Hyundai says that some 2010 Santa Fe SUVs and 2011 Sonata sedans (both with 2.4-liter engines) may turn on the Check Engine light and log trouble code P0128 (coolant temperature below thermostat regulating temperature) in the PCM.
According to the carmaker, the trouble is most likely to occur when the blower motor and heater control settings are set on high, and is caused by design flaws in the thermostat housing and the thermostat itself. Replacing the 'stat housing, thermostat and gasket with revised parts (25630-2G710, 25500-23010 and 25633-2G000, respectively) should turn off the light and eliminate the code.
When installing the new thermostat, it's important to make sure the jiggle valve is positioned at the top and the notch on the thermostat fits into the groove in the housing. When properly positioned, the thermostat should be centered in the housing with no visible gaps around the housing edges.
"Factory Fixes" is written by Jim DePalma, a 30-year veteran of the auto repair business who has served stints as a service manager, parts manager and ASE-certified technician. His column provides vehicle manufacturers' authentic factory technical service bulletins (TSBs) that have been condensed for easier reading. Mr. DePalma advises that techs always check with a dealer or repair information system for the latest revisions before starting to work on a vehicle. He can be reached via e-mail at [email protected].