2.0L LSJ Engine SES Lamp Illuminated with DTC P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature Set (Reprogram PCM)

This bulletin is being revised to add the 2004 model year. Please discard Corporate Bulletin Number 05-06-04-038C (Section 06 - Engine).

Some customers may comment that the Service Engine Soon (SES) lamp is illuminated. Diagnostic Trouble Code (DTC) P0128 "Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature" may be set.

Under certain ambient engine temperature conditions, the thermostatically controlled engine coolant temperature may not reach the calibrated threshold in the allotted time frame that is programmed in the PCM.

Follow the steps outlined in the " Service Procedure" section of this bulletin to repair a false DTC P0128.

Verify operation of the thermostat and cooling system. Refer to "DTC P0128" diagnostic in published Service Information. Before replacing the engine coolant thermostat and/or updating PCM calibration for repairing a false DTC P0128. Perform the following service procedures:

1. Observe the coolant temperature within the P0128 Freeze Frame.

•	If the engine coolant temperature is greater than 70.25°C (158.25°F) with DTC P0128, the PCM needs the updated calibration. Do not replace the engine coolant thermostat.

•	If the engine coolant temperature is less than 70.25°C (158.25°F) with DTC P0128, replace only the engine coolant thermostat.

Important: Chevrolet Dealers: The PCM calibration is available to dealerships as part of TIS2000 incremental satellite update version 4.0, which was broadcast to dealers in April, 2006 or later. For the dealerships that use CDs, they were mailed out April, 2006 or later.

Important: Saturn Retailers: Before installing the new PCM calibration, make sure the Saturn Service Stall (SSS) version is TIS 4.0 2006 or later.

Important: While the ignition is OFF, apply the parking brake to disable the daytime running lights (DRLs) prior to starting reprogramming procedures.

Important: Technician must select the "Reprogram" option in order to reprogram the PCM.

2. Reprogram the PCM with the latest calibration. This calibration, or any that follow, is designed to address this DTC P0128 concern. Refer to "Service Programming System (SPS)" in SI for reprogramming procedures. As always, make sure your Tech 2® is updated with the latest software version.

If PCM Programming Was Performed:

For vehicles repaired under the 8-year/80,000 mile (130,000 km) emission controller warranty, use:

If Thermostat Was Replaced:

For vehicles repaired under warranty, use: