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:

• The EBCM has disabled the PCS/TCS due to a DTC.
• The instrument cluster bulb check. When the ignition switch is turned to ON, the PCS/TCS indicators will turn on for approximately 3 seconds and then turn OFF.
  Fig 1: Precision Control System (PCS) Indicator Always On

  Courtesy of GENERAL MOTORS CORP.