Engine Controls - System & Component Testing: Introduction
WARNING:
DO NOT touch or disconnect ignition system wires when the engine is running or being cranked at starting RPM. DO NOT operate the starter if the fuel injectors have been removed. Be sure the ignition is switched OFF, when disconnecting ignition wires, disconnecting fuel injection system wiring, connecting or disconnecting test equipment leads disconnecting the battery or washing the engine compartment.
WARNING:
Before cranking the engine at starting RPM (such as for compression testing) disable the ignition and fuel injection systems: Disconnect the ignition coil power output stage. Disconnect harness connectors from all fuel injectors. After the work is completed, erase Diagnostic Trouble Code (DTC) memory.
CAUTION:
Before disconnecting the battery. Stop the engine. Be sure the ignition is switched off (also applies when connecting the battery). Failure to do so may damage the Engine Control Module (ECM). Be sure the battery negative (-) cable is disconnected, when: Working on the electrical system. Resistance (spot) welding or electric arc welding anywhere on the vehicle. When connecting and disconnecting electrical test equipment (LED voltage tester, multimeter, etc.): Ensure the ignition is switched off. Use correct adapters from the (VW 1594) connector test kit, for any work affecting the Engine Control Module (ECM). BEFORE disconnecting the ECM harness connector, switch the ignition off and wait at least 20 seconds. Failure to do so may damage the ECM. DO NOT connect any outside voltage source to stimulate an output signal at the ECM.
CAUTION:
When battery is disconnected, vehicle computer may lose memory data and Diagnostic Trouble Codes (DTCs) will be erased. Driveability problems may exist until vehicle is driven for 5-10 minutes. See TEST DRIVE .
CAUTION:
Some vehicles may be equipped with anti-theft radio, when battery is disconnected, radio will go into anti-theft protection mode. Obtain radio anti-theft protection code from owner prior to servicing vehicle.
Before testing separate components or systems, perform a visual inspection. See VISUAL INSPECTION . Since many computer-controlled and monitored components set a trouble code if they malfunction, see SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article. If no Diagnostic Trouble Codes (DTCs) are present and a no start condition exists, proceed to BASIC DIAGNOSTIC PROCEDURES article. 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.).
After any repairs are made, test drive vehicle. See TEST DRIVE .
NOTE:
Testing individual components does not isolate shorts or opens. Perform all voltage and continuity tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens. Manufacturer recommends using Scan Tool (VAG 1551), Test Box (VAG 1598) and Connector Test Kit (VW 1594).