P0128 engine code - 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 10-05-2008, 12:43 AM
CFD911 CFD911 is offline
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2004 Chevy TrailBlazer LT
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P0128 engine code

Hello Everyone

Well I just bought a 2004 TB 4x4.

So needless to say i am new to this site.

Not long after i got the truck the engine light cameon. I putthe OBD II reader on it and came up PO 128. I did my research and read the forums on this site to others having the same problem and it being the thermostate. (problems being engine light, a few degrees under proper operating temp. when the light came during driving etc.)

The only thing that is bugging me is
1. I added engin coolant to the holding tank not alot, the level was just under the full when cold line. and the light wnt off for a few trips on its own.

2. It takes 2-3 cold starts before the light comes on again after clearing it with the reader.

3. The light went off tonight on my way home long after engine at operating temp. with the guage still a few notches under the 100 degreese C mark.

I don't like fixing things that don't need fixed, and between me and my dad we are pretty handy around vehicles and knowing all this info, we believe it is the thermostat but not sure... Anyone have any suggestions???

thanks

Craig
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  #2  
Old 10-05-2008, 12:58 AM
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brendanpower brendanpower is offline
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Thermostat is probably sticking open a bit. I would suggest replacing it before winter, or it will be a long cold one waiting for your truck to warm up.
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  #3  
Old 10-05-2008, 11:25 PM
WOOLUF1952 WOOLUF1952 is offline
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  #4  
Old 10-06-2008, 05:56 AM
CFD911 CFD911 is offline
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Thanks.

The light is currently off. So i think i will replace it when the light comes back on.
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  #5  
Old 10-06-2008, 08:46 AM
Abelcastro1 Abelcastro1 is offline
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Hi and welcome to the site I had the same problem last month, same PO128 code, engine light would come on and off every other day. What I did is took the plunge and bought the thermostat, replaced it myself and voila problem solved. I also think my mpg's went up by two or so, I hear that if the engine is not running at the programmed temperature the pcm is dumping more fuel trying to warm it up, but it won't warm up enough if the thermostat is stuck open.
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Old 10-06-2008, 09:12 AM
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Blazernut Blazernut is offline
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Quote:
Originally Posted by Abelcastro1 View Post
Hi and welcome to the site I had the same problem last month, same PO128 code, engine light would come on and off every other day. What I did is took the plunge and bought the thermostat, replaced it myself and voila problem solved. I also think my mpg's went up by two or so, I hear that if the engine is not running at the programmed temperature the pcm is dumping more fuel trying to warm it up, but it won't warm up enough if the thermostat is stuck open.
This is right on the money. My engine was running cooler because of the thermostat my MPG went in the tank. The longer you leave it the more it will cost you in fuel. I got my thermostat from LORDCO ..... make sure it comes with the thin rounded rubber "O" ring in place in the groove on the outside edge.

I think back to when it first started to go out and I must have wasted at least a hundred dollars in fuel.
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  #7  
Old 10-06-2008, 02:49 PM
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rbarrios rbarrios is offline
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sure does sound like the thermostat is getting lazy.

but if you have not seen this thread....
heres a how to I made when I replaced mine....



http://forums.trailvoy.com/showthrea...t=32326&page=6
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Old 10-06-2008, 04:20 PM
CFD911 CFD911 is offline
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Wow the MPG will really will really be affected by only a couple degrees different in the engin.
And yeh i did see thatlink about how the thermostate was changed, i think i saw another one on here as well. As for repairs on cars it seems like a relitivly easy fix. I think i will replace it as soon as i get my Hanes repair manual in the mail this week.

Thanks Guys
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  #9  
Old 10-06-2008, 05:34 PM
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Stoli Stoli is offline
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I had the CEL come on a couple of weeks ago. The light went out after a couple of days. I checked to see if there was still a code in memory and there was, PO128. I haven't had the light come back on and I have tried making it come on by cruising down the highway on a cold night with the heat going and nothing happened, temp is right around 210. Does this mean that I don't have a problem and it was just a momentary hiccup or is there a mentality that once you have the light, you always have it until you replace the part? Thanks for the help.
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Old 10-06-2008, 06:40 PM
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One of the criteria for that P0128 light to come on is that the computer looks at the engine temp when it is 1st turned on from being cold.
It expects the engine temp to reach a certain temp in a certain amount of time. (i dont know the temp and time)... but if it sees that it doesnt reach this temp - in several cold start attemps- then it sets the light....


so maybe next time you start the car- you may want to set the heater to blow on high as soon as you turn on car... maybe this will 'rob' enough heat from the cold engine that it will set the light.... worth a try.
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