Service Precautions

Before proceeding with diagnosis, following precautions must be observed:

• Ensure vehicle has a fully charged battery and functional charging system. DTCs cannot be retrieved if battery voltage is too low.
• Visually inspect connectors and circuit harness being worked on.
• DO NOT disconnect battery or ECM/PCM. This will erase any DTCs stored in ECM/PCM memory.
• DO NOT cause short circuits when performing electrical tests. This will set additional DTCs, making diagnosis of original problem more difficult.
• DO NOT use a test light in place of a voltmeter. Use voltmeter with 10-megohm impedance.
• 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/PCM may result.
• DO NOT prolong testing of fuel injectors. Engine may hydrostatically (liquid) lock.