Service Precautions

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

• 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.
• When checking for spark, ensure no fuel leaks exist and spark plug cable or coil wire is not more than 1/4" from engine ground. If spark plug or coil wire is more than 1/4" from engine ground, damage to vehicle electronics and/or Powertrain Control Module (PCM) may result.
• DO NOT prolong testing of fuel injectors or engine may hydrostatically lock.
• If replacing PCM, correct vehicle mileage and Vehicle Identification Number (VIN) must be programmed into PCM to prevent DTCs from being set in Anti-Lock Brake System (ABS) module, Air Bag Control Module (ACM) and Sentry Key Immobilizer Module (SKIM), if equipped. See PROGRAMMING  .
• If replacing PCM on models with a Sentry Key Immobilizer Module (Skim), secret key data must be updated to enable engine starting. To update secret key data, see PROGRAMMING  .