p0171-bad thermostat - Chevy Colorado & GMC Canyon

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Old 10-30-2011, 11:05 PM   #1 (permalink)
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Default p0171-bad thermostat

I have a 2006 Chevy Colorado 2.8l with 55,000 miles and I have been getting the code p0171. In the past 6 months I have had the throttle body replaced, and an o2 sensor installed. While at the dealer they said that it needs a thermostat, because when accelerating the temp gage will drop to and will return to the mark after up to normal rpm. The dealer told me that the thermostat is not covered under my extended warranted. So I just wanted to know if the bad thermostat could make the code come up that it is running to lean. I have also cleaned the mass air sensor, and have checked the vent hose from the valve cover to the intake.
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Old 10-31-2011, 01:03 AM   #2 (permalink)
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p0171 is bank 1 lean. Thermostat has nothing to do with air /fuel . What intake do you have? Have you tweaked the crank case lines, maf, resonater box?
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Old 10-31-2011, 02:10 AM   #3 (permalink)
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Other than what has been done by my gm dealer I have done nothing other than maintenance to my truck. I was thinking that when the truck is cool that it my mix the fuel and air at a different ratio. I have cleaned my mass air sensor, checked the line from valve cover to intake. They changed my o2 sensor last week, and that’s when they told me about my thermostat was bad and needed changed. But I’m thinking that it may be my mass air sensor, and I’m not sure on how to check it.
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Old 11-02-2011, 09:57 PM   #4 (permalink)
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This is the reason of why I just joined this forum. I have a 2005 Chevy Colorado LS 3.5l WITH 146K. I came across this issue about 3 months ago. It only occurred on the highway when I would accelerate up a hill every now and then. Now about a week ago it happens once or twice even when I am just driving around town. I figured it was the thermostat but I am not sure. I haven't gone to the dealership yet because I really don't want to deal with them after my valve seat leak... Nothing but problems.

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Old 11-03-2011, 12:43 AM   #5 (permalink)
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Thermostats are cheap. They are between $14.00 and $40.00 from RockAuto. If you think that is your problem get one and replace it yourself.

I doubt it is running lean because of the thermostat, but the temp gauge fluctuating that much it sure indicates the thermostat is not closing completely
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Old 11-03-2011, 12:52 AM   #6 (permalink)
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If you do pull the thermostat, check for brownish orange residue on it and inside the radiator cap. If you see it, that is the Deathcool (Dexcool) antifreeze solidifying around it. Get that antifreeze out of there now.

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Old 11-15-2011, 04:14 PM   #7 (permalink)
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Quote:
Originally Posted by xkmacx86 View Post
p0171 is bank 1 lean. Thermostat has nothing to do with air /fuel . What intake do you have? Have you tweaked the crank case lines, maf, resonater box?
You are incorrect. While the thermostat doesn't send readings to the computer to change the A/F ratio, it will make the antifreeze too cold for normal operating temperature if its stuck open. The coolant temp sensor then reads reads that temperature and richens up the fuel mixture to warm up the engine and fluids.

Bluechevy: my experience with stuck thermostats on other vehicles is at highway speeds it will never reach normal operating temperature, especially in the winter. Does your truck hit normal temp when driving highway speeds when its cold (around or below freezing)?

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Old 11-15-2011, 05:08 PM   #8 (permalink)
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Matt Man is correct. The temperature sensor will change the fuel/air mixture. It's just like when it's a cold morning start, it runs rich. If you run a colder thermostat in the summer you will get the same result because your vehicle never reaches the temperature it's intended to reach.

A trick we used to do when I lived in a colder climate was to cover the lower 1/3 of the radiator with cardboard or something to keep air from passing by the radiator. If it is cold where you are at, you can try that too just to see if your gauge becomes more stable. Otherwise, it's probably time for a tstat!
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Old 11-15-2011, 08:01 PM   #9 (permalink)
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Quote:
Originally Posted by bluechevy206 View Post
While at the dealer they said that it needs a thermostat, because when accelerating the temp gage will drop to and will return to the mark after up to normal rpm.
I own a 2006 Colorado with a 2.8 and my temperature gauge has done the drop to 1/4 and back under acceleration since new. It has 27K on it now. When the truck was under warranty, I brought the temp gauge fluctuation issue up to the dealerships attention. They didn't seem too concerned about it.

I don't think it will fix your P0171.
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Old 11-15-2011, 10:43 PM   #10 (permalink)
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FrugalRado, I don't think it will fix the problem either. The engine running to cold should create a rich condition, not lean (as described above).

My understanding is that these trucks have two O2 sensors, the 2ndhw sensor may be bad as well? Not sure though. GM recommends having the fuel injection system seviced by a dealer regularly as well to help with idle issues and whatnot. I can't see paying for that regularly though.

-Matt
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