Fan Clutch behavior? - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 06-08-2019, 01:52 PM
airtight_python airtight_python is offline
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Fan Clutch behavior?

'05 TB. 4.2L. 90k. Have not had long but seems to be getting about 10.5 MPG currently.

I just replaced the fan clutch because I was getting MIL from the fan speed sensor.

Replaced with brand new Behr part number 376734021. MIL went away.

However, the clutch does not disengage on a cold motor. Now getting P0128. (Engine taking too long to heat up) It's stiff and will not continue to spin when kicked over but you can move it with your hand.

Is this the proper behavior of this new clutch or do I need to have the ebayer replace it?

TIA
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  #2  
Old 06-08-2019, 11:31 PM
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wcosh wcosh is offline
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Many people believe that only the GM AC Delco replacement fan clutch will work correctly with our vehicles. Some folks have even needed to go to dealer to have the computer re-flashed to make new fan clutches work correctly.
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Old 06-09-2019, 12:14 AM
airtight_python airtight_python is offline
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Thanks. The Behr clutch I installed is the updated OEM part. I'm asking if the clutch being stiff on a cold engine is normal behavior. I would assume not but I figured someone else with a working fan clutch could verify theirs is stiff or not on a cold motor.

Quote:
Originally Posted by wcosh View Post
Many people believe that only the GM AC Delco replacement fan clutch will work correctly with our vehicles. Some folks have even needed to go to dealer to have the computer re-flashed to make new fan clutches work correctly.
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  #4  
Old 06-09-2019, 11:06 AM
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wcosh wcosh is offline
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At startup my fan clutch will start engaged (roar) but will quickly release (a few seconds) and the noise settles down to a quiet idle.

Hope that answers your question.

hopefully your part settles in and starts to work as expected
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Old 06-09-2019, 02:19 PM
airtight_python airtight_python is offline
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Ok, kind of. I just put a couple hundred miles on it and I'm certain its still not right. It roars when you start it. It does quiet down just a bit. But even at highway speeds its still roaring. You can feel engine lag and the vibration of the fan in the steering and pedals. Pretty ridiculous that new manufacturing is such garbage.
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Old 06-09-2019, 07:54 PM
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OK . A P0128 would kill your fuel mileage and set that DTC with what your saying if the motor never fully warms up to about 205-210 degrees F on a scanner. Never read a gauge in the cluster as it can be inaccurate.

What happens >>> If the thermostat fails to close, the engine may never
achieve normal operating temperature. This will prevent it from going into closed loop feedback control of the fuel mixture
(which makes the engine run rich and waste fuel).

See it on the scanner to check feedback control open or closed.
A Bad thermostat is common issue.
Verify.

What code # was set to determine that the fan clutch was defective?
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Old 06-09-2019, 08:21 PM
airtight_python airtight_python is offline
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Yes, P0128 if I remember correctly was the engine taking too long to heat up. It does get to 200+ indicated by Car Scanner, it just takes 15-20 minutes of run time to get there. I figured this could be and probably is due to the fan running all out as it never threw P0128 prior to replacing the clutch. The old clutch wasn't locked up, intermittently, it would fail to engage when stopped.

I do have a replacement stat/housing here anyway. As well as both O2 sensors, and a set of plugs. OEM components. I'll get to them next weekend. 13MPG avg wont cut it.

P0526, I believe was what the clutch was throwing. It went away after installation of the new clutch.

I notice DOWNSTREAM O2 doesnt display a fuel trim but does display voltage within scanner. Is this normal?
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Old 06-10-2019, 08:33 AM
mddombrowski mddombrowski is offline
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Voltage is raw data and is used by the PCM to calculate STFT and LTFT. The B1S2 HO2S should show relatively constant voltage at constant throttle. B1S1 should swing back and forth. But now you're wandering from the original diagnosis and just throwing parts.

Start with a new thermostat and fresh coolant and leave the O2 sensors on your bench. If the engine does not reach proper operating temperature, the emissions control system defaults to open loop mode. It will increase the pulse width of the injectors. Fuel trim and the HO2S sensors do not come online until the vehicle switches to closed loop.
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Old 06-10-2019, 09:55 AM
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Thermostat needs a swap. Think how many cycles they do.

Now on the O2 Keep in mind its possible may not throw a code but yet be defective.
The O2 sensor reads unburned oxygen in the exhaust, and generates a voltage signal that is proportional to the amount of oxygen in the exhaust. The signal can vary from a low of about 0.1 volts up to a high of about 0.9 volts.
A low voltage signal indicates a lean fuel mixture. A high voltage signal indicates a rich fuel mixture. The engine computer uses the O2 sensor's
input to balance the fuel mixture during closed loop operation. A bad sensor may prevent the system from going into closed loop, and usually causes the fuel mixture to run rich causing an increase in fuel consumption and emissions.


You asked about fuel trim on the downstream but its only a tattler for the converter. * Note* A downstream oxygen sensor built in or behind the catalytic converter works exactly the same as an upstream O2 sensor in the exhaust manifold. The sensor produces a voltage that changes when the amount of unburned oxygen in the exhaust changes. However it only monitors the efficiency of the Cat itself.
The PCM monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. If the converter is doing its job and is reducing the pollutants in the exhaust, the downstream oxygen sensor should show little activity (few lean-to-rich transitions)).
The Downstream sensor's voltage reading should also be fairly steady (not changing up or down), and average 0.45 volts or higher.
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Old 06-10-2019, 10:32 AM
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Another thing i would look at.
Bad fuel mileage could be a faulty coolant temp sensor that always reads cold causing the fuel control system to run rich and waste fuel ?
Look up the specs and measure the resistance of it @ cold and @ operating temp.
If the resistance of a coolant sensor is within specs and changes as engine temperature changes, but the engine is not going into closed loop, the fault is in the wiring or PCM.
You can also check into the Voltage specs too.
A cold coolant sensor will read a few volts then as the engine warms up and reaches operating temperature it should gradually decrease its voltage.
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