Service Precautions

Before proceeding with system diagnosis, following precautions must be followed:

• Engines produce carbon monoxide that is odorless, causes slower reaction time, and can lead to serious injury. When the engine is operating, keep service areas well ventilated or attach the vehicle exhaust system to the shop exhaust removal system.
• Set the parking brake and block the wheels before testing or repairing the vehicle. It is especially important to block the wheels on front-wheel drive vehicles; the parking brake does not hold the drive wheels.
• When servicing a vehicle, always wear eye protection, and remove any metal jewelry such as watchbands or bracelets that might make an inadvertent electrical contact.
• Ensure fuel pressure is released before disconnecting any fuel line or fuel fitting, as fuel system is under pressure and may cause personal injury. See FUEL SYSTEM PRESSURE RELEASE .
• When using diagnostic tests for diagnosis, DO NOT skip any steps or incorrect diagnosis may result. When instructed to disconnect any connector, check that the connector is clean and in good condition after disconnecting the connector. Repair or clean connector as necessary. Always perform indicated verification procedure after repairs are made. Verification tests are listed at the end of the diagnostic tests.
• When using a jumper wire, ensure either jumper wire or circuit is fuse-protected.
• Ensure ignition is off before disconnecting connector from any control module.
• When checking voltage or continuity at any control module, probe connector for control module from pin side. DO NOT probe wire through insulation or backprobe connector (unless instructed to do otherwise in test procedure).
• DO NOT cause short circuits when performing electrical tests. This will set additional Diagnostic Trouble Codes (DTC), making diagnosis of original problem more difficult.
• DO NOT prolong testing of fuel injectors or engine may hydrostatically lock.
• If replacing Powertrain Control Module (PCM), correct vehicle mileage and Vehicle Identification Number (VIN) must be programmed into PCM to prevent DTCs from being set in Controller Anti-Lock Brake (CAB) module, Air Bag Control Module (ACM) and Sentry Key Immobilizer Module (SKIM), if equipped. See PROGRAMMING .
• If replacing PCM on models with a SKIM, secret key data must be updated to enable engine starting. To update secret key data, see PROGRAMMING .