Another P0128

[blazinlow89]

I have the CEl for coolant temperature, it popped up about 3 weeks ago but I did not have a scanner at the time. Finally checked it the end of last week.

I am getting ready to order the parts off of rockauto, they will be all AC Delco. Right now I am looking at ordering the t-stat, upper radiator hose, lower radiator hose. Now for the question, is it worth the extra $40 for me to replace the water pump. I have 118k miles on the truck. Does the 4.2 have w/p issues?

 

[MichEnvoyGuy]

Dont forget to replace the ECT while youre in there.

Also, yes the 4.2l engines have problems with the water pump. Take off the belt and try to wiggle the cooling fan fro/aft. If there is any play, replace the pump. I replaced my original around 125,000 miles. It was making a heckuva racket upon cold startup and had about 1/4" or more of play.

 

[blazinlow89]

Just ordered the stuff from rockauto.com

Picked up both upper and lower hoses, new t-stat, new water pump, ECT sensor, gaskets, and a new fuel filler cap.

$158 shipped.

 

[krivraq]

We blew the water pump last summer @ 65mph, towed home, replaced water pump, coolant and belt only. I questioned the thermostat, but the engine ran fine with no issues, except CEL code #PO128, so I let the thermostat be since it seemed way more involved than the water pump replacement. Many attempts to reset codes since then after other fixes and PO128 still returns.

Now the problem is NJ inspection will not pass me with CEL on. I just failed NJ inspection again after I reset codes in lot before getting on inspection line because "The computer is at zero. You need to drive about 200 miles or so to get the computer to read any codes so I can pass or fail you." ---I know the computer will read codes after driving so many miles, that's why I cleared them--so I could pass inspection!

So, my question is-- "Do I just need to replace the thermostat now or is it more than that?"


Thank you in advance

 

[gmcman]

We blew the water pump last summer @ 65mph, towed home, replaced water pump, coolant and belt only. I questioned the thermostat, but the engine ran fine with no issues, except CEL code #PO128, so I let the thermostat be since it seemed way more involved than the water pump replacement. Many attempts to reset codes since then after other fixes and PO128 still returns.

Now the problem is NJ inspection will not pass me with CEL on. I just failed NJ inspection again after I reset codes in lot before getting on inspection line because "The computer is at zero. You need to drive about 200 miles or so to get the computer to read any codes so I can pass or fail you." ---I know the computer will read codes after driving so many miles, that's why I cleared them--so I could pass inspection!

So, my question is-- "Do I just need to replace the thermostat now or is it more than that?"


Thank you in advance

Generally the ECM won't give you a "green light" for emissions until you have completed a set number of driving cycles. If you are having the P0128 code, you either have low coolant temp or a bad ECT telling the ECM the coolant temp is low...or both.

 

[gmcman]

Blazinlow....the 10 min to cut this with a dremel or even quicker with a larger cutoff tool, will net you some sanity. Snap-on sells one for about $40 but if you have an extra 18MM deepwell laying around, I promise you it will be your friend.

Wanted to add, just remember to disconnect the sensor lead first.

 

[krivraq]

Generally the ECM won't give you a "green light" for emissions until you have completed a set number of driving cycles. If you are having the P0128 code, you either have low coolant temp or a bad ECT telling the ECM the coolant temp is low...or both.

Thank you, GMCMAN. Perhaps I may be dealing with a bad coolant temperature sensor?--Because when the water pump blew, the coolant temp was pinned at maximum. That's why I thought about replacing the thermostat, but it seemed to function properly after all work was finished.

Is the cut-away 18mm socket picture for replacing the coolant sensor?

 

[Mark20]

Thank you, GMCMAN. Perhaps I may be dealing with a bad coolant temperature sensor?--Because when the water pump blew, the coolant temp was pinned at maximum. That's why I thought about replacing the thermostat, but it seemed to function properly after all work was finished.

Is the cut-away 18mm socket picture for replacing the coolant sensor?

Jumping in for gmcman, yeah the cut out socket is for the coolant sensor. Makes it into a O2 sensor like tool. If I have to do my coolant temp sensor again, I'm buying a cheap 18mm socket and taking my angle grinder to it.

 

[MichEnvoyGuy]

I used a wrench, yes it was slow at 1/2 turn each time, but it saved me from cutting up a good socket!

 

[krivraq]

Thanks. I have both socket and wrench, I'll figure it out.

So do I need the Coolant Temp Sensor, thermostat, ECM, or something else to put an end to this PO128???

 

[The_Roadie]

So do I need the Coolant Temp Sensor, thermostat, ECM, or something else to put an end to this PO128???

It's almost always just the thermostat. While you're in there, you may consider changing the sensor as well because it's only a little bit more work, but diagnosing WHICH item it is can be difficult ahead of time. Statistics suggests it's the thermostat, by maybe 20-to-1 margin.

By deferring the thermostat replacement until you had to pass emissions, you haven't just been living with an annoying P0128 code and SES light. You've been losing 2-6 MPG of fuel economy that could have LONG SINCE paid for a mechanic to just fix it. And you've put your catalytic converter at risk of damage that could cost another $200-600 to fix. Good luck.

 

[krivraq]

Well then, it seems a bit obvious what the rest of my weekend is about. Probably into the midnight hour because if I remember, the thermostat is buried within the head or at least I'd have to remove most of the top-end of engine???

Thanks again, Roadie, for your expert insight on this matter and the air pump issue last fall that led to the link to the new site.

 

[blazinlow89]

Blazinlow....the 10 min to cut this with a dremel or even quicker with a larger cutoff tool, will net you some sanity. Snap-on sells one for about $40 but if you have an extra 18MM deepwell laying around, I promise you it will be your friend.

Wanted to add, just remember to disconnect the sensor lead first.

Hmm, nifty. I wonder what the harness size is. I have a set of the craftsman universal drive sockets that have a through design. The hole in the center is about 3/8" maybe even 1/2". Even a snip and splice might be in order.

Thanks for all the info guys, hopefully this will all be in this week, so I can do it this weekend. I forgot too all Delco parts, except the gas cap.

 

[MichEnvoyGuy]

Well then, it seems a bit obvious what the rest of my weekend is about. Probably into the midnight hour because if I remember, the thermostat is buried within the head or at least I'd have to remove most of the top-end of engine???

Thanks again, Roadie, for your expert insight on this matter and the air pump issue last fall that led to the link to the new site.

The thermostat can be accessed through the wheelwell or from atop. The only thing that needs to be moved is the alternator. Its not that bad of a job, comparatively speaking it is a PITA but it takes me about 45 minutes to change out the t-stat on my Envoy.

 

[The_Roadie]

...if I remember, the thermostat is buried within the head or at least I'd have to remove most of the top-end of engine???...

God, no. The designers did us no favors, but that would have put it into the territory of the truly evil.

View attachment 19271

 

[krivraq]

I've been reading around the past few mins and noticed the thermostat and temp sensor locations. As well as the PITA lower therm bolt and alternator issues. Already called the local parts dudes and I'm now off to do some dirty work. I'll check the current temp gauge position while driving over and back to check that as well.

Thank you greatly, Everyone!

I'll be back later, hopefully with some swell news....

 

[krivraq]

Oh man, no one wants to be this guy. It went from bad to worse. Swapped out thermostat today and the old CTS came out no problem. Upon installing new sensor, was tight all the way because of the thread sealant and got to the last thread showing and SNAP!!! Thought I only broke the 18mm socket I just made for the sensor install, but it was the POS aftermarket sensor that broke off in the block. Now I'm screwed. Gonna take some careful drilling and tapping to get by on this one.

This truck just kills me.

 

[blazinlow89]

Go to autozone, advanced, o-however the hell its spelled, and rent a screw/bolt extractor set. If not you will be purchasing one from Lowes, Ace, Home Depot, True value ETC. I would highly advice against trying to drill out the sensor, as extra metal in en engine = more headache. Take that one back wherever you bought it and demand a refund and pick a NEW AC Delco one. God knows our engine's run like hell when they do not get what they want, It is worth the extra 5-10 bucks to purchase a quality part.

It took me about 7 hours to do this along with the water pump, temp sensor, t-stat, new hoses and a flush. We also did the rear brakes, because of a screw up with the caliper. Truck runs nice, had a leak due to some oversight, but every looks good now. Temp runs at 206* through torque.

 

[MichEnvoyGuy]

Oh man, no one wants to be this guy. It went from bad to worse. Swapped out thermostat today and the old CTS came out no problem. Upon installing new sensor, was tight all the way because of the thread sealant and got to the last thread showing and SNAP!!! Thought I only broke the 18mm socket I just made for the sensor install, but it was the POS aftermarket sensor that broke off in the block. Now I'm screwed. Gonna take some careful drilling and tapping to get by on this one.

This truck just kills me.

Hang in there, I broke off a t-stat housing bolt into the block in December. Good news is it was a lot easier to get the broken piece out than I originally thought.

Any pictures of the broken sensor?

 

[krivraq]

The brief rundown...

The truck is sitting in the barn at my parents' about 100 miles away right now, my father is a certified master mechanic/auto body, expert witness, etc. with all the necessary tools and toys to get just about any job done, and my time is limited here with work so all repairs will need to wait until next weekend at the earliest. So anyway, it went from driving up Saturday to replace the thermostat, CTS, left front axle seal (again), left front wheel bearing hub (again) and an oil change to finding the front brakes and rotor needed replacement (obviously again) and the right, lower tie rod end worn out. Found out I had the wrong axle seal (read all the posts regarding this issue afterwards, got correct one at dealership today) and snapped new CTS in block and that pretty much ended everything with a bang. I did get oil changed, new wipers, new thermostat, new rotor and pads installed so it wasn't a total waste of time, just a VERY expensive weekend.

I wanted to take pictures of all the processes for posting, but I was quite greasy for using a camera every step of the way. I don't have a picture of the snapped CTS, my spirits were completely shut off the moment it broke as I knew the reality instantly. Using an extractor is our first gameplan, but with the torque required to install it to that point, we don't think it will be that easy. If necessary, we'll drill out with shop vac hose at drill point and if necessary, run compressed air into radiator to blow out any close-by particles back out of hole or even fill radiator back up with coolant to allow gravity to fill block back up and flush out through hole, as long as the surface tension hasn't been broken and those filings are still floating.

MichEnvoyGuy, how did you get yours removed??

 

[MichEnvoyGuy]

MichEnvoyGuy, how did you get yours removed??

Well, thats just the thing.

My situation varied a little from yours in that my t-stat housing bolt broke off. Luckily, there was 1/4" (maybe) of broken bolt extruding from the engine block. I called a friend over and he went to town with viscripts, my propane torch and beer...lol. I was far too stressed out at that point to try myself and knew if I took two steps back from the situation that it would prevent me from doing any more f-ups. I could just imagine myself breaking the already broken bolt off flush with the block Thank God that didnt happen and my friend was able to get the broken bolt out, 1/8 turn at a time, out of the block. ((whew)).

I shouldve knew something was up, the t-stat bolt was going in kinda tight but I didnt think it was unusually tight so I just kept ratcheting along. Then <<SNAP>>. Lesson learned.

Are there any pics of your broken sensor? If we saw the exact situation maybe we could make suggestions for ya.

 

[krivraq]

... I broke off a t-stat housing bolt into the block in December. Any pictures of the broken sensor?

I missed that one about it being a thermostat bolt. In my case I wish it was a bolt that broke off flush because if I drilled it out, it wouldn't be into the water jacket. In the meantime, maybe I can get my father to text a picture of the broken sensor, since I can't there until Saturday.

 

[krivraq]

One half...
View attachment 19534

And the other half, a little shiny from the flash, but there isn't anything to see really...
View attachment 19533

 

[krivraq]

Okay worse is worst...

Drilled broken ECT sensor to use hardened-steel bolt extractor, extractor broke, now trying to drill out and nothing working, not even cobalt bits. I will gladly place this POS/PITA ENVOY for sale as is before I bring it to dealer to have broken ECT sensor drilled out and tapped/replaced for +$1000 when they insist they have to pull out engine to work on it.

Soooo, what resistance does the sensor read when in normal operating temp? I'm thinking about placing a resistor across ECT sensor wires to trick PCM. Will this royally screw up everything?

Also, is anyone selling Hindsight??? I'll pay top $$. I should have just left the old ECT sensor in and tested cluster gague after replacing the thermostat and hoped for the best. Sorry to be so down, but this is basically a self-inflicted issue. Thought I was doing the right thing.

 

[MichEnvoyGuy]

Okay worse is worst...

Drilled broken ECT sensor to use hardened-steel bolt extractor, extractor broke, now trying to drill out and nothing working, not even cobalt bits. I will gladly place this POS/PITA ENVOY for sale as is before I bring it to dealer to have broken ECT sensor drilled out and tapped/replaced for +$1000 when they insist they have to pull out engine to work on it.

Soooo, what resistance does the sensor read when in normal operating temp? I'm thinking about placing a resistor across ECT sensor wires to trick PCM. Will this royally screw up everything?

Also, is anyone selling Hindsight??? I'll pay top $$. I should have just left the old ECT sensor in and tested cluster gague after replacing the thermostat and hoped for the best. Sorry to be so down, but this is basically a self-inflicted issue. Thought I was doing the right thing.

Whoa, whoa whoa....lets not start punching babies just yet....

Have you thought of this: Now before I start, let me just say I grew up in Metro Detroit where we are KING of jerry-rigging things (sometimes) in very clever ways!

What I would do: Leave the broken ECT in the block, ta hell with it. Get a 4-5" metal piece of pipe that will fit tight into your lower radiator hose close to your engine. Have a bung welded on to it, or do it yourself, I dont really care. Screw the ECT into the bung. Tighten the hoses onto the pipe and voila!

The coolant coming OUT of the engine at that point is as hot as the coolant in the water jacket, the ECT shouldnt be askew at all.

You can thank me later

 

[gmcman]

I agree with Mich but did you already drill through the sensor completely, is it leaking coolant? Can you post a pic of what you are working with as of now?

If you are at the point of no return, I would take a small cobalt bit and go real slow, clearing the drill bit as much as possible and make a series of small holes from one side to the other. I had to do this once to help a buddy out and we started in the center and made a slot long enough to get a good snap-on flathead screwdriver that had a hex at the base of the handle to utilize a wrench to get torque on the screw driver.

That method worked and if it didn't then we were going to go all the way across and pry one half of the sensor away from the threads. You can probably lower the AC compressor to gain more room, still leaving the hoses intact.

Edited to add we obviously couldn't drill one long slot, we made each hole as close as we could then pushed the remaining material away with a small screwdriver...driving it into the sensor just enough to get it out of the way.

 

[Voymom]

Okay worse is worst...

I will gladly place this POS/PITA ENVOY for sale as is before I bring it to dealer to have broken ECT sensor drilled out and tapped/replaced for +$1000

I got dibs!!! I'll give ya $500 for it

 

[krivraq]

What I would do: Leave the broken ECT in the block, ta hell with it. Get a 4-5" metal piece of pipe that will fit tight into your lower radiator hose close to your engine. Have a bung welded on to it, or do it yourself, I dont really care. Screw the ECT into the bung. Tighten the hoses onto the pipe and voila!QUOTE]

I was thinking about something like that on the long drive home tonight, something I could put inline with the coolant flow, but wasn't quite sure where to place it. I'll go to the drawing board with that one.

I'll thank you now

...did you already drill through the sensor completely...
If you are at the point of no return, I would take a small cobalt bit and go real slow....

The coolant was already drained last weekend when I replaced the thermostat. Don't have a picture, but yes, we drilled an 1/8" pilot hole with cobalt bit through center of sensor into block. That was a 1 hour round trip to local hardware store for new bits and almost impossible to get it drilled with two 1/8" bits. Then the larger 7/32" bit broke instantly and 21/64" bit just gets stripped as soon as it hits the edge of the pilot hole where it meets the hardened steel. The area has been cleaned and will be "plugged" with JB-Weld for now--maybe for good if I'm able to use the "bung method".

I got dibs!!! I'll give ya $500 for it

That only covers my cost for parts the last two weeks, not including our misery and labor.

 

[MichEnvoyGuy]

I was thinking about something like that on the long drive home tonight, something I could put inline with the coolant flow, but wasn't quite sure where to place it. I'll go to the drawing board with that one.

I'll thank you now

You'd want to place it in the stream right after the thermostat and not too much further because the you want the ECT to be submerged in coolant that is the closest to the temp as the water jacket as possible. This can possibly be a cheap and relatively easy fix with my method. That is, providing, the broken ECT isnt leaking because of the pilot holes, etc... because then you would have to do something with the broken ECT afterall.

 

[gmcman]

I think you are stepping up the bit size too quickly. Take smaller graduations and you will eventually get it.

 

[krivraq]

You'd want to place it in the stream right after the thermostat and not too much further because the you want the ECT to be submerged in coolant that is the closest to the temp as the water jacket as possible.

My Dad's been working on that custom fix. He welded a nut to a piece of fence post, perfectly fits the diameter of the radiator hose by the way, and placed it inline next to the thermostat. After driving around for a bit (no leaks from JB-Weld on pilot hole through broken sensor), the temperature gague barely even moves from "cold" on what should be a "hot" engine--except when climbing a long hill then it shoots back down to "cold". Come to find out, coolant flows from radiator into thermostat through bottom hose, not the other way. ECT sensor is now reading cooled coolant from the radiator. Now after replacing new bottom hose, he's going to try and put that pipe into top radiator hose, much more difficult given the length is much shorter.

Any feedback on the ECT position? I have read here that there is only 1 ECT sensor, is this correct or is there another that may be swaying this coolant reading??

It's official, I now hate this truck

 

[gmcman]

Hopefully someone can chime in on what the absolute minimum temp is required by the ECM to establish "Normal Temp". That being said, obviously that will be your target temp, I would tap the heater hose leaving the block, more constant temp and likely more accurate...try to get as close to the block as possible.

This is an idea of what I would try.

Auto Meter 2280 - Auto Meter Radiator Hose Coolant Adapters - Overview - SummitRacing.com

 

[krivraq]

Thank you. That's pretty much what we custimized from fence post stock and a 12mm threaded nut. The Summit one is 5/8" though. We'll have to wait and see how ours turns out after switching the piece to the upper radiator hose.

 

[gmcman]

I would try to use the heater hose since I believe it's a constant flow.

 

[krivraq]

Yeah, when I saw the 5/8" diameter fitting it looked like it would be for a heater hose. Thank you for the link, I've already forwarded it to my father since he's doing the work for me now since I'm back home for the work week.

I just can't wait to finally post that this project is completed and all is functioning properly! (Because then I can finally get this truck through inspection and start to fix my car to pass inspection: '94 Camry V6 274,000mi)

 

[Enderbygrandpa]

you would need to put bung in upper hose to show hot temp lower hose comes from rad temp will be cool.