Service Precautions

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

• Ensure fuel pressure is released before removing fuel line or fittings, as fuel system is under pressure and may cause personal injury.
• 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 if 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 or 8-volt supply circuit, CCD bus circuit, camshaft position sensor signal circuit, crankshaft position sensor signal circuit, oxygen sensor signal circuit or vehicle speed sensor signal circuit or Powertrain Control Module (PCM) may be damaged.
• When using a jumper wire, ensure either jumper wire or circuit is fuse-protected.
• Before disconnecting any control module connector, ensure ignition is off before removing connector.
• When checking voltage or continuity at any control module, probe control module connector from pin side. DO NOT backprobe connector unless instructed to in test procedure. DO NOT probe wires through the insulation.
• DO NOT cause short circuits when performing electrical tests. This may cause additional Diagnostic Trouble Codes (DTC) to be set, making diagnosis of original problem more difficult.
• Use specified test equipment when performing electrical tests.
• DO NOT prolong testing of fuel injectors or engine may hydrostatically lock.
• If replacing PCM, the correct vehicle mileage and Vehicle Identification Number (VIN) must be programmed into the PCM to prevent DTC from being set in Anti-Lock Brake System (ABS) module and Supplemental Restraint System (SRS) module. See POWERTRAIN CONTROL MODULE PROGRAMMING  under PROGRAMMING.
• On 4.7L, if Transmission Control Module (TCM) is replaced, perform shift quality quick learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION.
  CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.