Hello friends,

I have had my 2022 CX-5 (57,500 miles) for about 3.5 years now and it has been a pleasure. I am moderately automobile knowledgeable as I was a tech many years ago. I'm no longer in the industry but continue to do my own basic maintenance. I don't pretend to know the ins and outs of all modern vehicles as I don't have time to keep up with all the changes and innovations. I had my car in for a visit today and wanted to share and get some feedback. I'll try and be brief as possible and I will attach today's work order as I know Calisto likes to see that

In early 2024 at 38,000 miles I had a check engine light come on. The coolant temp guage was about halfway between the cold and 210 line and I had been driving over 30 minutes. I scanned it and found code P0126. I made an appointment and my dealer took care of it by replacing the coolant control valve under warranty. Everything was fine following the repair.

In early December 2025 at about 57000 miles I noticed the coolant temp gauge wasn't reaching the usual position during drives. No light, no codes, heat seemed normal. I figured maybe it was just cold out but considered maybe the thermostat was starting to get stuck open again. Two weeks later I was on the freeway and the engine light came on solid. When I scanned it at home it was P0126 again. I made an appointment which was yesterday. This time they did a different repair and I had a great chat with the mazda tech that worked on my car. According to him after replacing a bunch of coolant control valves (then apparently the thermostat inside later on) Mazda was seeing a lot of comebacks and changed the repair again. Now they remove coolant control valve, disassemble, then remove the thermostat and install a dummy plug. They noted the new bulletin (attached) on my paperwork. This is where I have questions and interest. I got the car back, temp is back to where I have always seen it and everything is normal... I'm just interested in what Mazda has done here.

The tech said the thermostat (which is inside the coolant control valve) is now removed and replaced with a dummy plug. He said the whole coolant control valve is basically a big overengineered thermostat now. So what is the design of this thing? How was the thermostat integrated and what benefits did having both have? Were they trying to regulate engine temp more closely by having multiple passages controlled by the coolant control valve AND thermostat? He also said mazda was replacing coolant control valves for a long time which was a temporary patch while they figured it out and "hopefully now they have". Have they? LOL

I want to be clear my Mazda dealer has been great to me the whole time. I was given loaner(s), they are super friendly, and I really like being able to chat with a tech occasionally.

 

Welcome to the forum

 

Good luck with your journey with this thread and its subject line .

 

My understanding (opinion) is that the PCM programming is the major change.
I'm not an automotive engineer, but I'm very familiar with programming.
Reprogramming is needed to account for the removal of any system part/piece that is being monitored by a computer system.
In your case the regulated part being replaced, is being replaced by a "dummy plug" which cannot be monitored.
You would have to ask Mazda engineers to get the factual reason why they are doing this.

 

Bingo for the WIN!
You can actually see this by comparing the 2 ECU internal program sizes before and after the Pass-through.
Now the specific area's it would take even me likely a few dozen hours of comparing all the PIDS to first find the altered ones and then mapping them all out to see that actually reporting to sensors effects. *Mazda is not going to divulge this and no one is going to want to take the time to do this. Its a real PIA and you need an aftermarket ECU calibration program to even begin to do this.
As far as how many effected Mazda's I called my contact with Mazda corp est 3200 approved dealer credited for the TSM service. This means nothing as far as how many were actual needing the service only that the dealer got reimbursed for the warranty service.

The reason I know so much about this because my Mazda VIN was in the report but I was not effected by it.

 

Welcome to the forum to you also Callisto!

 

Thank you for the response, Lobstah. The tech didn't know much about the programming update nor would I expect him to. He just does what the service instructions dictate. I am more wondering about the design of the coolant control valve and how it functions without a thermostat inside it and what speculation there might be about why mazda made a decision to have a coolant control valve with an integrated thermostat that can still function as a thermostat without a thermostat. It sounds funny but I am no engineer.

 

Its to regulate more closely the operating temperature to keep the emission at their lowest. (this by the way is your true answer and as simple as it gets)Because most Mazda's now are below requirements the use of that type of water temperature control may no longer be used.
What I can without stating where the information came from (maybe Mazda powertrain engineer) is that cooling system design controls a more linear temperature regulation. Note more then 10,000-20,000 possible effected vehicle the service was less them 3200 and it really is questionable if all those were reported to be tested for by a Warranty approval service through Mazda corp. This is semi common practice on any service bulletins. And again if you were in the Mazda service employment and assigned to check for a warranty based on a service bulletin you would know and understand their. That service bulletin only that they met the criterion of VIN application and customer complaint to warranty the service is some perimeters showing the possible problem was present. If you understood the service bulletin which I am sure you read the part on each page whom they were written for and you are not one of them the first service was the PCM flashing. Did you even if you could read the MGSS bulletin ? If you did why didn't you mention what it stated?
Now if you want to talk about thermal dynamics and the operation of the CAT temps , operating temperatures, control of the oil and coolant ECU calibration programing etc., then these would also need to be included in talking about in this thread as well.. To what end? lol


Bottom line if you don't completely understand these and have an automotive service background then you basically really have no clue about the service bulletin and how they are written and for whom?



Btw newbie ... I am an Engineer specifically in the automotive industry among other attributes.

 

Seems to be they haven't figured it out. If they did they wouldn't have 6 superceded bulletins.

 

The revisions regarding the (any) service bulletins are because different mechanics are upgrading the service procedures by sending them in to Mazda to be published to the dealership service departments. Very common regarding many of Mazda service-related bulletins. It has nothing to do with the exact solution to many concerns reported by customers to Mazda service departs> In this case only a probable remedy that IMHO seems more ECU calibrating related the hard parts? But as I have not yet been assigned by Mazda a service bulletin related mentioned in this thread to perform on a customers Mazda, I cant make a informed comment based on practical service experience regarding it only what I read and understand how the service bulletins are created and treated regarding warranty work. I can state that it is a nontechnical based service and most any generally experience mechanic or Mazda factory trained Mechanic can perform with no specialize equipment or tools.