So sorry to post a V40 question in the S40, but it seems that is where people look.

I have a 2001 v40 1.9T with 76k that has a recurring ECM fault code P0128. From the SAE book I have it says that "the PCM has determined that the input from the coolant temperature sensor indicates a temprature value that is below the thermostat regulating temperature." OK - So my (mis)logic tells me that could be one of two things. That the sensor is bad (or its wiring/plugs/etc) or the thermostat is sticking open. Since the fault comes up when it is cooler more then warmer (generally it will come un 3-4 days after being reset) I tend to believe it is the thermostat. Since they are only $8, as opposed to $70 for the sensor, I figure that is the place to start. The only odd thing is, the dashboard temperature guage is pretty much where it has been for the last 4 years.

So I'd like to know if anyone has a table of temperature sensor values that they would like to share with me (hint Tech, please!) so I don't have to buy something I don't need to and can start looking elsewhere for the problem.

Peter

Sorry I don't have a table for you to look at.There was 2 problems with what you are complaining about half of the time the thermostat is broke and the other half is the sensor.The thermostat has a gasket as part of the thermostat like an o-ring on the outside of the thermostat.You can remove the housing usually whithout causing any damage and can reuse.You will know right away if it is broke once you open it.

We shall see. The thermostat still had a decent spring, but it was a little sticky on the shaft. I replaced it, and pulled the sensor out. It seems difficult for me to believe the sensor could be bad unless the casing failed and allowed the bitmetallic thermistor to be contaminated with coolant or air. It gives a value, and that seems like it is either working or not. So it is back in, and yes the gasket was fine to reuse, thats good because they didn't give me one (there computer said to used sealant !&^%#!).

ORIGINAL: mercury320

So it is back in, and yes the gasket was fine to reuse, thats good because they didn't give me one (there computer said to used sealant !&^%#!).


I guess there computers need to be updated.Those sensors are weird.In the 5 years I have been with Volvo I have seen many of those sensors go bad.They have pretty much been using the same style sensor since 1993.