Question about 2003 GMC Envoy

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My Envoy has a trouble code P0495. Technician's

My Envoy has a trouble code P0495. Technician's preliminary analysis is a failed cooling fan clutch. Car is not overheating. Does the clutch typically fail in the locked position and manifest itself with a loud racing sound? Is there a relay that engages the fan clutch? If so, how do I perform the necessary fault analysis to isolate the specific problem?

Thank you!

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Test

Posted on Jan 16, 2010

  • pa1adin
    pa1adin Jan 16, 2010

    sorry for the 'test' post. I realize this question is old, but many people will search for it, so I am answering...

    your problem is definitely the fan clutch. replace it asap or it will tear up the front bearing in your water pump, followed by your belt and plastic shroud housing. It's expensive but necessary. It is the big grey-metal looking thing with heat fins that the plastic radiator fan is bolted to. It can not be fixed [afaik] and must be replaced. It can go bad even after only 3-5 years. If your notor sounds like a jet taking off all the time, this is the bad boy. replace asap!


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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), and P0480, for 5.3L (LM4), will set when the cooling fan relay is disconnected.
  1. Turn OFF the ignition.
  2. Disconnect the cooling fan relay.
  3. Connect a 10 amp fused jumper wire between the cooling fan clutch supply voltage circuit of the cooling fan clutch 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 clutch engage?
Go to Step 4
Go to Step 5
4
Important: Continuously excessive fan noise is due to the PCM commanding the cooling fan clutch 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 clutch 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 clutch connector.
  5. Start the engine.
  6. Raise engine speed to 2000 RPM for 2 minutes.
Does the cooling fan clutch 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 Fan Speed parameter less than 1600 RPM?
Go to Diagnostic Aids
Go to Step 6
6
  1. Turn OFF the ignition.
  2. Disconnect the cooling fan clutch 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 clutch 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 clutch 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 to 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 clutch. Refer to Testing for Intermittent Conditions and Poor Connections and to 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 clutch. 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

Posted on Jun 27, 2009

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I have a 2003 trailblazer with a code P0495. Making a loud
fan noise, but not over heating

Posted on Nov 29, 2009

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