hypervish

Hey all,

So my 02' ES300 threw a P0128 at the end of last month at 230,763. I reset the light, and it came back today at 231,6XX.

Code states -- Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

This leads me to believe it's the thermostat. I hooked up my iPhone to the OBDII and went for a drive and watched the coolant temperature. It took nearly 10 minutes of driving to get to 170ish degrees. Afterwards, drove for another 10 minutes and while sitting at the Taco Bell drive through temp was hovering around 190 degrees. I tried to log the data, but for some reason it didn't save.

Does this sound like a thermostat? Or should I be looking at the coolant temperature sensor?

Thermostat is easy enough to replace, seems pretty similar to my Sienna. Thinking about just throwing an OEM thermostat at it. But would rather be sure it's the problem.

Oro

10 minutes to get to 170F sounds totally like a thermostat stuck open.

Having checked aftermarket and OE thermostats, I would suggest definitely go OE/OEM. The aftermarket one I bought was clearly inferior. Last year I put my stock/original one back in (I had it apart for other maintenance, not failed thermostat and was going it as prevantative) and it's still going at ~250k. Next time I do coolant I will put in an OE one in and not anything else.

CharBaby

I agree with Oro! Most likely the T-Stat and do indeed stay with the OE Stat!

hypervish

Ok, thanks fellas!

Yep, definitely only OE; thermostat and gasket come out to $30, well worth it IMO.

blucobra03

hypervish, did you change out the thermostat and has your P0128 code now gone away ? I just did a post yesterday looking for assistance with this same exact issue in my 2003 ES300. I have 149K miles on it. I tried a search before posting but used thermostat as my criteria and never saw your post until another member was good enough to provide the link. Great members you have on this site. Thanks all !

hypervish

Sorry for not posting an update.

Yes, I replaced the thermostat at 232,672 miles, and the code has not returned. It now has north of 235,000 miles, so I think it's safe to say the thermostat has fixed it.

Toyota Part Numbers are as follows:
Thermostat: # 90916-A3003
Gasket: # 16325-62010

I suggest buying it from eBay if you are not in a rush, I got both thermostat and gasket for $30 shipped to my door. And, OEM parts only as Oro suggested above!