Circuit Description

The PCS On indicator is controlled by the instrument cluster via class 2 serial data messages from the EBCM. When the instrument cluster sees the PCS signal input grounded, it sends a class 2 message to the EBCM that tells the EBCM that the PCS is malfunctioning. The EBCM then disables PCS and TCS and sends a message to the instrument cluster to turn the PCS and TCS indicators ON. Each time the ignition is cycled from OFF to ON, the PCS is enabled:

The following conditions will cause the PCS/TCS indicators to illuminate:

• No signal received from the EBCM.
• The instrument cluster PCS indicator bulb is blown.
• Harness connector malfunctioned.
  Fig 1: Precision Control System (PCS) Indicator Inoperative

  Courtesy of GENERAL MOTORS CORP.