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P0128 code

7K views 4 replies 3 participants last post by  William81291 
#1 ·
I just got my first check engine light on my coupe the other day. I was just driving to work and it came on, but seems to be running fine. I took it to autozone and it came back with P0128. It says it could be poor electrical connection at CTS, low coolant level or faulty thermostat. I had already checked the radiator and it was full, however the reservoir water line was just above L so I put about a cup of water in it to the full line and started it up and the light is still there. Any suggestions? I know I could call the dealership and make an appointment as I would think it would be under warranty, but they are about 60 miles away and the gas money there and back would be about the same as buying a new thermostat if that turns out to be the culprit. My car only has 18k miles on it. We did have a couple days of sub-zero temps last week if that means anything, but it just came on a couple days ago when it was above freezing.
 
#2 ·
That code is set when the coolant temp does not get up to the proper temperature over a certain time frame.

What does the temperature gauge do? As soon as it moves off the first mark that is around 140F, then each mark is around 10F and it is almost all the way up at 170F. Does the heater put out good heat? Is the upper radiator hose too hot to hold? You could also put an IR laser temp gun on the aluminum pipe next to the ECT to see what it reads. It is located on the back of the head.
 
#3 ·
The heater seems to work fine, although I never do crank it all the way up. I haven't really noticed the temp gauge. All I know is it does move up once it warms up, but I never really paid much attention to what mark it goes to.
 
#4 ·
Well don't put too much faith in it as it really is a glorified idiot light. But it is ran by the ECU using the ECT as s the sensor.

If you can find someone with an OBDII data reader it will show you what the value of the ECT is.

It definitely is under warranty if the sensor is faulty.
 
#5 · (Edited)
Yea I've got the code too. Looked it up and it says coolant thermostat isn't reaching the right temp. Got about 54k miles on my 13 2.0t. Might be a fault ect sensor; radiator fan; or the thermostat stuck open. Brought it back to the dealer to see if it's under warranty and they said yes so I'm going to have them deal with it.

Update: Found out it was the thermostat was stuck open. Under warranty, replaced the thermostat.
 
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