Circuit Description
The electric cooling fan is controlled by the powertrain control module (PCM) through the cooling fan relay based on inputs from the following components:
| • | The engine coolant temperature (ECT) sensor |
| • | The intake air temperature (IAT) sensor |
| • | The A/C selector switch |
| • | The A/C refrigerant pressure sensor |
| • | The vehicle speed sensor (VSS) |
The PCM controls the cooling fan by grounding the cooling fan control circuit which turns ON the cooling fan relay.
The cooling fan relay will be commanded ON when the following conditions are met:
| • | The engine coolant temperature reaches 106°C (223°F) or more. |
| • | The A/C clutch is requested |
| • | The vehicle speed is less than 38 MPH. |
The cooling fan relay will be commanded ON regardless of the vehicle speed when the following conditions are met:
| • | A DTC is set that requests the coolant fan to be ON. |
| • | The engine coolant temperature is 151°C (304°F) or more. |
| • | The A/C refrigerant pressure is high. |
The cooling fan may be commanded ON when the engine is not running during a fan run-on condition described in the electric cooling fan general description portion of the service manual.
Conditions for Running the DTC
| • | The engine is running. |
| • | The battery voltage is more than 9.5 volts. |
Conditions for Setting the DTC
| • | The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match. |
| • | The condition must be present for a minimum of 6.25 seconds. |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) will illuminate the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM will record the operating conditions at the time during which the diagnostic fails. This information will store in the Freeze Frame and/or Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
| • | If the owner complained of an overheating problem, determine if the complaint was due to an actual boil-over, or if the Temp light or the temperature gauge indicated overheating. |
| • | Check for the proper amount of coolant in the system. |
| • | If the gauge or light indicates overheating but no boil-over is detected, the gauge or light circuit should be inspected. You can also check the gauge accuracy by comparing it to the engine coolant temperature sensor reading using a scan tool with the gauge reading. |
| • | If the engine is actually overheating, and the gauge indicates overheating but the cooling fan is not coming ON, the engine coolant temperature (ECT) sensor may have shifted out of calibration and should be checked. Refer to Temperature Versus Resistance . |
| • | If the engine is overheating, and the coolant fan is ON, the cooling system should be checked. Refer to the cooling and radiator section of the service manual. |
Test Description
The numbers below refers to the step numbers on the diagnostic table.
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Listen for an audible click when the fan control relay operates. Be sure that both the ON and the OFF states are commanded. Repeat the commands as necessary.
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This check can detect a partially-shorted coil which would cause an excessive current flow. Allow the coil to warm up by leaving the circuit energized for 2 minutes. When the fan control relay is warm, the coil may open, and the amps will drop to 0, or the coil may short, and the amps will be more than 0.75 amp.
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It is important to identify and test the fan control relay coil terminals in order to avoid an improper diagnosis.
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Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline™ information for PCM programming.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the On-Board Diagnostic (OBD) System Check? | -- | ||||||
Does the fan control relay turn ON and OFF with each command? | -- | |||||||
Does the current draw a measure less than the specified value shown but not 0? | 0.75 A | Go to Diagnostic Aids | ||||||
4 |
Does the DMM display infinite resistance? | -- | ||||||
Does the test lamp turn ON and OFF with each command? | -- | |||||||
6 |
Does the test lamp illuminate? | -- | ||||||
7 |
Does the relay operate? | -- | ||||||
8 |
Did you find and correct the problem? | -- | ||||||
9 |
Did you find and correct the problem? | -- | ||||||
10 |
Is the repair complete? | -- | -- | |||||
11 |
Is the repair complete? | -- | -- | |||||
12 | Replace the malfunctioning fan control relay. Refer to Air Conditioning (A/C) Compressor and Cooling Fan Relays Replacement . Is the action complete? | -- | -- | |||||
|
Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | -- | ||||||
14 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||
15 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
