Rick's Free Auto Repair Advice

Hyundai code P0128

Fix Hyundai P0128 coolant thermostat trouble code

Hyundai has issued a service bulletin #11-FL-003 to address a Hyundai code P0128 in the vehicles listed below. The Hyundai code P0128

2011MY SONATA 2.4L
2010MY SANTA FE 2.4L

The service bulletin applies to vehicles with the 2.4L engine that store a P0128 coolant thermostat code when the heater/defroster is used at maximum blower speed and high heat setting.

To correct the problem, replace the thermostat, cooling inlet, and gasket with revised parts.

1. Drain the engine coolant until the level is just below the thermostat.
2. Remove the radiator lower hose
3. Remove thermostat, gasket, and water inlet fitting.
4. Install the new parts in reverse order of removal.
Tightening torque: 7.8 ~ 11.8N.m (0.8 ~ 1.2kgf.m, 5.8 ~ 8.7lb-ft)

NOTE: The new thermostat has a jiggle pin to bleed air out of the cylinder head. The thermostat must be installed so the jiggle pin is placed at the top and so the notch in the thermostat fits into the groove of the house.

5. Remove, flush, and refill the engine coolant.


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Posted on by Rick Muscoplat


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