Pesky P0128

[Charger17]

Hello all,
I am having a P0128 issue with my car, but the backstory. Last June/July (2016) I had a check engine light come on initially for my thermostat, I prolonged fixing that. And later turned out I had fallen victim to the Intake hose with a crack in the elbow, I prolonged fixing that as well and as a result or not, my catalytic converter that comes off the engine took a dump. I ordered a new hose, replaced the cat, and, got a new thermostat installed in September. The car ran fine and had no issues.
Recently though(Late November early December) my car started acting funny, the a/c didn't blow cold and my fan started kicking on in the engine bay. Eventually the CEL came on, I checked it and discovered I had 2 codes, both p0128(it's really annoying that an open t-stat throws a CEL). But when I cleared the code the car a/c blows cold again and the fan doesn't kick on. And it'll stay that way for a week or 2 and I'll notice the a/c is warm and sure enough I'll have a code to clear before the CEL comes on. I replaced the Coolant temp sensor, mainly because I didn't want to buy another 100$ T-stat for this thing right away, but that didn't fix it. Does anyone have any insight on this issue?

I have utilized this forum for a while without being a member and the information here is great!

Thanks all

 

[Papasonic]

I pretty much had the same issues with the wife's 1.8 LTZ sedan. The same code and light; same no AC compressor engagement; also no remote start.
What we didn't have is the fan coming on, but the wife complained of very little heat when the heater was on. I eventually replaced the thermostat assembly and coolant, and haven't had the problems reoccur. I know you replaced the thermostat, but do you get adequate heat. Just because the thermostat is new doesn't rule out a problem with it.
We also had the cracked air intake tube, but no code was associated with that. I repaired the intake tube as a temporary fix using CA glue, and numerous coats of Flex Seal. (As seen on TV) I have yet to replace the air tube as the temporary fix is holding up very well.
Back to the thermostat; my original was made of a composite/plastic material, and all components were molded in. The AC Delco replacement was a nicely machined alloy piece, with components held in with snap rings; quite different from the original part.

 

[Charger17]

Thanks for the response! My heat is actually fine it's been chilly where I am at so I've had to utilize it. To be fair I did skimp on my t-stay and got it from autozone as opposed to napa, I just wanted to re-verify.
I did fail to mention though that my scan tool measures engine coolant temperature, how accurately I don't know, and the average temperature I read after driving is roughly 150/170ish. It has plenty of coolant.
Just absolutely drives me insane that a thermostat is a check engine light. I've owned numerous GM vehicles and this makes me insane.

 

[rojoes]

Thanks for the response! My heat is actually fine it's been chilly where I am at so I've had to utilize it. To be fair I did skimp on my t-stay and got it from autozone as opposed to napa, I just wanted to re-verify.
I did fail to mention though that my scan tool measures engine coolant temperature, how accurately I don't know, and the average temperature I read after driving is roughly 150/170ish. It has plenty of coolant.
Just absolutely drives me insane that a thermostat is a check engine light. I've owned numerous GM vehicles and this makes me insane.

Does the check engine light go off after it has run for a while? If it does the heater circuit in the thermostat is the culprit. The Autozone thermostat carries a 1 year warranty....Maybe swap it out for another one since it's under warranty? Common part to fail I checked (via internet) and all Advance Autos and Autozones in my area are out of them. NAPA has many in stock but cost $35.00 more and carry a lifetime warranty vs 1 years for Advance and "The Zone"

 

[Charger17]

No unfortunately it doesn't, I have to clear it. It's more of a hassle for me to change the stat as I am stationed overseas and I have to order parts. So what would otherwise be a trip to the store and back turns into a month long ordeal to get the parts lol so before I load the money cannon and fire it at the car I'm trying everything I can to narrow it down

 

[rojoes]

No unfortunately it doesn't, I have to clear it. It's more of a hassle for me to change the stat as I am stationed overseas and I have to order parts. So what would otherwise be a trip to the store and back turns into a month long ordeal to get the parts lol so before I load the money cannon and fire it at the car I'm trying everything I can to narrow it down

Does the base you are on have an auto hobby shop?

 

[Papasonic]

I just wanted to re-verify.
I did fail to mention though that my scan tool measures engine coolant temperature, how accurately I don't know, and the average temperature I read after driving is roughly 150/170ish. It has plenty of coolant.

That coolant temperature is too low to satisfy the computer. I believe that the thermostat is supposed to open around 210 degrees. I know that when the thermostat is functioning properly; the heater and radiator hoses are too hot to hang onto comfortably with your hand.

 

[Charger17]

Does the base you are on have an auto bobby shop?

No, they have the locals do the work and they're garbage. I'm moving in less than a week to a base that actually has a lift.

That coolant temperature is too low to satisfy the computer. I believe that the thermostat is supposed to open around 210 degrees. I know that when the thermostat is functioning properly; the heater and radiator hoses are too hot to hang onto comfortably with your hand.

It would figure that the thermostat I just got and installed was defective.

 

[rojoes]

It would figure that the thermostat I just got and installed was defective.

Certainly sounds like that to me

 

[suitcasejefferson]

I know this is an old thread, but I was unable to get a response to my much more recent post about this same issue. My CEL comes on, I get code PO128, and my A/C works intermittently. I can disconnect the negative battery cable for a couple of minutes, and the CEL goes out, and the A/C comes back on. I replaced the thermostat a little over a year ago when I replaced the water pump. Both came from Autozone. I have the 1.4 turbo engine, not the 1.8. Is it likely to be the thermostat, or could it be the engine coolant temperature sensor or intake air temperature sensor? Is there any way to tell what it is? I hate to replace an expensive thermostat and still have the same problem, and I really don't want to take it to a shop and pay big bucks to get it diagnosed and pay for labor to replace parts I can replace myself.

 

[Tormach]

Might be the temp sensor in the water outlet on the driver's side of the block. I can't imagine your t-stat would go that quickly after replacement.

Could try checking the wire connectors as well, might be dirty or corroded or other.

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[suitcasejefferson]

I replaced the water outlet assembly almost 50,000 miles ago, when I found a crack in it. I'm assuming the temperature sensor is an integral part of the water outlet assembly, and replacing it means replacing the entire assembly. I have already checked the electrical connections on both the thermostat and water outlet assembly, and they seem to be fine. I've already ordered an AC Delco thermostat from Parts Geek, if that doesn't work I replace the water outlet assembly. Thank you for your response.

 

[Tormach]

I replaced the water outlet assembly almost 50,000 miles ago, when I found a crack in it. I'm assuming the temperature sensor is an integral part of the water outlet assembly, and replacing it means replacing the entire assembly. I have already checked the electrical connections on both the thermostat and water outlet assembly, and they seem to be fine. I've already ordered an AC Delco thermostat from Parts Geek, if that doesn't work I replace the water outlet assembly. Thank you for your response.

Nope the sensor in the water outlet can be removed. The new one you put in should of had a new one with it.

I will drop a pic of it's location.


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