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.
Symptoms
You will likely not notice any drivability problems other than the
MIL
illumination.
Causes
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
Possible Solutions
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
Other ECT sensor and circuit related DTCs:
P0115,
P0116,
P0117,
P0118, P0119,
P0125
I forgot to mention that the thermostat on the instrument panel is always showing low, never goes up. Would this have any impact on your recommendation?
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