3114, 3116 and 3126 Engines Caterpillar

Probable Causes

• Extended heating cycle (any cycle)

• No heating cycles

• System check

Recommended Repairs

Extended Heating Cycle (Any Cycle)

Replace the control module for the air inlet heater (if equipped).

Note: Cycle times are approximate only. Some variance does not necessarily indicate a system failure.

No Heating Cycles

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Hot engine components can cause injury from burns. Before performing maintenance on the engine, allow the engine and the components to cool.

Check for the following problems:

• Faulty control module

• Faulty oil pressure switch

• Faulty coolant temperature sensor

• Faulty heater element

• Faulty power relay (magnetic switch)

System Check

Note: The step-by-step procedures that follow are diagnostic checks that must be performed in sequence. Failure to follow the sequence may result in an incorrect diagnosis and unnecessary expense.

• Lamp test

• Preheat cycle

• Crank heat cycle

• Regular heat cycle

• Heater element

• Coolant temperature sensor

• Oil pressure switch

Lamp Test

1. Inspect the lamp. Replace the lamp, if necessary.

2. Check the wiring harness for the lamp for damaged wires and for poor connections.

3. If the lamp does not illuminate after the lamp and the harness has been inspected, proceed with the tests that follow.

Note: If the coolant temperature is below 18.3° ± 2.7°C (65° ± 5°F), the system should go directly from the lamp test into the preheat cycle. The lamp will not turn off.

Preheat Cycle

Remove the cover from the controller in order to gain access to the power relay. With the help of an assistant, turn the ignition switch to the RUN position and feel the power relay (magnetic switch) for a click. The click indicates that the relay energized. If the power relay does not click, proceed with the following steps.

Note: Perform the following steps while the preheat cycle is active. The preheat cycle is active for thirty seconds. It may be necessary to reactivate the preheat cycle periodically while these diagnostic checks are performed. To reactivate the preheat cycle, turn the ignition switch to OFF and then turn the ignition switch back to RUN. The results will be incorrect if any of the steps are performed and the preheat cycle is inactive.

1. Disconnect the electrical connector at the control module. Attach a voltmeter between terminal "F" and terminal "A" of the vehicle side of the wiring harness.

2. With the ignition switch in the RUN position, the voltmeter should read 12 volts.

3. If the voltmeter does not read a voltage, inspect the vehicle wiring for a blown fuse, a damaged wire, or a poor connection. Check both the power wire (terminal "F") and the ground wire (terminal "A").

4. If the voltmeter reads 12 volts, reconnect the connector.

5. Disconnect the connector for the coolant temperature sensor from the wiring harness. Use a small jumper wire to connect the two terminals of the connector on the vehicle side of the wiring harness.

6. With the help of an assistant, turn the ignition switch to the RUN position and feel the power relay (magnetic switch) for a click that indicates that the relay energized.

7. If a click is felt, one of the following conditions exists:
   • The coolant temperature is above 29.4 °C (85 °F).

   • The coolant temperature sensor has not reset to the closed position because the coolant temperature is not below 18.3 °C (65 °F).

   • The coolant temperature sensor is faulty.

   Perform the "Coolant Temperature Sensor" test. Replace the coolant temperature sensor, if necessary.

8. If a click is not felt and the leads to the coolant temperature sensor are jumpered, connect a test light to the power relay. Power should be present at both terminals on the coil side of the relay.

   1. If power is present on the relay terminal that connects to the control module but not on the relay terminal that connects to the heater, replace the relay.

   2. If power is present on both sides of the relay, remove the ground lead from the relay. The ground wire attaches to terminal "D" of the control module. Ground the relay to the cylinder block. If the relay energizes, the control module is faulty. Replace the control module.

9. If the power relay (magnetic switch) energizes, but the heater does not operate, use a test light to check for power on the contact side of the relay. Lack of power indicates a wiring problem. Check the vehicle's harness for a damaged wire or a poor connection.

10. If power is present on the relay terminal that connects to the heater and the heater does not operate, inspect the ground wire to the heater. If there are no defects, perform the "Heater Element" test.

Crank Heat Cycle

If the air inlet heater does not work during the crank cycle, proceed with the following steps.

1. Follow Step 1 through Step 10 of the "Preheat Cycle" test. If the system operation is correct to this point, allow the heater to remain in preheat until the cycle ends. The cycle time is 30 seconds. Feel the power relay (magnetic switch) for a second click as the heater is deactivated. If the relay does not produce a second click, or if the relay remains on longer than 30 seconds, replace the control module.

2. The heater should be deactivated after the 30 second period. With the help of an assistant, turn the ignition switch from the RUN position to the START position and feel the power relay (magnetic switch) for a click. If the relay does not produce a click, proceed with following steps.

   1. Disconnect the electrical connector at the control module. Attach a voltmeter between terminal "B" and terminal "A" of the connector on the vehicle side of the wiring harness.

   2. With the ignition switch in the START position, the voltmeter should read 12 volts.

   3. If the voltmeter does not read a voltage, inspect the vehicle wiring for a blown fuse, a damaged wire, or a poor connection. Check both the power wire (terminal "B") and the ground wire (terminal "A").

   4. If the voltmeter reads 12 volts, replace the control module.

Note: The heater should continue to operate for a maximum of 60 seconds after the ignition is released from the START position if the engine is not operating. If the heater does not operate or if the heater operates for more than 60 seconds, replace the control module.

Regular Heat Cycle

If the heater does not work and the engine is running, proceed with the following steps.

1. Follow Step 1 through Step 10 of the "Preheat Cycle" test. For this sequence of steps, the engine must be running. If the system does not function and the coolant temperature sensor is jumpered, proceed with the following steps.

2. Leave the jumper installed for the coolant temperature sensor.

3. Disconnect the wiring harness connector at the oil pressure switch. Use a voltmeter to check for power at the connector on the vehicle side of the wiring harness.

4. If the voltmeter does not read a voltage, inspect the vehicle wiring for a blown fuse, a damaged wire, or a poor connection.

5. If the voltmeter reads 12 volts, disconnect the connector for the oil pressure switch from the wiring harness. Use a small wire to connect the two terminals of the connector on the vehicle side of the wiring harness.

6. With the help of an assistant, start the engine and feel for the click in the power relay (magnetic switch).

7. If the relay clicks, replace the oil pressure switch.

   Note: Check the oil pressure at the oil manifold before you replace the oil pressure switch. During engine operation, the oil pressure should be greater than 241 ± 69 kPa (35 ± 10 psi).

8. If both the coolant temperature sensor and the oil pressure switch are jumpered and the power relay (magnetic switch) does not click, the control module is faulty.

Heater Element

If the controller is operating properly but the heater remains inoperative, the heater element may be faulty. Use the following steps to check the heater.

Use an ohmmeter to measure the resistance across the two terminals of the heater. There should be very little resistance to the current flow.

1. If the ohmmeter reads an infinite resistance, the heater element is faulty. Replace the heater element.

2. if the ohmmeter reads a very low resistance, check the ground wire from the heater to the cylinder head.

Coolant Temperature Sensor

The coolant temperature sensor is designed to open at 29.4° ± 2.7°C (85° ± 5°F). The sensor is designed to reset at 18.3° ± 2.7°C (65° ± 5°F). To test the sensor, proceed with the following steps.

1. Remove the sensor from the water temperature regulator housing. Place the sensor in a container of cold water. The temperature of the water should be less than 10 °C (50 °F).

2. Connect an ohmmeter across the leads of the sensor. Allow the temperature of the sensor to equalize with the water temperature. Ensure that the temperature of the water remains near 10 °C (50 °F). The sensor should be closed at this point. The ohmmeter should read little resistance.

3. Place a thermometer in the container and heat the water slowly. Stir the water as the water is heating. The sensor should open at 29.4° ± 2.7°C (85° ± 5°F). The ohmmeter reading should change to infinite resistance.

4. Cool the water by slowly adding ice and stirring. When the water temperature drops to 18.3° ± 2.7°C (65° ± 5°F), the ohmmeter reading should change from infinite resistance to minimal resistance.

5. If any of these conditions are not met, the sensor should be replaced.

Oil Pressure Switch

The oil pressure switch is designed to open when the oil pressure falls below 241 ± 69 kPa (35 ± 10 psi). The switch should close above 241 ± 69 kPa (35 ± 10 psi). Use the following steps to test the oil pressure switch.

1. Turn the ignition switch to the OFF position. Disconnect the connector for the oil pressure switch in the oil manifold.

2. Connect an ohmmeter to the two terminals of the connector on the side of the wiring harness that goes to the controller.

3. The ohmmeter should read infinite resistance (open circuit).

4. Start the engine and increase the rpm until the oil pressure is 241 ± 69 kPa (35 ± 10 psi). As this time, the switch should close and the resistance should go from infinity to zero ohms.

5. Replace the oil pressure switch if the conditions in the previous two steps are not met.

Note: There is an optional 7E-9425 Temperature Switch for parts service. The 7E-9425 Temperature Switch will open at 48 °C (118 °F). This sensor will close at 35 °C (95 °F).

Note: There is an optional 4P-6602 Control Module for parts service. The optional control module has the same functions as the standard control module with the exception of different cycle times.