Trouble Code P0128

[CSCS Trainer]

got a CEL this afternoon and plugged in the Predator to see what it was and it displayed code P0128 - Coolant Thermostat. "Coolant Temp below thermostat regulating temperature."

I do have a 180* t-stat, but that has been in for about 3 months. Any idea of the problem? Temperature readout on the EVIC was 208* at the time of the code. Thanks.

[Rev Scorpion]

It could one of 2 things...

Most likely is a thermostat that is opening too soon.

could also be an ECT that is failing and reporting false numbers.

connect the predator to a cold engine and start the car.
monitor the ECT values as the engine warms up.

Watch for the temp to rise normally then suddenly drop 20 - 100* then jump back up.
If it does you are likely dealing with a bad ECT sensor.

Otherwise...
watch the temp for when the t-stat opens. If it opens much before 180 you might need to replace the t-stat.
I have a 180 in mine and have had no problems....

[TheSurgeon]

Our other car shoots the same code and the chk engine light turns on,I think the thermostat stays open. then a day later it turns back off, need to get that fixed before the summer.

[karh4ck3r]

It might just go away when it gets warm.

[CSCS Trainer]

Thanks for the info Rev. I haven't really played around with the Predator much. So when I connect it, what settings am I going to go into to watch the ECT?

[MangoInTX]

The setting to monitor on my O6 EVIC is "Eng. Temp= xxx" (<= xxx = temperature in degrees fahrenheit).

From a cold start the temperature steadily rises, once it gets at or above 180 degrees (this also depends on the make/model of T-Stat) the T-Stat will open and you will see that the temperature stops rising, it may dip slightly, this indicates the T-Stat opening temperature according to EVIC. I run a Stant 180 T-Stat and it opens at 185, when driving it settles in at 186-188.

With your Predator you will select “Modify tune” and then select the "Cooling Fans" option. You will see the following three groups of settings for the fans. Tweak these setting up or down (up in your case) to dial in your t-stat.

Fan control:

AC off high MPH high speed fan on temp
AC off high MPH low speed fan on temp
AC off high MPH medium speed fan on temp

AC off low MPH high speed fan on temp
AC off low MPH low speed fan on temp
AC off low MPH medium speed fan on temp

AC on high speed fan on temp
AC on medium speed fan on temp
AC on low speed fan on temp

As others indicated the T-Stat may be faulty and opening too soon. You will know if that is the case while you monitor EVIC.

Take your time and good luck dialing her in!

[Rev Scorpion]

Thanks for the info Rev. I haven't really played around with the Predator much. So when I connect it, what settings am I going to go into to watch the ECT?

I am not 100% sure here since I use a scan tool and not the Predator, but I think the ECT value is simply marked "ECT". At the very least it will be something very similar.

While you can monitor it on the EVIC, I am not sure exactly how precise that is (update rate, etc.), so for this I would prefer the use of the Predator.

I have read dozens of posts about the cooler t-stats setting codes at times, so I am as close to 100% sure as I can be that the issue is just a T-stat, but better safe than sorry.



What Mango said is true....
Once you get the issue resolved, go in a tweak your fan settings.
When I did mine, I dropped all of them about 10*. Search on the "Z" and there is a thread about fan settings.