P0128 Code.

tony890721 · February 3, 2011

I have a P0128 DTC on my 2007 Silverado classic with 4.3 V6 engine. The truck had the MIL came on Sunday then by Tuesday, it turned off. What can I do to fix this problem. The truck runs fine nothing really seem wrong with it, just this code is bothering me and I want to get it taken care of ASAP within 2 days because I have to go to work on Monday and I won't have time.

Additional Info:

The truck has 31K miles on it, the engine hours is now at 1.3 (weird), the temp gauge stays around 2 part to the right of the 160 mark during normal operation.

gmtech4 · November 11, 2014

Do you have pictures of where is this thermostat housing is located? And also what are the torque specs for tightening the thermostat housing?

It seems that you have zero experience doing anything on a veh , just do yourself a favour and take to a garage or a buddy

dcheeseman · February 3, 2011

Thats a coolant temperature sensor thats reading below specs. Basically the engine didn't warm-up within the allowed normal time, which threw the code. Sounds like a bad thermostat, probably stuck open or opening too soon. Drain coolant, replace thermostat and refill with new coolant. This should fix the problem. Not 100% until I see the vehicle for myself, based on what I know this is what I believe is your probably, pretty cheap fix though. Hope this helps!

Daniel

tony890721 · February 4, 2011

Well how can I determine that it's a bad thermostat or bad coolant sensor? It's been so long since I've studied about cars in high school.

dcheeseman · February 4, 2011

Well how can I determine that it's a bad thermostat or bad coolant sensor? It's been so long since I've studied about cars in high school.

Well in can be either or, most likely its the thermostat. Well does the truck warm-up to normal operating temparture and if it does how long does this take, seem longer than normal (Of Course a cold day will take a little long vs a warm day). Once the engine has been running for a while squeeze the radiator hose, should be pretty tight from pressure (This should be the top radiator hose not the bottom one). If it doesn't warm-up all the way after drive the truck for 15 minutes or so than, I would replace the theromstat, flush the coolant and see if this fixed the problem. Try this next. Hope this helps

Daniel

tony890721 · February 4, 2011

Also how do I replace the thermostat and drain the coolant because I don't see the drain cock anywhere for this truck.

dcheeseman · February 4, 2011

Also how do I replace the thermostat and drain the coolant because I don't see the drain cock anywhere for this truck.

Should be on the bottom right or bottom left of Radiator, let all drain out, replace plug, remove thermostat housing and hose, replace new thermostat and fill with new coolant and let truck warmup all the way and check coolant overflow tank. Than fill as needed to the hot mark.

tony890721 · February 4, 2011

Do you have pictures of where is this thermostat housing is located? And also what are the torque specs for tightening the thermostat housing?

RocktyTop1911 · November 10, 2014

Late post but just wanted to add my experience. I also received this error (P0128). Turned on my AC and received error on my display stating Engine To Hot Turning Off AC. The Truck was cold at the time. Ran a diagnotic and got the P0128 code. Had mechanic flush radiator since it had been 5 years and replace the thermostat. So far, no problems. I have a 2009 Sierra 1500 WT V6 with 36000 miles.

Posted these comments in another thread:

I also started experiencing the steering groan on my 2009 Sierra. Only have 36000 miles on it. Only makes the noise in slow turns for either direction. Wish there was a known inexpensive fix for this.

http://www.gm-trucks.com/forums/topic/79774-groan-from-steering-column-when-turning/page-2

FYI:

After year 3 and after warranty expired, I also had to replace the Evap Vent with a $500 Evap Vent Kit after it being replaced after year 2 under warranty. Also had to replace the Alternator for just under $500. Not too happy with this GM product. Was hoping they had gotten their act together by now. May have to try a Tundra next time.