I hammered the truck a little going down the highway with Hypertech Max Energy on stage 3 then put back to stage 1 for towing and found a DTC PO0128...thermostat..........any idea? I reset and went on.
The ECM is calculating an expected Coolant Temp given the fuel that has been burned and the time that it has been burning it. If the coolant temp does not meet or exceed the calculated temp, you get the code.
Check for proper coolant level.
Perform Coolant System Leak Test.
Inspect fan for proper operation.
Inspect the fan belt to ensure it is in good operating condition?
Remove thermostats and verify proper operation. Bring to boil in a pot of water and see what temps they open and close at. Start opening ~ 160 Fully open at ~ 180 Degrees F roughly.
Could also be a bad ECT Sensor. You can do a resistance check at various temps. At 0 degrees F Res = 9420 ohms At 50 degrees F Res = 973 ohms at 100 degrees F Res = 177 ohms, at 150 degrees F Res = 47 ohms.
This condition could also be caused by air in the coolant system. That could possibly be an indicator of a bad head gasket. After shutting the warmed engine off, and letting it set for several hours, check the upper Rad hose to see if it is hard. If it is hard, you probably should test for a headgasket failure.
Did you try running it at a different tune to see if you still get the code? If all the above is within Spec, then the tuner could be causing the ECM to give you a bad calculation.
Maybe not, I usally baby my truck but a guy at work who has a Ford gas truck and has been talking smack. I should have let it warmed up completely, had it it idling a couple of minutes...but I just had to show him my tailgate at a distance.Was the truck fully warmed up before getting on it?