P0128 Diagnosis

P0128 Diagnosis

 

MY P0128 Video is below this Article

 

 

The P0128 Code reads as "Thermostat Below Regulating Threshold". The P0128 Code is actually really simple to diagnose. It is usually a Thermostat sticking open that will cause the issue, however we need to also check the Coolant Temp Sensor (ECT, CTS) also before we condeme the Thermostat.

 

Let me save some of you some time. Like i said this is usually always a Thermostat stuck open causing this. If you dont like to waste alot of time and you have not had a new thermostat in a while, just go ahead and do the Thermostat. Thermostats are Cheap! ($10 with a seal/gasket) Otherwise you can read more into my blog on how i describe the operation of the thermostat and in a little more detail the reasoning behind this code being set and some things to check with your temp sensor.

 

The Coolant System is designed to block off the flow of coolant thru the radiator until the car has reached a predetermined temperature (This is what the Temp rating on your Thermostat means). When the car does not reach this temperature in a set amount of time and the car determines this by use of other sensors that the car has been running long enought that it should have reached proper temperature, it will Illuminate Your Check Engine Light and Set Trouble Code P0128. It will do this not the 1st time is sees the problem, but the 2nd time the car is started and driven and it sees it again. This is called 2 Trip Logic.

 

Watch your temp guage on your dash, is it taking longer than usual to reach the middle of the guage? The best way to check the Coolant temp sensor is to have a Scan tool Device that will read Data, and make sure the Coolant temp is moving. If the Coolant Sensor had failed all the way, it usually resorts to a reading of -40 Degrees(Yes thats Negative 40 Degrees) and will set its own code (P0118) and the P0128 Code will not illuminate with a Coolant Temp of -40 Degrees because it knows already its the Coolant Sensor. Is the guage even going all the way to the middle? Usually with this code the guage will not even make it all the way to the middle. You can CAREFULLY touch your raditor hoses very quickly to feel if they are up to temp or not, if they still feel cool after the car has been running more than 5-10 minutes you can almost bet your Thermostat is sticking open. This might not seem like a big deal to most people. "Well at least its not stuck closed, and causing it to overheat"! But guess what ITS WASTING YOUR GAS!! For every second the car has not reached Proper Operating temperature Your Computer is demanding that extra fuel be added to the mix to help the car warm up faster! Not to mention your oil does not come up to temperature like its accustomed to so it will overtime begin to "Sludge"...think of that word..."Sludge"...it just doesnt sound good and we know its not good. So dont let this go too long!!

 

Questions? Email me at MyPeoplesGarage@gmail.com

 

My P0128 Diagnosis Video Below!!!