Engine Controls - Self-Diagnostics: Introduction: Notes

WARNING: Vehicles are equipped with air bag supplemental restraint system. Before attempting any repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in AIR BAGS -- ALLANTE article.

CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES -- GENERAL MOTORS article in GENERAL INFORMATION before disconnecting battery.

CAUTION: Power should never be removed or applied to PCM or BCM with ignition switch turned to ON position. Before removing or connecting battery cables, fuses, or PCM/BCM connectors, always turn ignition switch to OFF position to prevent damage to modules.

The powertrain used in this vehicle consists of a 4.6L dual overhead cam engine mated to a 4T80-E electronically controlled transaxle. It has controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The Powertrain Control Module (PCM) is the heart of this control system. Fig 1 has a list of sensors and inputs the PCM uses to control engine components, transaxle and other systems.

In addition to the PCM, this vehicle contains a Body Computer Module (BCM) which is used to control various vehicle functions based on sensors and switch inputs. Information covering basic operation, diagnosis, and service of the BCM is covered in BODY COMPUTER MODULE -- ALLANTE article.

The PCM has the capability to diagnose faults in the sensors, input switches, components and systems it controls. When the PCM recognizes a problem, it may turn on the "SERVICE ENGINE SOON" MIL on the instrument panel or send a message to the BCM to turn on the "SERVICE VEHICLE SOON" message on the Driver Information Center (DIC) to alert the driver that a malfunction has occurred.

Fig 1: Identifying Powertrain Control System Inputs & Outputs

Courtesy of GENERAL MOTORS CORP.