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2005 GMC Envoy 4.2 4x4 P0128
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MarineGrunt
Enthusiast
Dec 8, 2012, 12:38 PM
Post #1 of 12
(9780 views)
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2005 GMC Envoy 4.2 4x4 P0128
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Check engine light came on the other day so I just got the code read. The code P0128 came up. It said something about the coolant temperature below what it should be. I replaced the thermostat back in May after we bought the Envoy. I know that doesn't mean anything. Everything seems to be working fine. Temperature gauge is where it normally is. Heater blows hot. If it wasn't for the check engine light you wouldn't think anything is wrong. I'm going to be out and about getting a Christmas tree so hoping to pick up any parts or whatever else is needed since my local parts store closes at 2:00 and closed in Sundays. Any ideas of what it could be and how to check for the problem?
Thanks!
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Sidom
Veteran
/ Moderator
Dec 8, 2012, 1:00 PM
Post #2 of 12
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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If you had a high end scanner you could check the freeze frame data and see when the failure happened & what the temp was. Also you could check the datastream and see what the coolant temp is....
If you don't have access to that, the easiest & cheapest route would be to install an OE tstat, clear the code and see what happens...
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 8, 2012, 1:11 PM
Post #3 of 12
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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That's usually just a bad thermostat, just not getting hot enough.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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MarineGrunt
Enthusiast
Dec 8, 2012, 1:29 PM
Post #4 of 12
(9735 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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I have to wait until Christmas morning for the high end scanner that HT is getting me.  I've heard that he's even going to fly up and teach me how to use it.
What do you think of those cheap $100 scanners just so I could pull basic codes and clear them? I think I've even seen the very basic ones on sale for $50. Would one of those work just to read and clear codes? It would be nice to not have to run to the parts store every time I need a code read or cleared. Not that it happens very often, but if a $50-$100 one would work for that, why not.
Thanks guys. I'll get a new thermostat from the dealership on Monday and go from there.
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Discretesignals
Ultimate Carjunky
/ Moderator
Dec 8, 2012, 1:31 PM
Post #5 of 12
(9734 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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GM made them really easy to change. You'll like that one.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 8, 2012, 1:53 PM
Post #6 of 12
(9722 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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MG, I have one of those pocket scanners that I use all the time for a quick read or code clear. Mine is a Mac that I paid about $200 for but it has data and stuff too. It's the hard stuff and the systems other than OBD2 generic that you need something better for. There are all kinds of lighting, restraint, suspension, ABS, instrument cluster, BCM and even alignment modules now that those things will be no help.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
Veteran
/ Moderator
Dec 8, 2012, 2:06 PM
Post #7 of 12
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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I have a cheap OTC as well.....The amount of data you can get with some of these cheap ones is pretty good. Some have a datastream and that is all you need some of the times...
I'm like you, I'll grab the OTC 1st, mainly because as soon as I plug it into the DLC, its on, my modis take a few minutes to boot & another couple of minutes for the VIN entry. So as long as it's something easy then the OTC is great. If I get an undefined code, need FF or the scope then I have to go the other route...
I honestly don't keep up on the cheap stuff. I'm only aware the additions is when a tech gets one. The last one I was surprise to see that it had OBD I abilities.....Hell I guess bi-direction controls is the next thing...........lmao
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MarineGrunt
Enthusiast
Dec 9, 2012, 12:35 AM
Post #8 of 12
(9690 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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I'll have to do some research on them I guess. I've kind of browsed online but have never really compared any. Unless you can recommend one that you think would be good enough for me. What model of Mac do you have HT? To be honest, right now, just one that reads and clears codes is all I really need. But, if I'm going to spend the money, it would be nice to have other options to tinker around with in the future. I don't really want to spend more than around $200-$300 or so but it seems there are plenty out there for less that will do more than I'll ever really need.
Hey DS. We're you being sarcastic about the thermostat? I put one in the Envoy back in May, and although it wasn't too bad, it wasn't as easy as my old cavalier work car I use to have! If I remember right I had to pull the alternator to get to it on the Envoy. Well, I'm not sure that I had to but did to make it easier to get to one bolt that was a pain.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 9, 2012, 6:51 AM
Post #9 of 12
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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I have this one, made by Launch but re-branded for Mac but I'm not saying this is the best way to go. It works for me. It boots up fast and I like the color screen. I think the Mac price is down to $169 now
http://www.launchtechusa.com/assets/products/CreaderVI.pdf
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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MarineGrunt
Enthusiast
Dec 16, 2012, 9:55 AM
Post #10 of 12
(9630 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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I'm sure this is just coincidence but thought I would ask. The other day I ran to the store and the check engine light was still on from when it threw the P0128. After leaving the grocery store I went to the gas station to get gas, light still on. After pumping gas I started it up and the check engine light was no longer on. I know the cooling system is separate from the fuel system but didn't know if maybe the gas cap not being tight enough had anything to do with the code. With all of the sensors on cars nowadays I didn't know if it could affect something else. Probably a stupid idea but it just seemed odd how the check engine light went off when it did after being on for a week.
Since it's off, and I did replace the thermostat in May, do I need to mess with it or should I wait until it comes on again? The Envoy didn't show any signs of trouble even when the check engine light was on. I do need to drain some of the antifreeze and strengthen the potency as it only tested for 5 degrees and it gets colder than that here in the winter. It was down in the 20's the other day when it threw the code so didn't know if the potency and outside temperature could cause it to throw the code? Probably another stupid idea, but hey, I come here so you guys can smarten me up. Since I've been a member of this forum I've learned more about vehicles in the past year than I have in the past 10 years. I know you guys just love answering my stupid questions.
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Sidom
Veteran
/ Moderator
Dec 16, 2012, 10:18 AM
Post #11 of 12
(9628 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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With a lot of failure that turn on the SES. The comp is still monitering that circuit. After it runs the same test and it passes so many times in a row the comp will turn off the light and story the code in history.
If I had to guess I would say that Tstat stuck open just enough to lower the coolant temp & set the code and is now operating properly......Unless you live in a very cold area and had a cold snap. In very cold areas a fully exposed radiator can get the coolant pretty cool before it goes back into the motor and might set that code..... That is why you see trucks with covers on their radiators just barely unzipped when it's real cold, it doesn't need the full area to run at proper temps...
Personally if I even suspected my Tstat was sticking......either way open or closed, I would be tempted to change it out.....Sticking stats can be bad news at the worst possible time....
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MarineGrunt
Enthusiast
Dec 16, 2012, 10:50 AM
Post #12 of 12
(9623 views)
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Re: 2005 GMC Envoy 4.2 4x4 P0128
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Thanks for the explanation Sidom. I live in Central IL and it did cool off for a few days this past week but we're back in the upper 40's now. I'll go ahead and change it out just to be safe. I planned on doing it this past Monday but then noticed the head gasket leak on the wife's old Venture so started that instead. I should finish the Venture up today and will then tackle the t-stat in the Envoy. After that I think the only thing I'll have to do is the rear main seal in the Sierra. Ha, it never ends! Oh well, with work being as slow as it is for me it gives me something to do plus, I enjoy it. I don't know though, if this Venture doesn't turn out I think I might "float test" all of my tools and be done with it all!
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