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Error Code P0128

3K views 8 replies 4 participants last post by  Need4Speed2 
#1 ·
Error Code P0128 - ECT Sensor Below Thermostat Operating Range

This is the second time I've had this error code. The last time it appeared was probably 9-12 months ago; I ignored it and it turned off. Now it's back again. Serious or ignore?

Thanks for any input.
 
#2 ·
The code indicates that your engine is warming up too slowly, or not at all. You could have:
  • A bad thermostat
  • A bad coolant temperature sensor
  • Bad temperature sensor wiring or connector
 
#3 ·
OK. Is that a serious problem if the engine is warming up too slowly? I live in southern CA, so we don't ever really have to deal with very cold weather.
 
#6 ·
I want to chime in for a second. It's not necessarily a bad thing as long as it's sticking open...however....a thermostat that is sticking open, can also suddenly stick closed and overheat. I've had many cars were it was stuck and suddenly it released and then stuck closed. As a matter of fact, we were on a family vacation and my parents had a conversion van. I was driving and decided to pull off for gas as we were coming to a construction zone in the middle of nowhere. I had noticed the motor was running a bit cool for a 90 degree ND day, but thought nothing of it as it was quite windy. As I'm filling it with gas, I hear a pop and fluid starts pouring out from the back of the motor. It went everywhere. Apparently as I was pulling off the highway and slowing from 80mph, the thermostat suddenly slammed shut and stuck unbenounced to me as I was looking at how to get to the gas station without getting in the semi's way. We were stranded in a farm town for over 4 hours and had to do some engineering at their local tractor repair facility, which included removing the thermostat for the next portion of the trip...and rigging up a hose by cutting and clamping it to fit till we could get to a major city the next day. So....they can go from sticking open to suddenly sticking closed....just a warning!!
 
#7 ·
Just like the last time this happened, the check engine turned off and has stayed off for several days now. Fingers crossed it will stay off.
 
#8 ·
Update on Error P0128: Finally bit the bullet and took it into the GMC dealer for repair. They replaced the thermostat and cooling system sensor for $1,000. No more problems with check engine light or overheating in heavy traffic.
 
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