Most techs consider code P0128 a bad thermostat code. Basically, the thermostat is stuck open and the PCM starts a timer when it is started and then it watches the coolant temperature and compares it to a table of what it thinks the coolant temperature should be for the engine load and time run. It sets the code if the coolant temperature doesn't match the table.
The thermostat on that engine isn't that bad to swap. You start by draining the coolant level below the housing, then remove the air intake housing, remove the clamp, slide the hose off. Now remove the housing and clean the surfaces. Swap out the thermostat. The housing bolts get tightened to 18 ft lb. Refill the cooling system. Open the bleed screw and let the air bleed out until the system is full. Now start the engine and let it warm up while watching the coolant level. I like to run the engine until it's up to temperature and then add coolant in the overflow and let the system cool and draw in coolant. Top up the reservoir as needed.
Dec 8, 2022 at 5:46 PM
