Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.

A DTC P0128 is designed to detect a faulty thermostat.
Excessive coolant flow through the by-pass hose to the throttle body may cause this DTC to set.
A skewed ECT sensor may cause a P0128 to set.
A skewed IAT sensor may cause this DTC to set.