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 Powertrain Control Module (PCM) or Engine Control Module (ECM) unless instructed to do so. Doing so will erase any fault codes stored in PCM/ECM. Turn ignition off before disconnecting battery or damage to PCM/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 PCM/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.