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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.