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. This will erase any trouble codes stored in ECM.
• DO NOT  cause short circuits when performing electrical tests. This will set additional trouble 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 chassis ground. If coil wire is more than 1/4" from chassis 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 trouble codes, always repair lowest number trouble code first.