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.
• DO NOT use 12-volt test light when checking 5-volt supply circuit, PCI bus circuit, Camshaft Position (CMP) sensor signal circuit, Crankshaft Position (CKP) sensor signal circuit, Oxygen (O2) sensor signal circuit or Vehicle Speed Sensor (VSS) signal circuit. Damage to Powertrain Control Module (PCM) may occur.
• 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, use the terminal side (not the wire end) of the connector. 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 DTC, making diagnosis of original problem more difficult.
• 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 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 Sentry Key Immobilizer Module (SKIM), secret key data must be updated to enable engine starting. To update secret key data, see PROGRAMMING .
• Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal-to-pin connection. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
• The Miller Terminal Removal Pick (3638) must be used to release PCM connector terminals or harness and connector damage will occur.