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Test Description

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  This step ensures that the DTC has failed this ignition cycle. If the scan tool displays Passed, then the answer is No.
  2. 3:  The cooling fan noise should increase as the cooling fan engages. It can take up to 2 minutes for full cooling fan engagement. If cooling fan 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.
  3. 4:  In the previous step the cooling fan was fully engaged. This step tests to ensure that the cooling fan will disengage. A noticeable noise difference should be heard between a fully engaged cooling fan and a disengaged cooling fan. The cooling fan is completely disengaged when the excessive fan noise is not heard.
  4. 5:  Tests the ability of the PCM to control the cooling fan speed. If answer to question is Yes, ensure to refer to all Diagnostic Aids.
  5. 6:  Disconnecting the cooling fan and running the engine ensure that the cooling fan is not engaged. When rotating the cooling fan it should spin freely. If not then the cooling fan will not disengage.
DTC P0495

Step Action Yes No
Schematic Reference: Engine Cooling Schematics 
Connector End View Reference:  Cooling System Connector End Views  
1 Did you perform the Engine Cooling Diagnostic System Check? Go to Step 2  Go to Diagnostic System Check - Engine Cooling 
2 
  1. With a scan tool, observe the Powertrain DTC list.
  2. Start the engine.
  3. Operate the vehicle within the Conditions for Running in the DTC.
Does the scan tool indicate the DTC Failed this ignition cycle?		 Go to Step 5  Go to Step 3 
3 
IMPORTANT: DTC P1482, for 4.2l (LL8), will set when the cooling fan relay is disconnected.
  1. Turn OFF the ignition.
  2. Disconnect the coolant fan relay.
  3. 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.
  4. Start the engine.
  5. Raise engine speed to 2000 RPM for 2 minutes.
Does the cooling fan engage?		 Go to Step 4  Go to Step 5 
4 
IMPORTANT: Continuously excessive fan noise is due to the PCM commanding the cooling fan to 100% engaged or a mechanical failure. If the fan noise decreases during this step, then this DTC is due to an electrical malfunction. Replacing the cooling fan will not correct the condition.
  1. Turn OFF the ignition.
  2. Remove the 10 amp fused jumper wire.
  3. Install cooling fan relay.
  4. Disconnect the cooling fan connector.
  5. Start the engine.
  6. Raise engine speed to 2000 RPM for 2 minutes.
Does the cooling fan disengage?		 Go to Step 5  Go to Step 11 
5 
  1. Install a scan tool.
  2. Start the engine.
  3. With a scan tool, observe the Fan Speed parameter in the PCM ENG 2 data list.
  4. Operate the engine at 2000 RPM for 2 minutes.
Is the cooling fan speed less than 1600 RPM?		 Go to Diagnostic Aids Go to Step 6 
6 
  1. Turn OFF the ignition.
  2. Disconnect the cooling fan connector.
  3. Start the engine.
  4. Run the engine at 2000 RPM for 2 minutes.
  5. Turn OFF the engine.
  6. Rotate the cooling fan 2 revolutions.
Does the cooling fan rotate freely?		 Go to Step 7  Go to Step 13 
7
  1. Disconnect the harness connector at the shroud.
  2. Turn ON the ignition.
  3. Connect a test lamp between the cooling fan clutch supply voltage circuit of the cooling fan and ground.
Does the test lamp illuminate?		 Go to Step 8  Go to Step 11 
8 Disconnect the cooling fan relay.
Does the test lamp remain illuminated?		 Go to Step 9  Go to Step 10 
9 Repair the cooling fan clutch supply voltage circuit of the cooling fan for a short to voltage. Refer to WIRING REPAIRS in Wiring Systems.
Did you complete the repair?		 Go to Step 14  -
10 Inspect for poor connections at the cooling fan relay. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS and CONNECTOR REPAIRS in Wiring Systems.
Did you find and correct the condition?		 Go to Step 14  Go to Step 12 
11 Inspect for poor connections at the cooling fan. Refer to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS and CONNECTOR REPAIRS in Wiring Systems.
Did you find and correct the condition?		 Go to Step 14  Go to Step 13 
12 Replace the cooling fan relay.
Did you complete the replacement?		 Go to Step 14  -
13 Replace the cooling fan. Refer to Fan Clutch Replacement .
Did you complete the replacement?		 Go to Step 14  -
14
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running in the DTC.
Does the DTC reset?		 Go to Step 2  System OK
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