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).
Car Problem Reports
Mazda Mazda3 Check Engine Light/Trouble Code Due to Stuck Open Thermostat
Mazda Mazda3 Problem
Average Mileage: 87,017 mi (50,000 mi - 130,000 mi)
Visitor, 2008 Mazda Mazda3
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
Visitor, 2004 Mazda Mazda3, 92,000 mi
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.
Visitor, 2004 Mazda Mazda3, 130,000 mi
We just keep clearing the code and it stays off till the next long trip I take. It throws code P0126.
Visitor, 2004 Mazda Mazda3, 106,000 mi
CEL code P0126
Visitor, 2007 Mazda Mazda3, 83,037 mi
Check Engine Light / Due to malfunctioning thermostat
Cost $385 for repair at Dealership. 12/3/13
Visitor, 2008 Mazda Mazda3, 80,000 mi
Had a check engine light and mechanic said it was a stuck thermostat.
Visitor, 2005 Mazda Mazda3, 107,345 mi
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?
Visitor, 2005 Mazda Mazda3, 110,000 mi
Check engine light came on and repair shop says the Thermostat is stuck open and needs replaced. Estimate is a couple hundred bucks...Will see if I can do it myself...
Visitor, 2004 Mazda Mazda3, 70,000 mi
Takes a long time to warm up.