2004~2008 Mazda3: P0126 and P0841-FF Codes

CTt3P5

TAD
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2016 GT ST 47A
Well, Murphy is up to his old tricks again. Our son was home from college last week for spring break. He drove the 90 minutes back to school yesterday and today the MIL came on. He has a 2008 S GT hatch 2.5L AT with 186K miles. Wednesday night, I topped off his coolant reservoir with some FL22 as it was just above the low mark as well as his windshield washer fluid.

He went to Autozone where they pulled a P0126 DTC - insufficient coolant temp for stable operation. There was a secondary DTC of P0841-FF - transmission fluid pressure sensor/switch a circuit range/performance concern.

He said the car has been driving/shifting fine so the second DTC is puzzling me. Not sure why it would have been pulled with the P0126? I will ask him to check the fluid level tomorrow.

From what I have found a new thermostat should be the quick and easy fix for the P0126 code.

Any other ideas/suggestions? Given the distance, I plan on calling the shop that worked on the car when he hit the curb last fall to replace the thermostat.
 
Yeah, I found that link when I searched the P0841 code as well. That is what led me to asking him to check the fluid as a first step. His girlfriend ended up picking him up on Saturday and he didn't get back to his apartment until late last night so he never did check the fluid.

Wisely, he walked the couple of blocks to campus for his shift this morning vs driving the car. I called Bastian Tire and they told me that if he can get there by 3pm today they should be able to look at it today. He is going to take it in-between his shifts so they should have it around 1pm.

My fingers are crossed that it is as simple as a new t-stat and topping off of the AT fluid.
 
I talked with the shop earlier. The thermostat is stuck open and the coolant temp sensor is bad. The parts are on order and it should be fixed in the next day or two. They said that they drove the car with their scanner connected and got no secondary DTCs for the transmission so not sure why it showed on the AZ printout?
 
Hopefully, that won't pop up again. That's quite a few miles on that Mazda 3, I guess something is bound to wear out after 15 years.
 
Yes, that is what I am hoping for in reamgards to the AT code. Nope, not going to get too upset. Parts fail after time/mileage.
 
I replaced the thermostate assembly on a 2008 Mazda 3 2.3L for that code and it stayed off.

Those thermostates don't last much past 10 years.

I'm betting the sensor is not bad. They just want to replace it to cover their bases.
 
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