2004 chevy trailblazer i was told to replace the thermostat, then dealer said no on 2004 Chevrolet Trailblazer

the dealer said it may just need oil changed or more coolant that service engine does not mean to replace the thermostat they said it takes a 10,000 dollar machine to read it properly not the one at the auto parts store.

???? any ideas on this issue.
Mountain man1

What is your problem ? Is there waring lamp on?
The reading says service engine soon.?
I just had oil changed about 2 weeks ago dealer says the reset should have been done when oil was changed it was not?????
That does not sound like a maintenance reminder light....It may need to have the system tested for faults related to emissions etc.
1 more answer
If the "service engine soon" light is illuminated in the cluster while the engine is running then you have a concern that needs to be taken care of. The power train control module has a code stored in its memory. If the code is a p0128 then you probably need to replace the thermostat because it is opening before it should. This is a very common problem with the trailblazer equipped with the 4.2 L engine.