Service Precautions

Before proceeding with diagnosis, following precautions must be observed:

• Ensure vehicle has a fully charged battery and functional charging system.
• Visually inspect connectors and circuit wiring being worked on.
• DO NOT disconnect battery or ECM unless instructed to do so. Doing so will erase any fault codes stored in ECM.
• DO NOT cause short circuits when performing electrical tests. This will set additional fault codes, making diagnosis of original problem more difficult.
• DO NOT use a test light in place of a voltmeter.
• When checking for spark, ensure coil wire is NOT more than 1/4" from ground. If coil wire is more than 1/4" from ground, damage to vehicle electronics and/or ECM may result.
• DO NOT prolong testing of fuel injectors. Engine may hydrostatically (liquid) lock.
• When a vehicle has multiple fault codes, always repair lowest number fault code first, then repair codes in ascending numerical order.