Mazda Mazda3 Problems

Check Engine Light/Trouble Code Due to Stuck Open Thermostat on Mazda Mazda3

Problem Description and Possible Solution

Some vehicles may experience Check Engine Light illumination with a trouble code indicating the thermostat is stuck open. The thermostat will need to be replaced with a modified one and there is a software update for the Powertrain Control Module (PCM).

(76 people reported this problem)

Mazda Mazda3 Vehicles With This Problem

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Average mileage: 92,433 (8,800–165,000)
Engine affected: 2.0L 4 Cylinder
8 model years affected: 2004, 2005, 2006, 2007, more2008, 2009, 2010, 2013
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Viewing 1-20 of 36 comments
Check engine light came on during recent cold weather. Took car to Auto Zone to have error code read. Error code returned P0126 and P0128. Checked Internet forums and determine faulty thermostat was most likely the issue. Purchased new thermostat at Mazda dealership for $65.
Replaced part myself. Check engine light now off.
I just bought this vehicle and the engine light came on the day after I bought it!!! Autozone checked it out for me and the code directs us to the Thermostat!!! I noticed the timing belt is older so I will change it as well, the tensioner "pulley" is making a noice so I will take a look at it and hopefully with some grease I can get rid of the noice. I also notice a ratle on the driver's side front end which i'm guessing will be the shocks or maybe tie rod ends?
We just keep clearing the code and it stays off till the next long trip I take. It throws code P0126.
OBD Code P0126 keeps coming on. Probably the thermostat is sticking open although the engine temperature appears to warm up in the proper amount of time even on cold mornings. Once the engine warms up, the temp gauge is near the mid-point between H and C (where it should be). After reading the numerous posts from people who have replaced the thermostat multiple times I am hesitant to replace mine. I wonder if it is really a software issue.
Had to have the thermostat replaced 3 times in the past year and a half average bill for this is $500 nice to know Mazda is doing nothing about this problem
I have had this thermostat replaced 4 times within the same year, will i have to replace it again. It is getting quite annoying.
Check engine light came on. The next day it was off, yet, I noticed the gauge showed that the car was overheating. Noticed coolant was low and battery had corrosion. The battery is new, so I didn't understand why this was happening. After taking my car to Hall, I was charged $69 for a diagnostic and was told it would cost $500 for a new thermostat, reprogramming, and antifreeze.x
Just bought car used and 3 days later check engine light came on. Took to Advanced Auto for code details and was diagnosed as thermostat being stuck open so.... here I am at day 5. Planning to take car to be fixed which dealer will not stand behind. $200 later.
light came on po126 open thermostat. replace thermostat. no more light. new problem is light comes on intermitent for few days then will go away for about 8 months. on off....on off...
last problem is loud noise in rear since i bought car. replaced shocks. few months later same problem. never has gone away. loud ride for passenger.
Had the thermostat replaced twice, check engine light comes on, I take it in and they say it's a thermostat problem, it's ridiculous. Never had another car with a thermostat problem.
CEL came on after about 30 miles of driving after letting car sit for 4 hours after driving for 60 miles. Temps had been in the upper 20's and low 30's. Asked Advance Auto Parts to scan using OBDII and was advised that it was either temp sensor or thermostat. Have not yet sought repair.
My check engine was turned on the fay after I had bought it. Autozone scanned it for me and they said it was the O2 sensor. I replaced it and its still on.