Circuit/System Description
The control module sends a pulse width modulation (PWM) signal of 0-12 volts via the cooling fan clutch control circuit to the cooling fan relay. The control module monitors the cooling fan clutch control circuit during vehicle operation. When the cooling fan is commanded ON by the control module, the control circuit is at a low voltage. When the cooling fan is commanded OFF, the control circuit is near battery voltage. The control module uses this PWM to control the position of the oil control valve located inside the cooling fan clutch. If during operation, the control module detects an improper circuit condition on the cooling fan clutch control circuit DTC P0480 will set.
Description and Operation
Cooling Fan Description and Operation
The cooling fan relay sends a pulse width modulation (PWM) signal of 12-14 volts to the cooling fan clutch through the cooling fan clutch supply voltage circuit. The control module uses this PWM signal in order to control the speed of the cooling fan clutch. The signal controls the position of the oil control valve inside the cooling fan clutch. If the cooling fan RPM is different than the control module is expecting, DTC P0483 will set. The actual cooling fan RPM vs the desired cooling fan RPM is not always exactly the same. There can be up to an 800 RPM difference. If the control module detects that the cooling fan speed is over 6,800 RPM then DTC P0493 will set.
The cooling fan relay sends a pulse width modulation (PWM) signal (12-14 volts) to the cooling fan by the cooling fan clutch supply voltage circuit. The control module uses the PWM signal, which controls the speed of the cooling fan clutch by controlling the position of the oil control valve inside the clutch. If the cooling fan clutch RPM is to high when the control module is commanding 0 percent, DTC P0495 will set.
Cooling Fan Description and Operation
The control module uses the cooling fan speed signal in order to determine the actual fan speed in relation to the desired fan speed. The control module uses the cooling fan speed signal in order to reduce the cooling fan noise and in order to maintain the powertrain cooling requirements. The control module supplies power and ground to the clutch hall effect sensor of the cooling fan clutch. The hall effect sensor returns a signal pulse through the speed signal circuit in response to the reluctor track, which is located inside the fan clutch. If during operation, the control module detects a loss of the cooling fan speed signal, DTC P0526 will set.
Cooling Fan Description and Operation
The engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over-termperature condition. This condition occurs when the coolant temperature is above a calibrated value for a calibrated length of time. The ECM will disable half of the cylinders by turning OFF the fuel injectors. By disabling half of cylinders, the ECM is able to reduce the temperature of the coolant.
- «Cooling System Description and Operation»(ref-277788-S36694479812008011800000)
- «Instrument Cluster Description and Operation»(ref-277729-S16685249062008011800000)
- «Indicator/Warning Message Description and Operation»(ref-277729-S08345927332008011800000)
- «Audible Warnings Description and Operation»(ref-277729-S24731617042008011800000)
The control module sends a pulse width modulation (PWM) signal of 0-12 volts via the cooling fan clutch control circuit to the cooling fan relay. The control module monitors the cooling fan clutch control circuit during vehicle operation. When the cooling fan is commanded ON by the control module, the control circuit is at a low voltage. When the cooling fan is commanded OFF, the control circuit is near battery voltage. The control module uses this PWM to control the position of the oil control valve located inside the cooling fan clutch. If during operation the control module detects an improper circuit condition on the cooling fan clutch control circuit, DTC P1482 will set.
The optional coolant heater operates using 110 volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather. There is an internal thermal switch in the power cord that prevents operation above -18°C (0°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the plug when not in use.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 2: There should be no binding or increased resistance as the cooling fan clutch is rotated.
- 4: The cooling fan noise should increase as the cooling fan clutch engages. It can take up to 2 minutes for full cooling fan clutch engagement. If cooling fan clutch is previously fully engaged, then there will not be a noticeable change in cooling fan noise. Compare noise to a known good vehicle. If fan noise is louder than the known good vehicle, then answer Yes.
- 5: In the previous step the cooling fan clutch was fully engaged. This step tests to ensure that the cooling fan clutch will disengage. A noticeable noise difference should be heard between a fully engaged cooling fan clutch and a disengaged cooling fan. The cooling fan clutch is completely disengaged when the excessive fan noise is not heard.
- 7: This step clears DTCs that were set during previous steps. Test driving the vehicle will attempt to set DTCs not previous found in the Engine Cooling Diagnostic Check. If no DTC is set, the condition is a normal operation of the cooling fan.
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views DEFINITION: The cooling fan clutch has excessive fan noise. | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 2 | Rotate the cooling fan 3 complete revolutions? Is the resistance of the cooling fan clutch even throughout each rotation? | Go to Step 4 | Go to Step 3 |
| 3 | Inspect the cooling fan clutch for proper installation. Refer to Fan Clutch Replacement . Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
| 4 | IMPORTANT: DTC P1482 for 4.2L (LL8) and P0480 for 5.3L (LM4) will set when the cooling fan relay is disconnected. Turn OFF the ignition. Disconnect the coolant fan relay. Connect a 10-amp fused jumper wire between the cooling fan clutch supply voltage circuit of the cooling fan and the ignition 3 voltage circuit of the cooling fan relay. Start the engine. Raise engine speed to 2,000 RPM for 2 minutes. Does the cooling fan clutch engage? | Go to Step 5 | Go to Step 8 |
| 5 | IMPORTANT: Continuous excessive fan noise is due to a mechanical failure. If the fan noise decreases during this step, then there is an electrical malfunction. Replacing the cooling fan clutch will not correct the condition. Turn OFF the ignition. Remove the 10-amp fused jumper wire. Install the cooling fan relay. Disconnect the cooling fan clutch connector. Start the engine. Raise the engine speed to 2,000 RPM for 2 minutes. Does the cooling fan disengage? | System OK | Go to Step 6 |
| 6 | Turn OFF the ignition. If the A/C system was operating, then wait for approximately 2 minutes. Install J 43600 ACR 2000 Air Conditioning Service Center. Turn ON the ignition, with the engine OFF. With a scan tool, observe the A/C High Side Pressure Sensor parameter. Compare the A/C high side pressure on the scan tool to the high side pressure on J 43600 . Are the high side pressure values within 138 kPa (20 psi) of each other? | Go to Step 7 | Go to Step 9 |
| 7 | Turn OFF the ignition. Connect the cooling fan clutch connector. Turn ON the ignition, with the engine OFF. With a scan tool, clear all DTCs. Start the engine. Test drive the vehicle. With a scan tool, observe the DTC list. Does the scan tool display any cooling system DTCs? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK |
| 8 | Inspect for poor connections at the harness connector of the cooling fan clutch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
| 9 | Inspect for poor connections at the harness connector of the A/C high side pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 12 | Go to Step 10 |
| 10 | Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement . Did you complete the replacement? | Go to Step 13 | |
| 11 | Replace the cooling fan clutch. Refer to Fan Clutch Replacement . Did you complete the replacement? | Go to Step 13 | |
| 12 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 8 |
| 13 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3 |
| IMPORTANT |
|---|
| DTC P1482 for 4.2L (LL8) and P0480 for 5.3L (LM4) will set when the cooling fan relay is disconnected. |
| IMPORTANT |
|---|
| Continuous excessive fan noise is due to a mechanical failure. If the fan noise decreases during this step, then there is an electrical malfunction. Replacing the cooling fan clutch will not correct the condition. |
Excessive Fan Noise