P0495 code

[Dmflash]

Hey there , hoping for some advice. My trailblazer recently threw a p0495 engine code related to the fan clutch.
The truck starts with the normal high pitch fan sound but cuts out after a few seconds. It gets up to operating temp and doesn't over heat, also when the engine is off the fan spins as it should, not too freely but also not too hard to spin by hand.
Is it possible the relay is bad or a faulty sensor causing the code ? Thanks

 

[Mooseman]

I would suspect either the fan clutch or its wiring, which is notorious for rubbing through. Or the clutch is failing and running higher than it should.

 

[TJBaker57]

Hey there , hoping for some advice. My trailblazer recently threw a p0495 engine code related to the fan clutch.
The truck starts with the normal high pitch fan sound but cuts out after a few seconds. It gets up to operating temp and doesn't over heat, also when the engine is off the fan spins as it should, not too freely but also not too hard to spin by hand.
Is it possible the relay is bad or a faulty sensor causing the code ? Thanks

In over ten years of owning my own 2002 4.2 TrailBlazer I got this code once while travelling through Montana. I speculated that it may have been due to travelling at high speed into a stiff headwind. Sounds goofy but it is all I could come up with. I thought maybe the high speed air in through the radiator grille had spun up my fan??

At 65 mph my fan normally spins up at about 1100 to 1200 rpm without being commanded on by the PCM.

The code sets when in two consecutive ignition cycles the cooling fan exceeds 1600 rpm for more than 81 seconds while the fan is not commanded on, and the engine speed has been over 1800 rpm for more than two minutes.

I do not think the fan speed sensor could be the trouble.

 

[mrrsm]

Yes... The unlikely suspect of having a Shorted Wiring Harness is very possible when the Engine Vibrations have been rattling so much due to Bad Motor Mounts over the years and the Black PVC Wire Conduit vibrates back and forth long enough to work harden, rubbing through the insulation and Shorting Out the High Speed portion to Power at the little elbow shown below:



Likewise... another unlikely but possible suspect is having a Sketchy Fan Relay too, along with any Corroded Wiring or Pins in between in the Harness Connections at the Upper Driver's Side Radiator Fan Clutch Plug:


C

 

[TJBaker57]

It is worth mentioning here that shorted, broken, or otherwire compromised wires at the fan clutch cannot conceivably cause this particular code.

Such faults could cause a FAILURE of the fan clutch to operate, or a loss of the speed signal but neither of these would cause an overspeed condition.

Even a shorted 5 volt reference, which can cause a host of seemingly unrelated issues will not cause an overspeed of the cooling fan.

 

[mrrsm]

Another Good On Topic Thread:

How to test the electro-viscous fan clutch

So you suspect that your fan clutch is defective. One of two conditions is possible. If your fan is roaring like a jet engine after it has warmed up, DO NOT TEST. It's already confirmed that the clutch is locked up and needs to be replaced. Normally, it will roar a little on startup and...

gmtnation.com

 

[Mooseman]

It could be on the verge of locking up and is over speeding. Another possibility is that it's a cheap replacement and the sensor or internal speed controls are not working correctly.