ok so here is my problem... on the way home from work yesterday my ses light came on, so i scanned it today to see what it was and it is the p0128 code. now i know there are other posts on this code but my question here is, they say replace your t stat and it will fix it, but my temp on my guage has not shanged at all once fully warmed up, i know the guage isnt right on but either way the guage always stays right at the 210 mark.. so could there be something else wrong?
engine temp
- Thread starter southpaw84
- Start date
I believe p0128 will set if the engine is too slow to warm up, even if the temp is eventually where it should be. So you may still have a faulty thermostat that is slow to close but not stuck open entirely.
Voymom
Member
- Feb 3, 2012
- 2,523
I would suggest changing out the temp sensor. Make sure your gauge is RIGHT at 210 and not a notch or two cooler, if it is I would also suggest changing the Thermostat.
I believe the sensor is a $40 dollar part, and a Pain in the ass to change. I have to change mine as well because although I don't get an SES code, my truck takes forever to warm up, and the gauge drops with acceleration, and sporadically decides to be at 210. It will eventually get to 210 but sometimes despite how warm it is outside or how hard I drive it, it takes a long time for it to get to 210 which is a classic sign(I have read and been told) of needing a new sensor.
Hope this helps.
I believe the sensor is a $40 dollar part, and a Pain in the ass to change. I have to change mine as well because although I don't get an SES code, my truck takes forever to warm up, and the gauge drops with acceleration, and sporadically decides to be at 210. It will eventually get to 210 but sometimes despite how warm it is outside or how hard I drive it, it takes a long time for it to get to 210 which is a classic sign(I have read and been told) of needing a new sensor.
Hope this helps.
ok thank you for the help, ill prob just replace the sensor and t stat at once while im already working on it
I know on my TBext, it floats anywhere from a tick above the quarter mark on up to 210. Don't get any SES lights so I assume it's normal.
Voymom said:
Please, don't go by the dash gauge when troubleshooting the thermostat or coolant temp sensor. If you have a problem the CEL will illuminate. Unless you have a scan tool hooked up all the time and you are checking the temp coming from the pcm it does checks to see if both the tstat and cts are working correctly for you anyway.
Voymom
Member
- Feb 3, 2012
- 2,523
Rubberman said:
I don't think that's normal
Mine used to do the same, I have pictures. But once I changed the t-stat it was dead on 210 and not 1 notch below or over dead center. Maybe you need a new t-stat too? It's actually a very common thing in these trucks. My Envoy is the LWB too. Before(Bad t stat)
Before(Bad t stat)
After(New t stat)
My t stat never budged until about 2 weeks ago. I changed the t stat out 3 months ago. All I need is a new sensor and it will run dead on again.
In many vehicles, that's true. But in ours, you might be shortening the life of the catalytic converter ($$) and getting worse fuel economy ($-$$$) so it's one of those silent money wasters. Owners often defer fixing these things thinking they're saving money (or at least putting off the expense), not realizing the real story.Rubberman said:
I argue with my PCM over things all the time.CaptainXL said:
Seriously, the PCM is not there to alarm Ma and Pa Kettle (non-enthusiast owners) with hair-trigger CEL events. Note how it smooths the temp data so they don't think the coolant temp goes down even during long downhill coasting. But in this one situation, if raw sensor scan data agrees with a lower-than-210 gauge reading (scan tool will read 170-185, lets say, instead of the normal 185-200), I think there is enough justification to swap the thermostat. Especially if the owner can schedule it for a convenient time instead of the day before their emissions test is due and they've procrastinated and the CEL finally comes on and then they're hating life.
Blckshdw
Moderator
Mine was bad, with no CEL as well
Voymom said:
That's because you drive short distances. The PCM will not throw a CEL for the thermostat until you have been up to operating temp on the highway for a while.
Well. No convincing you guys. I have read the specs for the P series codes and I know what the run parameters are for throwing the code. Got them sitting in front of me right now. Shall i type them out?
Voymom
Member
- Feb 3, 2012
- 2,523
CaptainXL said:
I may not drive from state to state, but I do drive long distances on occasion. The dealership I bought the truck at was 3 hours away. I had made 4 trips there in the truck. I have also made a few 1 hour trips to Iowa city to the mall, movies, and shopping centers. I have also driven to Missouri state line to a smoke shop for cheaper smokes, and that's another hour drive. Plus 30 miles one way to the closest town with all the amenities. All this driving highway mileage with a bad t stat that never caused my truck to put on the CEL.
I do drive a lot of short distances yes, and that is my main driving. But I do drive highway's for long periods of time about 3 times a month.
And I'm not the only person who has not had a CEL come on with a bad t stat or sensor.
I don't see why telling people to change out the t stat or sensor is such a big deal? It's way better to be safe than sorry in my opinion. I would rather change a t stat that is almost out, than wait to spend 800 to 900 bucks buying a new cat, plus t stat and whatever else can go wrong when driving on an expired or close to expired part. But that's just my 2 cents.
If the gauges lie a lot and are not correct on these trucks. What makes you think the PCM isn't the same way? It's a GM truck...come on now!
Voymom said:
Ok, Im just saying most newbies that come here complain about what a pain in the arse the thermostat is to change. Just trying to help them out as best I can. Telling them they need to replace the thermostat prematurely is all I am trying to help them avoid. But yeah us enthusiast its not a problem.
And by the way. You really can't tell the thermostat is bad unless you hook up a scan tool....regardless if the CEL is on or not. If you want to tell the newbie to change their tstat as a troubleshooting proceedure then go ahead. I would rather be precise about troubleshooting and hopefully save time and energy.
Voymom
Member
- Feb 3, 2012
- 2,523
CaptainXL said:
I am a newbie, NEVER in my life changed a t stat....and I was able to figure it out. Changing something a bit early is a lot better than changing them out to late. Plus they don't HAVE to do it themselves, they can take it some place if they want to if they are not comfortable. Plus, just because someone is new to the forum, does not mean they can't do their own work on their vehicle.
As a newbie still, I would rather change a $40 dollar pain in the ass part, than end up spending hundreds of dollars waiting for a definite sign that something is wrong.
I'm also not talking out my ass, I have had the same exact issue with my Envoy. I did change the t stat, and everything was back to normal. Everything is a learning experience for me, I'm not discounting your information at all I'm just saying I have experience in this exact issue and explaining to them what fixed my issue. It's a $40 dollar part, yes a pain in the ass part, but it's way better than ruling out the t-stat and paying for a 800 to 900 cat converter that is even more of a pain in the ass to fix(as a newb). The t-stat is a very common thing in these trucks to go out, so their going to have to replace it eventually, and probably several times in the life of the truck. I know i'm glad that the very first mechanical thing I have ever done was a t-stat and not a cat converter or something to that nature.
That and these trucks are a pain in the ass all together, so I'd say to a newb, to get used to it. I have had my truck for 4 months and have ended up doing way more to it than what a truck should have had done in 4 months. And i'm not even close to being done at fixing everything that is broken either.
Voymom said:
You are apparently mechanically inclined. I was refering to those who are mechanically inclined newbies or who have never opened the hood.
MAY03LT said:
Mine didn't turn on the CEL but it did have a p0128 in the pcms memory. T-Stat was the fix.
That was a pending code. The next few complete drive cycles would have illuminated the CEL.
Voymom
Member
- Feb 3, 2012
- 2,523
CaptainXL said:
I'm not mechanically inclined at all. I never even popped the hood to any vehicle that I have ever owned. I had someone else do it. But with the help of a book, this forum and common sense....I was able to do it.
Just like anyone else can if they put their mind to it.
IF I was mechanically inclined. I wouldn't be here in the first place.
Voymom said:
Lol. I am an ex-air force aircraft mechanic and I still need to come to forums like this. Systems are different for differently designed things. Learning never ends.
Voymom
Member
- Feb 3, 2012
- 2,523
CaptainXL said:
THAT I can agree with lol But just because you have the same system in the same vehicle, does not always mean that those 2 systems run identically. Every mechanical aspect of any vehicle, boat, car, truck, plane is different. My clunking from bad sway bar end links could be someone else's ball joints going out. It's far fetched lol but possible.
I have always and still to this day believe I have a mechanically retarded truck, because EVERYTHING from CEL to the gauges have been different from everyone else's 03 Envoy's and younger more updated ones too.
Learning never ends, and no matter how easy something is supposed to be, it isn't always that way either. And just because a lot of people have had a hard time with one part doesn't mean the next person will have that much of a hard time.
For most of the people here, changing a tire is easy....but I have difficulties doing it. Everything and Everyone is different no matter how much a like we/they are.
MAY03LT said:
No it doesn't because I just made that up. But it's something like that. What does the service manual really say?
So basically what this is saying is if the DTC was set but the CEL didn't illuminate then your thermostat was below 176F for one ignition cycle. In order to set the CEL there needs to be two ignition cycles back to back that fail diagnostics. The ignition cycle needs to meet all the above run parameters listed under CONDITIONS FOR RUNNING THE DTC. Conclusion, you had a sticking thermostat.
Blckshdw
Moderator
Then that makes more sense. My truck was running right around 180F for about a month with the CEL-less P0128 before I got around to getting the t-stat replaced. I'm just glad I decided to mess with my Scangauge when I did, or who knows how much longer I would have dealt with the lower MPGs 
Blckshdw said:Then that makes more sense. My truck was running right around 180F for about a month with the CEL-less P0128 before I got around to getting the t-stat replaced. I'm just glad I decided to mess with my Scangauge when I did, or who knows how much longer I would have dealt with the lower MPGs
Yeah. Anything in the range of 188F - 206F is considered proper operating temp. So anything between 188F and 176F (180 as you indicated) will result in a drop in MPG because the engine is programmed to add fuel and raise RPM''s at a predetermined rate (depending on outside temp) until reaching closed loop.
good morning all,
my temp gauge says 210 however torque reading is any were from 185 to 203 and that's with outside temp at 70 degrees. I take I have gone bad/going bad tstat. I drive about 30 miles each way everyday my heat gets warm but not hot. tstat is in the mail, will replace this wknd. I get no check engine light and based on the info above that make sense.
my temp gauge says 210 however torque reading is any were from 185 to 203 and that's with outside temp at 70 degrees. I take I have gone bad/going bad tstat. I drive about 30 miles each way everyday my heat gets warm but not hot. tstat is in the mail, will replace this wknd. I get no check engine light and based on the info above that make sense.
ac off, set to recycle not fresh air, temp all the way up, this morning it was cold, outside temp was in the 40s, truck took over ten mins to reach normal temp but heat was bearly warm at the vent, after driving for about 20 miles it finally got warm enough I had to turn it down. this wknd replacing tstat, two radiator hoses and purgevalve or which ever one is in the front
neelskit
Member
- Dec 7, 2011
- 69
xj2202009 said:
When the HVAC is set to RE-CIRC, the A/C compressor is running. This is why your heat isn't very warm.
Voymom said:
My temp sensor had an intermittent open circuit that would cause the dummy gauge to be all over the place. You could literally tap the connector and the gauge would instantly show dead on at 210*, only to show ~160* a minute later, then bounce back to 210* again. I also had a few instances where I would shut the engine off and have trouble starting it back up five minutes later because the ECT reported a temp below freezing (open circuit) even though it was 80* ambient and the engine was obviously warm. I never received a P0128 code.
Blckshdw
Moderator