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2003 chevy trailblazer_lt_ext
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Discussion Starter #1
Hello, it has been a while since I have been on here but I need help from the community. I see many threads on faulty clutch fans but I cannot find one that fits my problem. I have had my TB since new in 03 (225k miles) and this is my 3rd fan clutch. All repairs on vehicle to date done by me (okay my brother helps ;) Symptoms = Clutch locked on at engine start and releases after about 1/4 mile. After much stop and go, engine will begin to run hot but has not overheated yet. Sometimes fan clutch will engage at a light and I can see temp dropping. Sometimes it won't and AC starts to malfunction while temperature goes over 210. Current fan clutch is new after market from Amazon but did not solve the problem. Replaced engine coolant temp sensor in case that was sending bad info. That did not fix the problem. I have a good digital multi-meter but without specific testing instructions, I am not great at troubleshooting. I don't think it is the fan clutch since the old one and new one were doing the same thing (barring a bad part). It seems the fan is either fully engaged or not at all but is NOT locked all the time. Could there be an AC sensor giving bad information? Any help with troubleshooting is appreciated.
 

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2004 chevy trailblazer_lt
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129 Posts
Have you ever replaced the thermostat or water pump? Is your cooling system full? Have you scanned for OBDII codes?
 

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2003 chevy trailblazer_lt_ext
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Discussion Starter #3
Have you ever replaced the thermostat or water pump? Is your cooling system full? Have you scanned for OBDII codes?
Entire cooling system replaced about a year ago (Radiator, water pump & thermostat). Coolant levels fine. Only use Dexcool in system. AC system replaced about 1.5 years ago. All were operating normally until all the sudden the fan clutch started locking at start-up and releasing within a few minutes after driving on a stretch and hitting higher RPM's. I replaced the Fan Clutch with an aftermarket part but it was immediately doing the same thing. I replaced the coolant temperature sensor. The clutch will occasionally engage when sitting at a light but it "sounds" to me like it is always either fully engaged or free spinning. I need help with troubleshooting the circuit. I have a good meter but need help with someone who knows how to test the circuit. I feel like it could be an AC sensor or PCM causing the issue but until I know how to test the circuit I cannot be sure.
 

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2004 chevy trailblazer_lt
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129 Posts
OK, but have you scanned for any OBDII codes, and what are they if there are any?
 

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2003 chevy trailblazer_lt_ext
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Discussion Starter #5
No codes. Check engine light is not on. I do have a code reader and I have scanned to check...
 

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2004 chevy trailblazer_lt
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129 Posts
Thank you for the code information.

Do you have a copy of the factory service manual, a Haynes book or a subscription to Alldatadiy? You will really need one of those in order to get a schematic for the fan clutch circuit. If you don't, I would recommend you get a Haynes manual as it will have at least a basic electrical diagram for that should include the cooling fan system.

Regarding your aftermarket fan clutch, did you get a Hayden or Four Seasons fan clutch? I ask because I know that in the original fan clutches that came from the factory, there was a problem with the oil used in the viscous clutch. Apparently, the oil degraded the polymeric parts in the clutch and the clutch would fail. I know when I replaced mine three years ago, I purchased a NAPA branded Hayden manufactured fan clutch. The only other brands besides ACDelco and Hayden I would purchase are Four Seasons (a sister company of Hayden) or Behr/Hella. Any of the others would be a crap shoot in my opinion.

In the mean time, if your code reader/scanner can read live data, I would monitor the engine temperature on it and compare it to what the instrument panel temperature gauge says the temperature is. You might also want to unplug the connector from the intake air temperature sensor and make sure that there is no corrosion and that the contacts are clean and then plug the connector back in.

I seem to recall reading somewhere that in some years/models of TrailBlazers, the PCM needs to be updated if the fan clutch is replaced. If you know someone in the service department at a Chevy/GMC dealership, you might want to ask them. I had my 2004 TrailBlazer in for some driveline and ABS problems, and I inquired about the fan clutch update for my '04 and was told that it did not apply to my '04.

I just ran across this on the rockauto website. It's the information page for the Hayden fan clutch for your 2003 TrailBlazer - "The ECM/PCM signal controls the level of engagement of the EV clutch. An internal solenoid opens a spring loaded valve which allows silicone drive fluid to flow from the storage reservoir to the working area of the unit engaging the clutch. This engagement process is ultimately controlled through the ECM/PCM by the following input variables: Coolant Temperature, Intake Manifold Temperature, Transmission Oil Temperature, A/C Pressure and Engine Oil Temperature." Here is the link to the page More Information for HAYDEN 3200. All the more reason to get a Haynes manual, factory service manual or a subscription to Alldatadiy,com. A complex sequence of events.

Good Luck!
 

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2003 chevy trailblazer_lt_ext
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Discussion Starter #7
Thanks for the info. The fan clutch I put in is an off-brand but is the same one I used several years ago. The symptoms never changed after the replacement so I am assuming the old one was not the cause of the problems. I think I found a proper circuit diagram so I will start testing the sensors that feed information to the PCM. I am betting one of them is faulty. I will also check with the dealer about the PCM update.
 

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2003 gmc envoy_sle
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54 Posts
Don't discount that the thermostat could have been sticking, even if it was new. Packing, shipping, being dropped maybe, can cause a bind in it's operation. Again, brand can matter here too.
 

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2005 buick rainier
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DIY work is going to be tough on modern vehicles if you don't have the proper tools and resources. I can explain the operation and what a shops diagnostic routine will encompass. Operation : PCM controls the fan clutch relay via a Pulse Width Modulated signal. The relay controls an oil control valve in the fan clutch to increase / decrease viscous clutch engagement - On time increases fan speed, off time decreases fan speed. The PCM uses more that the coolant sensor, it uses VSS, AC pressure, trans temp & ambient temp sensors. The PCM can monitor fan speed via a hall effect sensor in the fan clutch assembly. So what does a shop do when a fan clutch issue is suspected. Start with a visual inspection of the fan clutch, relay & wiring. Use a professional grade scanner to check for codes (follow diagnostic routine if present). No codes take a look @ all sensor related PID data to see if anything is out of range. Most professional scan tools will also allow for bidirectional operation of the fan itself. Put all this together w/ a wiring diagram and its destined to be fixed in a timely manner.

So what does the DIY guy do w/o a fancy scan tool? I would suggest obtaining a one time use Mitchell wiring diagram. Once you have the diagram you can prove out the circuits, You can rudementally check for basic powers and grounds. If your DVOM has "duty cycle" it may help w/ fan on / off time control.
 

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Did the new clutch come with a new wiring harness? The harness can cause all these issues. I spliced mine back together when it rubbed itself apart and cause open AND shorted circuits.
 
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