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 Engine Control Module (ECM) unless instructed to do so. Doing so will erase any fault codes stored in ECM. Turn ignition off before disconnecting battery or damage to ECM may result.
• DO NOT cause short circuits when performing electrical tests. DO NOT disconnect sensors with ignition on. Either procedure 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, DO NOT hold coil wire more than 1/4" from ground. Damage to vehicle electronics and/or PCM/ECM may result.
• DO NOT prolong testing of fuel injectors. Engine may hydrostatically (liquid) lock.
• The control harness between ECM and Heated Oxygen Sensor (HO2S) has a shield grounded to chassis to prevent electromagnetic interference. If shield is damaged, the control harness must be replaced.