yet another p0128 thread but hopefully with more troubleshooting

[kickass audio]

Okay guys, now before we get started I know this has been discussed several different areas on here but no real diagnostic steps were noted so thats why I wanted to start this in hopes of pinning down what can be bad.

On that note... I have an 04 GMC Envoy, 4.2l I6 that threw a p0128 code today. It last threw one of these a year and a half ago and the t-stat and ECT sensor were replaced as well as the lower radiator hose and while my mechanic was at it I had him flush out all the coolant and put in fresh since he had it opened up. Well now the code is back and I figured I would do a few things to try and figure out if it is the thermostat, temperature sensor or both that are bad. So I reset the CEL with the scan tool my dad has and it is still in learning for the catalyst mon but everything else is cleared out but I know that with the catalyst still learning that it will not throw a CEL for the temperature being too low. But anyway I went for a ride both in the city and on the thruway with the scan tool hooked up so I could watch the temperature graph while driving around. What I noticed was a steady and fast increase in the temperature from 60 degrees up to 183. It never got any hotter than that which I know is wrong. Anyway I was on the thruway and it just started to reach 170 and then it jumped at 170-173 for 2 seconds. And when I say jumping I mean like a very quick flutter from 171, 173, 172, 171 in that order for the 2 seconds it did that. Then I drove some more and it jumped to 174 and then did a very slow climb to 180 and stayed there the whole time on the thruway. I had got off the thruway and then in the city it went up to 181 but again it did another flutter from 180, 181, 180, 181 and then it stayed at 181. Then when I pulled into my driveway and stopped driving but had the engine idling it went from 181 to 183 and stayed there. Now I know the thermostat on the truck normally starts opening at 180 am I right? But that flutter I experienced can't possibly be the thermostat opening and closing. I know they do that but not in 2 seconds. lol.

Some things to note:

1.) I was driving at 65mph on the thruway for 10 minutes before getting off
2.) I was driving at 30mph in the city for 12 minutes before sitting in my driveway
3.) The outside temperature during the drive was 40 degrees fahrenheit and until I pulled into my driveway the heat in the truck was completely turned off.

Here are 2 pictures, one of the temperature gauge in the dash and another of the temperature reading on my scan tool. Both were taken at the same temperature reading.

View attachment 34265

View attachment 34266

 

[The_Roadie]

It's one or the other. But you're obsessing too much since they're adjacent. Change 'em both and don't look back. Not every root cause is worth rooting out. Have you read the Roadie's Guide to Troubleshoot Anything yet?

 

[kickass audio]

Yeah I know but I hate throwing money at a part that doesn't need to be replaced. Especially that damn temperature sensor. My mechanic wanted 151 to get a new one and install it. He does excellent work but damn that is a rip off if you ask me. The thermostat was 54 bucks to put in, parts and labor. Figure that one out. And I am going to try and talk them into just moving the alternator forward and not pulling the battery because I don't want to go through that whole crap of my truck stalling out at stops while it learns the throttle body. All the electronics they put in these damn vehicles makes them such pieces of shit. Pardon my language but it is really annoying. I miss the older cars that were easy to work on.

 

[MAY03LT]

Yep, when I got the p0128 that is what my ECT was reading. I just did the stat. I like to live on the edge.

Since yours was replaced recently, did you check the coolant level? There have been a few (very few) cases of a low coolant level setting a p0128. Don't ask me how that works.

I'd consider those temp fluctuations normal. I'll snap some pics of my ECT data tomorrow.

Figure that one out.

Yeah that doesn't add up.

And I am going to try and talk them into just moving the alternator forward and not pulling the battery because I don't want to go through that whole crap of my truck stalling out at stops while it learns the throttle body.

A coworker of mine does the stat without pulling the alternator. I think he has triple jointed arms. Or practices witchcraft. I tried going through the wheel well once, never again.

 

[kickass audio]

Thanks for your reply Andrew. My coolant is perfect. Sitting for a day or 2 unused and it is right at cold and when I get the engine hot it goes about 1/8 of an inch above cold. The upper hose is nice and hot and the lower hose is warm but not to the extent it would burn me from touching it. I have no smell of antifreeze unless I get up toward the water pump but for some reason that always smells there even after I had the pump replaced it would still have a very faint smell. No cracks in the radiator, hoses, gasket, nothing. I even went so far as to put some paper up under the pump and it was totally dry. Also just to mention it I did check the water pump and that was replaced 4 months prior to the tstat and ECT sensor as it had bad bearings and the clutch was replaced too since both failed. The clutch was really shot, it sounded like someone didn't tighten it up to the water pump pulley when I revved the engine. lol.

I was thinking it would be just the tstat but when I put the scan tool on it and saw that flutter I thought it was a little odd for it to flutter like it did a few times to me and then steady out. Had it not done that I would just threw the money at the t-stat and had it replaced.

Do you think there would be enough room if they just unmounted the alt from the engine and laid it forward a little? I really don't want that stupid relearn crap. That is the biggest pain in the ass with this truck. I don't think mine would be bad to pull the battery on, I already disconnected my fuses between the front and rear battery bank for them tomorrow if they need to disconnect all power. And lets hear someone on here flag this with red tape but when I pulled my TB I did not pull the fuse or battery when I did it. i just pulled it off, cleaned it up and put it back on. It was pretty clean anyway, just had a very slight amount of deposit. Not like my trucks OEM one that was black and had a layer about half the thickness of the throttle plate in just junk.

 

[MAY03LT]

I was thinking it would be just the tstat but when I put the scan tool on it and saw that flutter I thought it was a little odd for it to flutter like it did a few times to me and then steady out. Had it not done that I would just threw the money at the t-stat and had it replaced.

Gotcha. Like I said I'll get you (and future p0128'ers) some ECT data for comparison and we'll go from there.

Do you think there would be enough room if they just unmounted the alt from the engine and laid it forward a little?

I think it all depends on who is working on it. I have ginormous hands and can't get in there without removing the alt all the way. I can't even get in there to upgrade the alt + to batt + lead (I've seen it done firsthand). IIRC on the first one that I did I tried to cheat by rotating it and didn't have much luck. That dude at my work has tiny hands and can get into places that I can't. So if your mechanic can't fit in OJs gloves, he might be removing it.

I really don't want that stupid relearn crap. That is the biggest pain in the ass with this truck. I don't think mine would be bad to pull the battery on,

Yeah it's a PITA. But at least we don't have it as bad as VW/Audi and HAVE to use a hi-end scan tool to do a throttle relearn.

I already disconnected my fuses between the front and rear battery bank for them tomorrow if they need to disconnect all power.

I wish there was more people like you. I can't even get people to leave out their wheel lock key KNOWING that they're going to have their wheels removed. I hate going through peoples personal property.

And lets hear someone on here flag this with red tape but when I pulled my TB I did not pull the fuse or battery when I did it. i just pulled it off, cleaned it up and put it back on. It was pretty clean anyway, just had a very slight amount of deposit.

I don't have any tape so this is the best that I can do.

Not like my trucks OEM one that was black and had a layer about half the thickness of the throttle plate in just junk.

I wonder if we should have a dirtiest throttle body thread.

 

[kickass audio]

Gotcha. Like I said I'll get you (and future p0128'ers) some ECT data for comparison and we'll go from there.



I think it all depends on who is working on it. I have ginormous hands and can't get in there without removing the alt all the way. I can't even get in there to upgrade the alt + to batt + lead (I've seen it done firsthand). IIRC on the first one that I did I tried to cheat by rotating it and didn't have much luck. That dude at my work has tiny hands and can get into places that I can't. So if your mechanic can't fit in OJs gloves, he might be removing it.

Yeah it's a PITA. But at least we don't have it as bad as VW/Audi and HAVE to use a hi-end scan tool to do a throttle relearn.



I wish there was more people like you. I can't even get people to leave out their wheel lock key KNOWING that they're going to have their wheels removed. I hate going through peoples personal property.



I don't have any tape so this is the best that I can do.



I wonder if we should have a dirtiest throttle body thread.

I can get my hand behind there a little bit to disconnect the plug for it but not daring enough to disconnect the charge wires. lol. I know the stock one is a fusible link but my aftermarket charge lead is NOT protected at all. You short that and its game over and the 4th of july under my hood. lol.

They have normal sized hands for a guy, I have hands the size of a woman. Small hands and feet run in the family (keep that comment to yourself I hear the gears turning ) and I have the biggest ones in the family which compared to everyone else are tiny as hell. lol.

I always try to do things ahead of time for anybody working on my truck. Describe the symptoms the best I can, prepare them for the work if I can and all that. The only thing I wish any shop did with my truck was arm the damn thing when they are not working on it. I have a nice system in it and don't need some deadbeat stealing any of it. They can have the headunit though, that thing is a POS. hahahaa.

I am game for the dirtiest throttle body. tbh the guy before me didn't take good care of the truck. Drove it on a gravel driveway that chewed up the flares on the rear door and bottom cover, the transfercase probably was never changed nor were the differentials, the guy took it to jiffylube (they are horrible in my area not sure about yours) for oil changes, there were like 0 parts replaced on it, all OEM parts. The benefits of buying used. Then again I would do it over buying the new trucks you see out now, electronic pieces of shit with 0 room to work on.

 

[limequat]

Wire a 9 volt battery to a cigarette lighter plug. Key off, install into cigarette lighter. Remove main battery. The 9V will provide enough juice to power the various modules keep-alive memory.

 

[{tpc}]

Limequat beat me to it, but just pick up a memory saver somewhere and have them hook it up prior to disconnecting the battery. Then no relearning.

To me, if it was mine, I'd probably just do the thermostat this time around, but if that didn't fix it I'd be cursing up a storm.

Having just done the t stat and sensor, I found it to be a royal pita. Originally I planned on doing just the stat but when I determined how much a pita it really was, I did the sensor too. If course the second time around is always easier, but I still would rather do just about anything else lol.

 

[The_Roadie]

I'm guessing your mechanic uses a Mitchell flat rate data base or something to quote repair prices. And the sensor replacement probably has an error. And I'm also suspicious of all those mechanics who use flat rate data bases, since they never seem to compensate for the savings in time of doing two things in the same area that share a BUNCH of the same prep work. Then they pocket the savings and don't deliver a fair invoice for the hours they put in.

 

[MAY03LT]

Here's some snaps of my ECT warming up. Shown above is the starting point. I did change the zoom during these pics to show better detail.



Gradual increase (normal)



Another normal transition (zoomed out)



Here I was seeing the temp bouncing a little bit (1-2 degrees) during transition.



While it was in this temp range the ECT temp was bouncing, again 1-2 degrees.



Then it got even better.



Once it warmed up, the fluctuations stopped and she was on 201. I consider the temp fluctuations of 1-2 degrees during warm up to be normal.



This part of this post is for me. These pics were taken with my camera showing my tech2, in my truck, with my head unit showing one of my favorite rappers playing. No one has permission to post these pics anywhere other then GMTNation. For you scumbags that have been posting my content on Trailvoy and other internet forums, this means you.

 

[qsp01]

I recently went through this as well. BTW the thermostat on the 4.2I opens at 190. My 2004 Envoy was taking forever to come up to temperature before I changed the thermostat but after it now gets to 210 on the dash before I get a mile from the house on first start in the morning.

Hard to belive that it would go bad again so soon ... did they replace it last time with the right part?

I agree that if they are changing the thermostat as well then the charge for the sensor should be parts plus perhaps 15 minutes labor at most.

 

[kickass audio]

Thank you guys. I called them out on it today and they even admitted to having issues with Napa t-stats and ECT's in an Equinox that they said they worked on for 14 hours and wasted their money on napa tstats before buying GM parts. They are going to get me GM parts this time around. I really think its just the tstat now that you showed me the pictures of the warmup since that is exactly the flutter I had with mine on the scantool. I sadly couldn't zoom out like your tech2 but for it being a cheapie scan tool that can do my transfer case, abs, obd2 and tranny codes its not bad.

They are probably not going to be able to get to it today and will do it tomorrow as they are short a tech and their lot is always full of cars. I have never been by the shop and seen it with anymore than 2 spots open in their lot. haha.

I just hope that the GM tstat and ECT lasts a lot longer than the crappy napa one did. The old one they believe was OEM because the bolts were really in there and showed no signs of being removed, same for the little pipe that mounts to the tstat. If that is truly the OEM one then thats not bad, 112k miles on a OEM tstat and ECT seems pretty stout. I believe the coolant may have been flushed a few times prior to me owning the truck but can't confirm that. The guy I bought the truck from cleans the old crap out when he sells them.

 

[MAY03LT]

I can get my hand behind there a little bit to disconnect the plug for it but not daring enough to disconnect the charge wires. lol. I know the stock one is a fusible link but my aftermarket charge lead is NOT protected at all. You short that and its game over and the 4th of july under my hood. lol.

Yeah I didn't fuse my charge lead either.

They have normal sized hands for a guy, I have hands the size of a woman.

At my old shop I texted this to my coworker who was out on a road test to come and free me.

I always try to do things ahead of time for anybody working on my truck. Describe the symptoms the best I can, prepare them for the work if I can and all that. The only thing I wish any shop did with my truck was arm the damn thing when they are not working on it. I have a nice system in it and don't need some deadbeat stealing any of it. They can have the headunit though, that thing is a POS. hahahaa.

My work is terrified of anything aftermarket. I told them about a triple alt install that I did and they were shook lol

the guy took it to jiffylube (they are horrible in my area not sure about yours) for oil changes

We have a valvoline franchise around here that has a good rep. I send my customers to them because I won't compete with their price.

Then again I would do it over buying the new trucks you see out now, electronic pieces of shit with 0 room to work on.

Me and the wife looked at new Tahoe, what a $55k hunk of plastic shit (no offense to Tahoe owners). She's more realistic now and is looking for a 00-06 model.

And I'm also suspicious of all those mechanics who use flat rate data bases, since they never seem to compensate for the savings in time of doing two things in the same area that share a BUNCH of the same prep work.

I agree that if they are changing the thermostat as well then the charge for the sensor should be parts plus perhaps 15 minutes labor at most.

The scumbag that I work for is like that. If I do an I6 plug change and a coil, they add .3 labor for the coil. The coil comes off anyway so wtf is the .3 for? The coil connectors can be a beeotch but not a .3 beeotch.

Thank you guys. I called them out on it today and they even admitted to having issues with Napa t-stats and ECT's in an Equinox that they said they worked on for 14 hours and wasted their money on napa tstats before buying GM parts.

My work had a Tahoe that burned up 4 napa fuel pumps in under 2 months. Guess what the fix was?

I sadly couldn't zoom out like your tech2 but for it being a cheapie scan tool that can do my transfer case, abs, obd2 and tranny codes its not bad.

It's all good. You're way ahead of the game just by having something that can read data. And the tool that I want to do better plotting/recording starts at $2K.

 

[kickass audio]

Yeah I didn't fuse my charge lead either.

At my old shop I texted this to my coworker who was out on a road test to come and free me.

Hahaha Looks like you really got into a jam there. Did you lose any circulation to your hand? haha.

My work is terrified of anything aftermarket. I told them about a triple alt install that I did and they were shook lol

Yeah most shops dread aftermarket crap because it gets in their way. At least my shop didn't pull the battery when they did my tstat and ECT today. They disconnected the alt and engine ground I put on for the big-3 and then had moved the alternator forward enough to get into there and remove the parts.

We have a valvoline franchise around here that has a good rep. I send my customers to them because I won't compete with their price.

I take mine to a stealership that is nearby but only because their price is not really that much more than if I did it at home. Plus doing it at home plenty of shops will bitch and not accept my used oil....

The scumbag that I work for is like that. If I do an I6 plug change and a coil, they add .3 labor for the coil. The coil comes off anyway so wtf is the .3 for? The coil connectors can be a beeotch but not a .3 beeotch.

Yeah I hear ya on that. I had the same shop do my plugs and coils and they replaced the coil boots for them all and didn't charge labor for it, only parts.

It's all good. You're way ahead of the game just by having something that can read data. And the tool that I want to do better plotting/recording starts at $2K.

I wanted a tech2 so bad but can't justify getting one considering I mainly only work on my truck. My dad only lets me touch his tahoe when he is sick and needs something done on it ASAP. Other than that its always "It is my truck and I do what I want with it" hahahaa.

 

[kickass audio]

Okay so for all the other members out there and for the ones in the future with this problem this was the fix...

I had the shop test the ECT sensor and it was good however as we said before it is right next to the tstat so why the hell not just get it banged out in the same job to save the hassle?

The tstat was bad and was replaced and all is well. The funny thing with the tstat is that it closes 100% when it is cool, I think it might be opening up sooner than the rated temperature? Not too sure on that but it seems likely since I have heat at all times and very fast too when it is warming up.

I now get up about 1/2 tick past 210 (didn't hook up the scan tool to it yet so sorry guys) but my mechanic said he saw it get to 201 and steady out there when he checked it out on the test ride.

And if anyone would like to know the part numbers I used were these:

ECT Sensor:
Brand: AC Delco
ACD #: 213-963
GM #: 19244715

Thermostat:
Brand: AC Delco
ACD #: 15-11006
GM #: 12620112