Engine Controls - Self-Diagnostics: Introduction: Notes

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 article in GENERAL INFORMATION before disconnecting battery.

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

The engine used in this vehicle has controls to reduce exhaust emissions while maintaining good driveability and fuel economy. An Engine Control Module (ECM) is the heart of this control system. Fig 1 has a list of sensors and inputs the ECM uses to get information about engine operation and the various systems it controls. For details for basic operation, see THEORY & OPERATION article, for diagnosis and service, see SYSTEM & COMPONENT TESTING article.

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

Both the ECM and BCM have the capability to diagnose faults with the various inputs and systems they control. When the ECM recognizes a problem, it turns on the "Service Engine Soon" telltale lamp on the instrument panel to alert the driver that a malfunction has occurred. The ECM will also send a message to the BCM to turn ON the "Service Car" message on the Driver Information Center (DIC).

Fig 1: Identifying ECM Operating Conditions Sensed & Systems Controlled

Courtesy of GENERAL MOTORS CORP.