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 TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

The Port Fuel Injection (PFI) system combines engine control, fuel metering and emission monitoring into a computer controlled system. The Electronic Control Module (ECM) is the "brain" of the PFI system. The ECM is a digital electronic computer which receives and processes engine sensor data, computes and interprets engine information, and sends instructions to various components. See Fig 1 . It provides fuel efficient operation with reduced exhaust emissions.

Vehicle is also equipped with a Body Control Module (BCM) that is used to control various vehicle body functions based upon data sensor and switch inputs. The ECM and BCM exchange information to maintain efficient operation of all vehicle functions. This transfer of information gives the BCM control over the ECM's self-diagnostic capabilities as well as its own.

Fig 1: Identifying PFI Component Locations

Courtesy of GENERAL MOTORS CORP.

The PFI system consists of the following sub-systems: fuel delivery and control, air induction, data sensors, Electronic Control Module (ECM), Body Control Module (BCM), Electronic Spark Timing (EST), Idle Speed Control (ISC), emission controls, closed loop fuel control, cruise control, diagnostic system, and Viscous Converter Clutch (VCC). See Fig 2 .

Fig 2: Identifying PFI Systems Sensed & Controlled

Courtesy of GENERAL MOTORS CORP.