Code P0128- Trailblazer Thermostat Replaced- Engine Light Still On

Question:
2003 Chevy Trailblazer inline 6. In august my service engine light came on. Took it into the shop, they said the thermostat code P0128 was showing back. Then when I go from place to place when I go to start it it acts like it was flooded and took 3 or 4 tries to get it started. Its the 4.2L engine.

I just got it back 2 days ago, had thermostat replaced and that’s not the problem, it's still doing it. If not worse I tried to explain how it starts and they just say they can't promise this is the problem. Truck starts right up in the morning or after it has sit for awhile but to keep starting it like going stop anfd go it does it. It idles good, runs good heater works, great hope this is enough info thanks Dawn. Code P0128 is still in computer.

Answer:
Does the check engine light keep coming on still? If it does when you're having the starting issue, there is still a problem. You'd have to get it checked out again to see what trouble code is present. But offhand, you could have a couple different things causing your problems.

It could be something as simple as a clogged fuel filter or dirty air filter. You could also need the fuel injectors cleaned and possibly the throttle body cleaned out as well. There gets to be a build up of carbon inside the throttle body and that greatly affects how it starts and runs. If you run cheap gas, that can also lead to excessive build up and hard starting.

If the vehicle has a lot of miles, you should consider a tune up too. If there is any smoke out the exhaust when started, that will also tell of a problem. Fuel injected vehicles usually don't flood out unless there is a drastic problem which would be happening all the time, which in your case it isn't.

And your previous thermostat code does cause a Driveability issue when the engine computer can't tell how warm or cold the coolant is. If that code wasn't cleared after repairs, it can still run bad due to it. You will need to confirm the P0128 code is repaired and no longer stored in the computer of your Trailblazer. A simple scan from the local parts store for free will get the codes, no need to take it back to the mechanic.

The code P0128 thermostat code can come back if it was not replaced properly. After replacement, system needs to be purged of air pockets. If the cooling system has air in it, the code can return making you think the thermostat did not fix the problem, when it actually did.

You must run the 4.2L engine with the radiator cap off until the coolant gets very hit and you can see ir running through the radiator fins. Then put the cap back on and run it at about 2,000 RPM for a minute or two. Shut off the engine and let it cool for about an hour. Adjust the coolant level and take it for a drive,then clear the codes.

Question:
2006 Chevy Trailblazer. Have engine Code p0128 ECT which tells me that the sensor has failed. I have a Haynes Manual that shows the location and how to replace it the sensor. My Problem is I followed the instruction and removed the Alternator. The picture in the Haynes Manual shows the sensor next to a big hose. There is a boss casted on the block next to a large hose but there is no sensor. Searched all around that area for the sensor but could not find it. Need help on where to locate the ECT on my 2006 4.2L 6L engine. Every thing is very tight on the left side of the engine. Engine run good but this code keeps coming on the dash. My State makes us have our vehicles inspected each year and it will not pass inspected with this code coming on. Thanks for any kind of help.

Answer:
Well, first of all the code P0128 is NOT a bad coolant temperature sensor. The problem with your truck is you have a bad thermostat. See this link for Code P0128 Thermostat Replacement.