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

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).

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Average mileage: 91,137 (8,800–165,000)
Engine affected: 2.0L 4 Cylinder
8 model years affected: 2004, 2005, 2006, 2007, more2008, 2009, 2010, 2013
56 people reported this problem
33 people shared problem details
2007 Mazda Mazda363,200
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.
2005 Mazda Mazda3107,345
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?
2004 Mazda Mazda3130,000
We just keep clearing the code and it stays off till the next long trip I take. It throws code P0126.
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
2008 Mazda Mazda380,000
Had a check engine light and mechanic said it was a stuck thermostat.
2004 Mazda Mazda392,000
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.
2008 Mazda Mazda365,768
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
2004 Mazda Mazda3106,000
CEL code P0126
Failed emissions test: P0126 and P0128. Thermostat replacement $330 to fix.
I have had this thermostat replaced 4 times within the same year, will i have to replace it again. It is getting quite annoying.
2006 Mazda Mazda375,000
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.
2005 Mazda Mazda365,000
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.
I just purchased the car. The check engine light turned on the third time I drove it.
2007 Mazda Mazda380,000
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.
2004 Mazda Mazda343,000
Check engine came on. Pulled codes PO-128. Planning on replacing thermostat and coolant
2007 Mazda Mazda3100,000
replace thermostat
2006 Mazda Mazda341,500
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.
2005 Mazda Mazda3133,000
The check engine light has been on for a few months and it's the thermostat trouble code.
2009 Mazda Mazda330,000
engine light on
2006 Mazda Mazda3144,000
the check engine light is on and the car started shaking yesterday
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