On Board Diagnosis Logic

WARNING: This page is about a different car, the 2005 Infiniti QX56. However, it is still accessible from the selected car via links, so may be relevant.

Engine coolant temperature has not risen enough to open the thermostat even though the engine has run long enough.

This is due to a leak in the seal or the thermostat stuck open.

Fig 1: DTC P0128 Thermostat Function - On Board Diagnosis Logic

Courtesy of NISSAN MOTOR CO., U.S.A.