Battery Voltage to the Connector P501 for the Air Inlet Heater Relay

1. Turn the key switch to the OFF position.

2. Ensure that the connector J648/P648 for the air inlet heater's lamp is connected.

3. Disconnect the connector J501/P501 for the air inlet heater relay.

4. Connect a voltage test lamp from the connector P501:1 for the air inlet heater relay to the engine ground stud.

5. Turn the key switch to the ON position.

Expected Result:

The voltage test lamp comes on and the voltage test lamp stays on when the key switch is in the ON position.

Results:

• Yes - Proceed to Test Step 11.

• No -

  Repair: Repair the wiring from J648:A to P501:1. Verify that the problem is resolved.

  STOP

Test Step 11. Check the ECM

1. Turn the key switch to the OFF position.

2. Disconnect the connector J648/P648 for the air inlet heater's lamp.

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Illustration 8	g00727433
Connections for the Breakout T

3. Disconnect the J2/P2 ECM connector and install a 140-2266 Cable (Seventy-Pin Breakout) to the J2 ECM connector only.

4. Connect a voltage test lamp from the connector J648:A to the terminal 8 of the breakout T. Refer to Illustration 7.

5. Turn the key switch to the ON position.

6. Go to the "Intake Air Heater Enable Test" on Cat ET.

7. Start the test and watch the voltage test lamp.

   Note: Do not leave the "Intake Air Heater Enable Test" on. Avoid unnecessary cycling of the air inlet heater in order to prevent the battery from discharging. The "Intake Air Heater Enable Test" has a one minute timer. When the one minute time expires, the test will stop.

   Note: When the J2/P2 ECM connector is disconnected and the key switch is in the ON position, open circuit diagnostic codes will be active or logged for all of the engine sensors. This is normal.

Expected Result:

The test lamp turned on and the test lamp turned off with the "Intake Air Heater Enable Test".

Results:

• Yes -

  Repair: Repair the wiring from the connector P501 for the air inlet heater relay to the P2 ECM connector. Verify that the problem has been resolved.

  STOP

• No - Proceed to Test Step 12.

Test Step 12. Test the Battery Voltage to the ECM

1. Turn the key switch to the OFF position.

2. Disconnect the J1/P1 ECM connector and install a breakout T.

3. Connect a voltmeter between terminal 52 of the breakout T and terminal 65 of the breakout T. Refer to Illustration 8.

4. Turn the key switch to the ON position and check the voltmeter.

5. Turn the key switch to the OFF position.

6. Connect a voltmeter between terminal 53 of the breakout T and terminal 67 of the breakout T. Refer to Illustration 8.

7. Turn the key switch to the ON position and check the voltmeter.

Expected Result:

The voltage is between 11.0 VDC and 13.5 VDC when the key switch is in the ON position.

Results:

• Yes -

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

  STOP

• No -

  Repair: Inspect the vehicle wiring. Repair the vehicle wiring or send the vehicle to the OEM dealer for repair. Verify that the problem has been resolved.

  STOP