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).
Check Engine Light/Trouble Code Due to Stuck Open Thermostat on Mazda Mazda3
Average mileage: 93,630 (8,800–196,574)
Engine affected: 2.0L 4 Cylinder
52 people reported this problem
33 people shared problem details
2007 Mazda Mazda363,200Visitor
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.
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
2004 Mazda Mazda3130,000Visitor
We just keep clearing the code and it stays off till the next long trip I take. It throws code P0126.
2005 Mazda Mazda3107,345Visitor
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 Mazda392,000Visitor
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.
2004 Mazda Mazda3106,000Visitor
CEL code P0126
2008 Mazda Mazda365,768Visitor
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
2008 Mazda Mazda380,000Visitor
Had a check engine light and mechanic said it was a stuck thermostat.
2005 Mazda Mazda365,000Visitor
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.
2005 Mazda Mazda3196,574Visitor
Check engine light on but has no code
2006 Mazda Mazda3120,000Visitor
check engine light came on. checked fluids. will take it to auto zone later today.
2007 Mazda Mazda364,000Visitor
Stuck thermostat open. Had it replaced. Now trying to figure hou to turn check engine light off.
I just purchased the car. The check engine light turned on the third time I drove it.
2009 Mazda Mazda330,000Visitor
engine light on
2004 Mazda Mazda3Visitor
Failed emissions test: P0126 and P0128. Thermostat replacement $330 to fix.
2006 Mazda Mazda3144,000Visitor
the check engine light is on and the car started shaking yesterday
2007 Mazda Mazda380,000Visitor
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.
2006 Mazda Mazda362,000Visitor
My mechanic replaced the T-stat and now, 4 weeks later, the light is on again.
2004 Mazda Mazda343,000Visitor
Check engine came on. Pulled codes PO-128. Planning on replacing thermostat and coolant
2005 Mazda Mazda386,250Visitor
I replaced thermostat and coolant
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