Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The diagnostic procedure used for DTC U1500 in OnStar® systems with single module generations of OnStar® differ greatly from previous generations with 2 modules. While these older generations denoted a failure of the 3-wire bus between the modules by setting a U1500, single module OnStar® systems use this DTC to denote an internal module failure. The determination of whether a one or 2-module generation of OnStar® is used should be confirmed. Refer to OnStar Description and Operation .
This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the VCIM.
If this DTC is retrieved as both a current and history DTC, replace the VCIM.

DTC U1500

Step	Action	Yes	No
1	Did you perform the Cellular Communication Diagnostic System Check?	Go to Step 2	Go to Diagnostic System Check - Cellular Communication
2	Install a scan tool. Turn ON the ignition, with the engine OFF. Retrieve DTCs from the vehicle communication interface module (VCIM). Is the DTC retrieved as a current DTC?	Go to Step 3	Go to Diagnostic Aids
3	IMPORTANT: Perform the OnStar® setup procedure. Replace the VCIM. Refer to Communication Interface Module Replacement (TrailBlazer, Envoy, Bravada) Communication Interface Module Replacement (TrailBlazer EXT, Envoy XL) .Did you complete the replacement?	Go to Step 4	-
4	Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text. Does the DTC reset?	Go to Step 2	System OK