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roadsidejerry, auto mechanic
Category: Chevy
Satisfied Customers: 2948
Experience:  Auto Mechanic 39 years, 30 with NYPD Fleet Service Division
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Chevrolet Malibu Maxx LS: P0128..pinpoint..theenginecoolant

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Original Question on justanswer: Chevrolet Malibu Maxx LS giving ODBII code P0128. I know what the code is, but not sure how to pinpoint the actual problem.

Origianl Answer on justanswer: The code is basically saying that the engine coolant is not getting up to temp. If the gauge says the temp is up to operating temp then the most likely suspect would be the ECT sensor not reading correctly. If the temp gauge reads low (180 or below) then the thermostat is the probable cause. Hope this helps.

Follow-up Question: I'm not sure what the temperatures are on the gauge. The needle always seems to make it's way to the middle of the gauge once the car is warmed up and it stays there. It never seems to go up or down until the car is shut off.The cooling fans seem to be operating correctly (ex. they come on with the A/C and go off shortly after shutting the A/C off).
The code came back a 3rd time, but it took over a month.
The code has now been coming back on the day after resetting it.
HelloCustomer you would need to find out if the coolant is getting to 195 degrees. A scan tool that reads live data would be needed. You could also use a thermometer made for checking cooling systems,it is designed to check the coolant temperature.We know have an infra red temperature gun that makes this testing easier.Most common cause of this condition is the thermostat. If the sensor was defective,this would be tested by comparing the actual coolant temperature with the reading on the scan tool,they should be the close to the same,within a few degrees. If not the sensor and wiring would need to be tested. If it was my car,I would replace the thermostat as a first step.
Customer: replied 8 years ago.
Reply to roadsidejerry's Post: I should have mentioned that the coolant temperature was checked at the dealer last week and they said it was normal. Although I didn't ask them what the temp was.
I believe thermostats are not that expensive, but are they difficult to install on this car? Should the dealer to the install?

Hi,the thermostat is not to expensive to replace,I do like to use the dealer parts when possible. I would like to know what the temperature was before just replacing parts. If they say it read 195 there is no reason for the code P0128 to come up,unless you have an intermittent problem.A reading of the freeze frame data ,when trouble code caused the light to come on would be one of the things to find out. It would show the coolant temperature when the light came on.The idea of testing is to compare the coolant sensor reading with the actual coolant temperature. I will send you the testing procedure from the service information,you will see what it involves.I would ask the dealer to diagnose and tell you what they find for the reason the code is being set.


roadsidejerry and 5 other Chevy Specialists are ready to help you
Thanks for the accept and positive feedback,let me know what you find. You can post back to this question at any time. It will not cost you again. I hope it turns out to be a simple fix,Jerry.