P0126 - Thermostat or Sensor

[rideburton56]

Hi All,

First time on this forum, I have an 06 Mazda with ~75k. Last weekend the MIL came on, so I pulled the code, and did a little research.

Its obviously either the thermostat or the ECT sensor. It seems like most people are doing the thermostat and it worked, but I wanted to throw this out there. The water temp gauge on the instrument panel is indicating properly- starts at all the way cold and slowly works its way up to the middle... perfect. The HVAC also does it's job properly as well, nice and hot on these cold days.

I bought a 6 month membership to alldata DIY (i have worked in a shop for years, and I got spoiled with it lol), and have determined there are two different coolant temp sensors. One for emissions control (so that triggers the MIL), and one for the instrument panel.

I was leaning toward the thermostat (already bought one in fact), but after looking at these wiring diagrams, i am leaning towards the PCM ECT.

Thoughts?

 

[thaxman]

Hey, if you have actual pro experience, I am not going to step on your toes. All I can say is I got the code, replaced the T-stat w/a cheapo vatozone part & have been fine ever since. Seems it was sticking open or partially open, and the ECU didn't like that it wasn't reaching operating temp quickly enough. CEL went away in less than 1 week.

 

[simonnyc]

Hey, if you have actual pro experience, I am not going to step on your toes. All I can say is I got the code, replaced the T-stat w/a cheapo vatozone part & have been fine ever since. Seems it was sticking open or partially open, and the ECU didn't like that it wasn't reaching operating temp quickly enough. CEL went away in less than 1 week.

How did you do that? is it hard to do? I get the P0126 CEL code all the time. I have one of those little handheld devices to erase the code but it's kind of annoying to do it constantly. Thanks

 

[slbenz]

On my 07, when I got the same code, I just replaced the themostat and everything is still fine. I replaced mine at about 75K miles and now have 93K miles without a code issue since.

 

[thaxman]

How did you do that? is it hard to do? I get the P0126 CEL code all the time. I have one of those little handheld devices to erase the code but it's kind of annoying to do it constantly. Thanks

I think I said this over in the engine/drivetrain subforum, but the job is a PITA. You will need all your metric sockets from 8mm to 13mm, b/c I don't remember which 2 sizes I needed, plus the range of short and medium extensions. There are 3 bolts holding it to the aluminum block behind the alternator and deep under the plastic intake. 1 or 2 seemed to be easier to get from above and I think 1 could only be gotten from below. Maybe it was the other way around. I didn't remove any other parts except the hose to get to it, which made the work a "skinny arms only" kind of deal. Lots of blind feeling around, and I suggest you are pretty careful putting the bolts back in since the block IS aluminum and the threads are much less forgiving than on an iron block. I hand-threaded them all until I could no longer move them then snugged them up.
But for real, as long as you have some patience, its a good DIY job. Take note of how much pressure it took to loosen the bolts when they come off, so you don't over/under-tighten them going back on.

 

[kw_da]

How did you do that? is it hard to do? I get the P0126 CEL code all the time. I have one of those little handheld devices to erase the code but it's kind of annoying to do it constantly. Thanks

My poor DYI http://www.mazdas247.com/forum/showthread.php?123805176-Mazda5-with-CEL-P1026-amp-Thermostat-Replacement You can get all the bolts from on top. I would recommend getting a hose clamp pliers to help with getting the hose clamps off & on - one of the ones with a long cable.

GL

 

[Secondtyme]

To answer the OPs question, I agree with your hypothesis 100%. My SGII shows the coolant temp dropping by approximately 40 degrees immediately before the MIL pops on with the 0126. The temp gauge on these cars is pretty much worthless in my experience. Driveability is completely unaffected by this odd little dance that the car seems to do every six weeks or so, and as such I haven't gotten motivated to replace the stat yet. Now the real question is, where the hell is the PCM sensor and how does one go about replacing IT? As an aside, it wouldn't surprise me a bit if the damned thing costs $600 bucks LOL

 

[rideburton56]

Now the real question is, where the hell is the PCM sensor and how does one go about replacing IT? As an aside, it wouldn't surprise me a bit if the damned thing costs $600 bucks LOL

Of course I would try to sound like a smart guy on my first post and be wrong. (doh)

After further review on AllData, even though there are two entries for ECT, one as "ECT" and another as "ECT for PCM", it seems that it was really was one diagram for the location, and another diagram for the wiring harness.

Given that I already ordered the thermostat, i am just gonna do it. It seems like its a part that likes to fail on these cars anyways. If it still throws the code, The ECT is easy enough to get to and replace. I will report back once finished.

 

[simonnyc]

I think I said this over in the engine/drivetrain subforum, but the job is a PITA. You will need all your metric sockets from 8mm to 13mm, b/c I don't remember which 2 sizes I needed, plus the range of short and medium extensions. There are 3 bolts holding it to the aluminum block behind the alternator and deep under the plastic intake. 1 or 2 seemed to be easier to get from above and I think 1 could only be gotten from below. Maybe it was the other way around. I didn't remove any other parts except the hose to get to it, which made the work a "skinny arms only" kind of deal. Lots of blind feeling around, and I suggest you are pretty careful putting the bolts back in since the block IS aluminum and the threads are much less forgiving than on an iron block. I hand-threaded them all until I could no longer move them then snugged them up.
But for real, as long as you have some patience, its a good DIY job. Take note of how much pressure it took to loosen the bolts when they come off, so you don't over/under-tighten them going back on.

Thanks. Sounds like a lot of work I'm not qualified to do. I guess I'm gonna just keep turning off the CEL whenever it comes on.

 

[thaxman]

Thanks. Sounds like a lot of work I'm not qualified to do. I guess I'm gonna just keep turning off the CEL whenever it comes on.

You can keep ignoring the problem. I did for a while. But then it came time to reregister & meant an emissions test. I did the work about 1 mo prior to the test to make sure CEL went off on its own and stayed that way.

Seriously, as long as you don't break things when you get frustrated, this is in anyone's skill level. I didn't even touch the radiator except to add fluid to replace what came out of the hoses.

 

[thaxman]

My poor DYI http://www.mazdas247.com/forum/showthread.php?123805176-Mazda5-with-CEL-P1026-amp-Thermostat-Replacement You can get all the bolts from on top. I would recommend getting a hose clamp pliers to help with getting the hose clamps off & on - one of the ones with a long cable.

GL

I used medium sized channel locks to get the hose clamps off. The angled head works way better than std pliers, and you can use them for about 1000 other things around the house incl holding a nail so you don't hammer your fingers.

 

[kw_da]

Thanks. Sounds like a lot of work I'm not qualified to do. I guess I'm gonna just keep turning off the CEL whenever it comes on.

Might be worth it to get it done. Your engine is not running at the optimal temp ... has your mileage dropped? If you are burning more gas, it may pay itself to get the fix.

 

[kw_da]

I used medium sized channel locks to get the hose clamps off. The angled head works way better than std pliers, and you can use them for about 1000 other things around the house incl holding a nail so you don't hammer your fingers.

That's what I did too, but I figure this https://www.amazon.com/dp/ (commissions earned) would work better. I did buy one after I replaced the thermostat ... so I'm set for next time

 

[Secondtyme]

I was wondering if there are alternative stats available for the 2.3l motor. I would kind of like to have a colder thermostat (opens at 150 instead of 180 or so) in hopes that the lower coolant temps would help lower trans fluid temps as well.

 

[thaxman]

I was wondering if there are alternative stats available for the 2.3l motor. I would kind of like to have a colder thermostat (opens at 150 instead of 180 or so) in hopes that the lower coolant temps would help lower trans fluid temps as well.

I think I just stashed by busted one that threw the CEL. I bet it opened around 150.

 

[Secondtyme]

Stupid modern smarty pants cars! I was just thinking about the fact that the CEL comes on when the stat snaps open at 155 degrees in my car. So a colder stat would basically ensure that every time the stat opens the CEL would come on. That sucks, I mean what harm could really come from running the coolant at 150 degrees all the time?

 

[kw_da]

Stupid modern smarty pants cars! I was just thinking about the fact that the CEL comes on when the stat snaps open at 155 degrees in my car. So a colder stat would basically ensure that every time the stat opens the CEL would come on. That sucks, I mean what harm could really come from running the coolant at 150 degrees all the time?

Looks a like a lot of bad things from http://www.jalopyjournal.com/forum/archive/index.php/t-23677.html

"When an engine runs cold so does its lubricating oil, which means more potential for moisture and acid to form in its oil. At higher temps (both oil and engine) harmful deposits are boiled off. This prevents the slow destruction of bearing material and shortened engine life.
When an engine runs too cold, the fuel economy goes down, often way down. A decrease of 6 to 10 miles per gallon isnt unusual and as fuel consumption increases so does wear. Wear increases because of two factors. First, the cold engine doesnt heat the oil sufficiently and harmful deposits, moisture, and acid accumulate rapidly, then eat away at the inside of your engine."

However, I don't know if 150 deg is considered low.

 

[Secondtyme]

I would tend to think that under 100 degrees would be considered "cold" But then you never know....

 

[simonnyc]

You can keep ignoring the problem. I did for a while. But then it came time to reregister & meant an emissions test. I did the work about 1 mo prior to the test to make sure CEL went off on its own and stayed that way.

Seriously, as long as you don't break things when you get frustrated, this is in anyone's skill level. I didn't even touch the radiator except to add fluid to replace what came out of the hoses.

Will ignnoring the problems create an issue for the car in the future? I have to bring my car in for inspection this week. Will I not pass the emissions test b/c of this issue (even if I clear out any CEL codes prior to bringing my car in)?

 

[kw_da]

Will ignnoring the problems create an issue for the car in the future?

See post #17 - but I don't know if having a stuck open thermostat makes the temp low enough to cause those problems - it probably depends on where you live & time of year (ambient temp).