'04 PT error P0128 won't go away!!!

Ok, here's what happened. Last week, hot day bubbling overflow tank,
very high engine temp -- replaced thermostat. Topped off coolant with
50/50 anti-freeze. Problem solved.

This week, check engine light comes on, error code P0128 - thermostat
rationality(?) problem. Saw that the overflow tank was low, topped it
off to the fill mark. OK, cleared the error code by disconnecting the
battery. Everything's fine then tonight, engine light comes on again,
P0128 error code again! Levels are fine, car runs a little cooler then
normal I guess, but it was pretty cool today.

No water in the oil. Tested thermostat - works fine. Upper hose is
ok not rock hard.

ANY IDEAS?

JaKe

 

JaKe,

Any obvious coolant leakage other than at the reservoir overflow tube? Does
your cooling fan come on and run when the coolant reaches operating
temperature? (You do not say, but I suspect not).

Bob

 

Yes, the fan is working fine. I believe it's a bad coolant sensor.
I'm going to probably replace it.

 

I'm not familiar with the PT and do not know if it uses one or two coolant
temperature sensors (some cars use one for the fan circuit and another for
the temp gauge). If it uses one for both and the cooling fan turns on at
the right time/gauge temperature, then it would seem to be working OK. In
any event, replacing it shouldn't be difficult or hurt since it would be a
cheap fix.

Are you sure that both fans turn on and run (engine cooling and A/C fan)
when appropriate? If the fans are OK and assuming you got the new
thermostat in correctly, then another thought here is that it could be a
bad coolant pressure cap.

Good luck

Bob

Yes, the fan is working fine. I believe it's a bad coolant sensor.
I'm going to probably replace it.