Diagnostic Aids
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 Pontiac Grand Prix, 2002 Pontiac Bonneville, 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, and 2002 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0125 is designed to detect a skewed ECT sensor.
If a DTC P0125 and a P0128 are set a faulty thermostat may be the cause, M/T.