GM Service Manual Online
For 1990-2009 cars only

The electronic PRNDL display indicates the transaxle gear position to the driver. The PRNDL control module receives gear position data via the UART serial data line from the powertrain control module (PCM). Refer to Instrument Panel Cluster Microprocessor. The PCM reads the transaxle position from the transaxle range switch.

The PRNDL control module receives light dimming information over the UART serial data line. This causes the PRNDL display to dim to the present control level with the park lights or the headlights ON.