Diagnostic Aids

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

Check for the following conditions:

A faulty thermostat that stays open slightly can cause DTC P0128 to set in cold weather when vehicle is started and allowed to sit while warming up. Replace any suspect thermostat.
An incorrect thermostat can cause engine to warm up slowly. Replace any thermostat that does not meet OEM specifications.
Use Temperature vs. Resistance table to evaluate possibility of a shifted ECT sensor. A shifted sensor could result in DTC P0128. See TEMPERATURE VS. RESISTANCE table.
Check for proper operation of engine cooling system, including correct coolant level.
Check for a faulty electrical connection to PCM.

If DTC P0128 cannot be duplicated, information included in freeze frame data can be useful in determining vehicle operating conditions when DTC was first set.