Check Engine light on 05 Trailblazer

I recently had the check engine ligth come on. I took it to my Firestone shop. They checked everythng, I assume, and said that the thermostat was not functioning properly and that it needed to be replaced. They also said that when they do that, they have to flush the radiator and put in new coolant. I said OK. It cost over 300 dollers. Quesstion: Can that cause the check engine light to come on?

When the CEL comes on, a “code” is set in the computer that can be read to determine WHY the CEL came on…Post that code (example-P1234) and we can tell you more. I can tell you FOR SURE a thermostat can be replaced WITHOUT flushing the cooling system. Have you submitted to this robbery yet??

The repair order said “No drivability problems” They did not list a code so I have learned another lesson. Is there a code that indicates prolems with the thermostat?

A thermostat stuck open will not allow your engine to warm up properly. This will confuse the computer and might set a code that reads something like: Engine temperature not within normal limits-cold".

If the CEL is now off and staying off, they must have done something right…But next time you get a CEL, ALWAYS ask what the trouble code was… Most shops automatically list it on the work-order…

Here is an actual code that might have applied to your problem:

P1117 Engine Coolant Temp Signal Out-Of-Range Low

Thanks. That is what i wondered about. I apprciate the info.

You’re right, they don’t need to flush it. It does have to drained however as the Trailblazer has the thermostat located about mid engine on the side. Most shops won’t put your old fluid back so you have to pay for a drain and fill. I don’t know about the '05, but some models in prior years you had to remove the alternator to get at the thermostat housing so there’s a bit more labor than one might expect compared to a conventional, top/front of the manifold placement.

From now on you can always make sure to ask to have the codes on the invoice. You can also get codes and post them here for advice before having any work done.

This is a 4-5yr old car. As a GM product it probably has DexCool in it. “Officially” speaking GM tells you it can go 5yrs/150K miles before service. I think that is bonkers. So if the cooling system had never been flushed I would actually just be thankful that this episode prompted it. I wouldn’t worry about it.

I’d also make sure to know what kind of coolant you have now. I will guess that it is a yellow “universal” coolant rather than DexCool (orange). (It might look a little orange-ish since it is hard to get all of the old out). If it were me I’d want to know b/c if they got the vehicle off of Dex then I’d keep it off and if you need future service or need to add use the same type that they put back in there.

A lot of the $$ for this probably went to labor for the thermostat, as I am with TwinTurbo - I don’t know which engine you have so I don’t know the specifics but it is probably hellish to get to it.

Thanks for th info. I will make sure of the contents and ensure to keep the info handy in the car.

Just some informstion to help you. If did not already know, autoparts stores will read you code for you at no cost.