Reset code P0128 after changing thermostat

RGG · Post by **RGG** » 25 Oct 2010, 15:30

Check engine light came on and went to Auto Zone and their reader showed
a code P0128. Coolant sensor was replaced 7000 miles ago as was the thermostat. I decided to just replace thermostat with a Fail-Safe one. Hope more expensive really means better. Will the P 0128 code clear itself or does it have to be reset ?

Post by **FlyingVolvo** » 25 Oct 2010, 15:32

A thermostat will never trigger a code (unless if fails closed and blows up your engine...).

When you replaced the coolant temp sensor... did you use a Genuine Volvo one? Anything other than that will likely cause trouble. They're more expensive, but they are the only thing that will work well. I replaced my original one a couple months ago after 10 years and 145,000 miles... and it wasn't even bad yet.

claytorwake · Post by **claytorwake** » 19 Mar 2011, 05:53

Had a P0128 code on my daughter's '04 S40 1.9 turbo. Temp gauge was reading normal after the engine had warmed up but it was also taking longer than normal to get heat. Based on that it appeared the thermostat was not closing completely so I changed just the thermostat and gasket and not the temp sensor. Flushed out the cooling system and filled with fresh antifreeze while I was at it. Code has not come back and she has heat very quickly. Used a Super Stant thermostat. Sprayed the 2 torx bolts for the thermostat housing with PB Blaster and they came out easily. Also used anti-sieze when I put them back. Read where these are easy to break.

Post by **jimmy57** » 19 Mar 2011, 09:04

"ecbsykes"]A thermostat will never trigger a code (unless if fails closed and blows up your engine...)."

Not true of any Volvo starting with Motronic 4.4 engine management models.
The ECM expects a temp rise that meets or exceeds a certain rate and sets a code when it fails to do this.
SO stuck open thermostats are detected and set codes.