Desired Engine Coolant Temperature

[chris209a]

Hi, getting a P0128 code thrown on my 02 8.1 Suburban and interested in where the desired ECT is stored and if it can be changed. Changed the thermostat to a 180 degree a couple of years ago and this code only appears in the winter months. Changed the thermostat as I read that a 180 reduced oil consumption which it certainly has.

[nonnieselman]

It is probably something deep in the programming that we cant get to.. If it were me, id just disable that code and keep on riding.

[joecar]

P0128 indicates that coolant temperature isnot reaching sufficient temperature within time window expected by PCM.

Did it just start showing up recently, or was it always there dince you changed tbe thermostat...?

Check the following:
- coolant level (low).
- thermostat (stuck open).
- failed ECT sensor (reporting low or constant value).
- fan runs always (failed relay or short circuit).

[joecar]

...this code only appears in the winter months.

If ECT sensor is ok, then try blocking off air flow to part of the radiator, and observe ECT to see what it does.

[chris209a]

It is probably something deep in the programming that we cant get to.. If it were me, id just disable that code and keep on riding.

Just prefer to disable as a last resort and keep codes to show if something changes

[chris209a]

Just started in the cooler weather we are having now, changed the thermostat a couple of years ago, coolant level is fine, temp gauge responds as normal and engine warmup doesn't seem to take any longer. The fan is mechanical so no change, does the same ECT sender drive the gauge?

Will try a new ECT sender first and see if that makes any difference.

[chris209a]

Will try that thanks, just keep thinking there must be a time and temperature setting somewhere to check against to either set the code or not. It must be changed for other GM engines as a full aluminum engine would heat up quicker than the 8.1 lump of cast iron.

[Highlander]

There is a temp setting for that code.

[chris209a]

Great, any idea where it might be?

[joecar]

Try looking in the Engine Diagnostics segment.