Engine Controls - DTC P0128

SOURCE: Kia PitStop

TITLE: DTC P0128

APPLIES TO: 01 Optima

SERVICE TIP:

Under certain cold weather operating conditions 2001MY 4-cylinder Optima may set a DTC P0128 (thermostat malfunction), even though no drivability concerns exist, the thermostat is operating properly, and a normal operating temperature is reached without noticeable delay.

2001MY 4-cylinder Optima P0128 logic uses a temperature threshold of 82°C (179.6°F). This threshold must be reached within a certain time after start-up, or the ECM will consider the thermostat inoperative / stuck open. Note that time after start-up in this case is actually a function of mass airflow. For more details and additional parameters, refer to the Hi Scan Pro; with the P0128 DTC displayed on screen, then hit the "help" button and select "tips".

For 2002MY 4-cylinder Optima, the DTC P0128 logic temperature threshold was reduced to 75°C (167°F) to reduce incidence of P0128 code. It is suspected that in certain ambient temperature operating conditions, the higher threshold in 2001 MY causes the DTC to be stored even though the thermostat did not fail.

KMA is aware of this condition and is currently investigating possible countermeasures to correct incidence of P0128 codes occurring in certain cold weather operating conditions.