Engine Performance: System: 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.

To properly diagnose and repair this vehicle, follow testing procedure in PFI SYSTEM CHECK . If no DTCs are present and a driveability condition exists, proceed to 1989 TROUBLE SHOOTING - NO CODES -- ALLANTE article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

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. Details for basic operation, see THEORY & OPERATION article, for diagnosis and service, see 1989 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 1989 BODY COMPUTER MODULE -- ALLANTE article. 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 lights an "Engine Control System Fault" telltale on the instrument panel to alert the driver that a malfunction has occurred.

Fig 1: Identifying ECM Operating Conditions Sensed & Systems Controlled

Courtesy of GENERAL MOTORS CORP.