2007 Mazda Mazda3 Check Engine Light

My 2007 Mazda 3 keeps showing a check engine signal.
When it originally came on I took it to the dealer who identified the problem as a defective engine thermostat.
When I went to pick up the car the signal was off.
It stayed off for a couple of weeks.
Then it went on again.
The check engine light comes and goes.

The dealer service supervisor originally said that no damage would occur if the check engine light was steady ( It is ) but that if it blinks it can be a major problem.
I am confused.
In the past I have changed thermostats myself. It was easy and cheap.
Now, I understand, it is an expensive fix.
What do you recommend?

You need to find out why the check engine light is on. Many parts stores will read them for free. But don’t buy parts until you post the codes here. They look like P0123. Or you can take it to your mechanic and he’ll take care of it. There are dozens of things that cause the check engine light to come on.

Sounds like you didn’t have the thermostat replaced.

The thermostat is a known problem for the 2007 Mazda3. It is an unusual system with the expansion tank having a bigger than usual role, making the bleeding of trapped air an issue after the thermostat is replaced. I found instructions online and did the job myself a few years ago. Just a warning that this job is not the old-school $5 thermostat replacement. It probably took me three hours when I did it, so a shop should do it in two.


Just in case you don’t know on the right of your screen there are dates of the last post. In this thread it was May 2019 .

I just spotted that also. I’m new here. Maybe my answer will help someone else. Thanks

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