Engine Controls - Basic Diagnostic Procedures: Introduction
CAUTION:
When battery or ECM is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until adaptation systems have completed a relearn cycle. See 2002 COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.
NOTE:
Before disconnecting battery, obtain anti-theft code for radio. After reconnecting battery, re-code and check operation of anti-theft radio. Also check operation of clock and power windows. On vehicles equipped with Audi Telematics by OnStar(R), switch-off the emergency (back-up) battery for the Telematic/Telephone Control Module prior to disconnecting vehicle battery. Emergency battery is turned on and off using VAG 1551/VAG 1552 or VAS 5051/VAS 5052 scan tool in address word 75 - TELEMATICS set to function 10 - ADAPTATION CHANNEL 08.
NOTE:
To properly diagnose vehicle, vehicle manufacturer recommends use of Scan Tool (VAG 1551/VAG 1552, VAS 5051/VAS 5052) and Test Box (VAG 1598). Generic scan tools may not be capable of performing all diagnostic functions e.g. Readiness Code, Idle Check and Automatic Test Sequence etc. Ensure ignition switch is in OFF position when performing resistance tests. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.
NOTE:
During some of the tests the ECM may identify and record malfunctions. DTC memory should therefore be checked and (if necessary) erased after completing testing and any repair work that may be required.
Before proceeding with basic diagnostic procedures, ensure testing procedure is followed, as some systems which may result in a no-start condition may cause a Diagnostic Trouble Codes (DTC) to be stored in the Engine Control Module (ECM). See SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
If no-start condition still exists after checking and repairing all DTCs, perform a careful and complete visual inspection. Many problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. See VISUAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS. Before condemning the computerized system, perform each test listed in this article.