Engine Controls - Tests W/Codes - Pcm/BCM: Operation

Inputs from major components, sensors and switches are used in calculations by BCM and combined with program instructions within system memory. This provides accurate control over all subsystems involved. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and back-up functions may be provided.

The BCM controls subsystems through direct outputs or through data transmitted along the serial data line to one of the other major components. The process of receiving, storing, testing and controlling information is continuous. The data communication also gives the BCM control over the ECM's, IPC's, and DERM's self-diagnostic capabilities. Between the BCM and the other major components of the computer system, a data line communication process has been incorporated. This allows devices to share information and thereby provide for additional control capability.

In order to access and control the BCM self-diagnostic features, 2 electronic components are used, the Instrument Panel Cluster (IPC) and the Electronic Climate Control Panel (ECCP). See Figure . The SERVICE MODE for diagnostic information incorporates odometer/trip odometer as Driver Information Center (DIC) display. When a malfunction is sensed by the BCM, the Service Engine Soon (SES) light will illuminate on IPC and stay on (with engine running) until code is cleared from BCM.

When the SERVICE MODE is entered, various BCM, ECM or IPC faults can be displayed. In addition to the parameters, fault codes, inputs and outputs, and other features such as override commands, snapshot, display VIN and code clearing capabilities can be accessed and displayed when commanded through the ECCP.

Certain system malfunctions cause computer controlled diagnostic messages and/or telltales to appear, indicating that service is required. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and the BCM provides certain back-up functions known as "failsoft". A typical failsoft action would be the substitution of a fixed input value when a sensor is detected to be open or shorted.

The ECCP becomes the controller by which to enter and access self-diagnostics. By pressing the appropriate buttons on the ECCP, data messages can be sent to the BCM, requesting specific diagnostic features. This communication process allows BCM to transfer any of its available diagnostic information to the instrument panel DIC display during SERVICE MODE operation. When in override mode of BCM diagnostics, information is displayed at the ECCP temperature LED display. Below is a list of computer controlled subsystems.

• Alternator/Starter System
• Chime
• Climate Control
• Courtesy Lights
• Cruise Control
• Dimming (Lighting)
• Driver Diagnostics
• ECM Subsystems
• E & C Data
• Gauges
• Illuminated Entry
• Instrument Panel Displays
• Radio
• Self-Diagnostics System
• Supplemental Inflatable Restraint (SIR) System
• Twilight Sentinel