Chrysler thermostat rationality. That’s a technical description for DTC P0128. This involves a few Chrysler models equipped with the 3.5L engine. specifically 2009-2010 Challenger, 2008-2010 300, Charger and Magnum.
Some customers may complain of a MIL illumination. During diagnosis, DTC P0128 may be stored, indicating that “thermostat rationality has been set.” This condition may be caused by the block retaining feature for the thermostat not holding the thermostat in place. This causes the thermostat to tip into the engine block opening, allowing coolant to pass through without going through the thermostat. With the thermostat out of position, the system will set this DTC.
This bulletin involves installing a shim onto the thermostat for vehicles that have not experienced the MIL illumination, and replacing the thermostat housing for those vehicles that have set this code. The new thermostat housing kit includes the new shim.
Using a scan tool with the appropriate diagnostic procedures available in TechCONNECT, verify that all engine and transmission systems are functioning as designed. If DTCs are present other than P0128, record them and repair as necessary before proceeding.
Remove the thermostat housing following the detailed procedures available in DealerCONNECT/TechCONNECT group 7 – Cooling > Engine > Thermostat removal procedure.
Install the new shim over the thermostat (No. 1 in the figure shown here). NOTE: The shim may present a tight fit over the thermostat.
Install the thermostat housing following the procedures listed in TechCONNECT.
Fill the cooling system and bleed, according to the procedures listed in TechCONNECT or the service manual.
ITEM PART NUMBER
Thermostat housing kit (thermostat, housing and shim)……….68148113AA