Code Analysis-P0128

[chascoll]

I had the codes pulled on my H3 yesterday after an engine light came on. Our Advance auto parts pulled the codes and found the P0128 and described it as "thermostat below operating temp." He said the possible causes could be bad sensor or too rich an anti-freeze mixture. I recently had the radiator replaced due to a crack in the plastic tank. They also replaced the thermostat. I removed some of the old red fluid left in the overflow tank and replaced it with new fluid. If the mixture is too rich, what is the best way to check? Your thoughts. 2006 model H3.

They also found a historical code (not sure what that means) of P0171. I read a post from 06 H3 talking about a similiar problem along with his troubleshooting. Our vehicle when purchased had a K&N kit installed and wonder if that had any impact on the MAF sensor. Anything else I should check, or do I need to worry about it?

Thanks for your help!

 

[ArtHummer]

I don't think that mixture can be to rich. The only problem that I faced with having it to reach is it actually corroding the aluminum(I found it really strange but 100% coolant started to erode aluminum). The mixture most like to lean and boils up to early. Also this code can be set by Air Intake Temperature Sensor.
You are saying that you have K&N filter and it allows more dirt in then oem filter. Both P0171 and P0128 can be set by improper air intake problems. I would definitely start with cleaning the air intake before changing anything.
Also... Why did the bottle cracked? Did you overheated the engine by any chance? Even if just a little bit, I would've relapse the coolant temperature sensor. It goes bad when overheated and you have to replace it with the thermostat.

 

[LagunaH1]

I'm by no means a mechanic but I have read several times that there is an ideal mix of antifreeze and water. Supposedly if you have too high a degree of antifreeze, the fluid won't conduct heat as well as a properly mixed fluid.

 

[chascoll]

Thanks for your reply

I don't think that mixture can be to rich. The only problem that I faced with having it to reach is it actually corroding the aluminum(I found it really strange but 100% coolant started to erode aluminum). The mixture most like to lean and boils up to early. Also this code can be set by Air Intake Temperature Sensor.
You are saying that you have K&N filter and it allows more dirt in then oem filter. Both P0171 and P0128 can be set by improper air intake problems. I would definitely start with cleaning the air intake before changing anything.
Also... Why did the bottle cracked? Did you overheated the engine by any chance? Even if just a little bit, I would've relapse the coolant temperature sensor. It goes bad when overheated and you have to replace it with the thermostat.

ArtHummer-I appreciate your input. To clarify, the plastic tank portion of the radiator assembly had cracked which prompted me to r/r the radiator. The overflow tank is good to go. I live on a clay dirt road, and I service the filter on a regular basis with the K and N recharge kit. Is the temp sensor avail at the parts store or do I have to go to GM? Also, is it an easy change for a diy?

Thanks!

 

[hummech]

hello chascoll, when that code is set it means that the thermostat is stuck open or it has too low of a temp. installed. when you start the vehicle and it is cold, the computer has a timer built into the program that looks how long the engine is running before it goes into closed loop for the computer to take over for emission reasons. if it takes too long then it will trigger P0128. i would change the therostat back to a factory one or if you already have one then it is defective and will need to be replaced. we get a lot of these codes in the winter time because people change their thermostats to cooler ones for summer driving.

 

[ArtHummer]

You can get the coolant temp sensor in some part stores and it is easy to change it. It's located on the back right side of the engine block close to firewall.

You can check the coolant mixture with some simple tools that you can get in any part sore. Best to have is 50/50. and it goes up to 70/30 for colder temperatures. I live in middle of east coast and always used 50/50 mix.

Also, K&N recharge kit is cleaning your filter to increase the air flow. But also it is oil based and excess of oil gets trapped in the Intake manifold and collects dust. I would clean the TB and MAF sensor first. Great write up in this post (http://www.hummer4x4offroad.com/for...body-and-MAF-sensor-cleaning&highlight=intake)

 

[Schwarttzy]

Sounds like you need to replace your thermostat, I had the same error code. You also need about 3 gallons of coolant once it drains. Now if you don't consider yourself handy, I wouldn't recommend doing it, because you have to remove the driver-side wheel well fender liner to be able to change it, and it isn't the easiest thing to do. Just for a bit more of perspective, I felt like I belong working at a dealership on cars after having zero problems and not breaking a single plastic clip when I installed mine.

 

[chascoll]

hello chascoll, when that code is set it means that the thermostat is stuck open or it has too low of a temp. installed. when you start the vehicle and it is cold, the computer has a timer built into the program that looks how long the engine is running before it goes into closed loop for the computer to take over for emission reasons. if it takes too long then it will trigger P0128. i would change the therostat back to a factory one or if you already have one then it is defective and will need to be replaced. we get a lot of these codes in the winter time because people change their thermostats to cooler ones for summer driving.

hummech- sounds good, however, I have no idea what type of thermostat the radiator shop put in. At the parts store, how do I specify when ordering part? Also, is there a post on how to change out the part (I have never worked on a gm before).

 

[chascoll]

reply

thank you again- I will test the mix before I mess with the thermostat. We are fixin to head to NY for the holidays and I want to make sure our hummer is ready for the weather. I also appreciate the MAF and TB link; I did stumble across it while reading some other posts.

This is a great forum!

 

[chascoll]

I hear ya man...I am not a mechanic by trade, but do enjoy the challenge and satisfaction that goes along with it.

 

[ArtHummer]

I found this how to by GM. Enjoy...

:link:

 

[chascoll]

Thanks ArtHummer!

 

[f5moab]

It goes bad when overheated and you have to replace it with the thermostat.

No true! It can go bad, but it does not need to be replaced if the engine overheats. It really depends on the reason for overheating.

 

[Firesquirt]

I had the same code replaced the thermostat (stuck open) no more code.

 

[poncho1965]

Same code here, installed a new thermostat, code cleared. My thermostat was not stuck open though....


Mike

 

[Michro]

Replaces my thermostat last week, code cleared. Seems to be common on IL5's