P0128 OBD-II Trouble Code
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
What does that mean?
This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125
In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.
You will likely not notice any drivability problems other than the MIL illumination.
A code P0128 may mean that one or more of the following has happened:
- Low engine coolant level
- Leaking or stuck open thermostat
- Faulty cooling fan (running too much)
- Faulty coolant temperature (ECT) sensor
- Faulty intake air temperature (IAT) sensor
Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:
- Verify coolant strength & level
- Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
- Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
- Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
- If the above items check out good, replace the thermostat
- If Nissan vehicle, check for Technical Service Bulletins (TSBs), as the ECM may need to be reprogrammed to correct the P0128 code
We value your feedback, please complete a very short survey to tell us your thoughts on this DTC article.
Related P0128 DTC Discussions
- 2000 grand prix p1404, p0404, p0440, p0300, p0128
2000 grand prix gtp 3.8 Bought car recently for work vehicle, ran great check engine light was on though. One morning leaving for work car was idling terribly and upon entering freeway check engine light began flashing. (looked that up was cat failure) Showing multiple codes:p1404,po404,p0440,p0300...
- 2005 CHEVY IMPALA P1811 P0128
156K 3800 ENGINE...
- P0128 code came up and temp gage not working 2001 Olds Alero
I have a 2001 Old Alero with a 3400 motor in it. The code came up P0128. The check engine light came on and Temp gage wasn't working. I replaced the coolant temp sensor. The light is still on and Temp gage still not working, What else can I check. The temp gage does not move at all. Any suggestions...
- Codes P0100 & P0128 - Chevy Equinox 2006 LT
Hello, 2006 Chevy Equinox LT, ~108000 Miles Recent work done on the car was the oil changed (just last week actually), air filter changed (same time as oil change). The oil was changed to Mobil 1 Full Synthetic 10W-30 I was wondering if I can get some help with this? I don't know where I should sta...
- Code P0128 2002 Oldsmobile thermostat
Where the heck is the thermostat on a 2002 olds aurora 3.5L V6 and whats involved in replacing it. Can a D.I.Y. person do the job or does it have to go to a garage or dealer? Auto Parts stores have no listing for a thermostat for this vehicle. Have been told that the reason for the P0128 code is ...
Need more help with a p0128 code?
If you still need help regarding the P0128 trouble code, please post your question in our FREE car repair forums.
NOTE: This information is presented for information purposes only. It is not intended as repair advice and we are not responsible for any actions you take on any vehicle. All information on this site is copyright protected. If you want to share this article or information with others, please link to this page, don't copy and paste it elsewhere.