How To Use Diagnostic Tests
WARNING: This page is about a different car, the 2001 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.
- Do not perform any diagnostic test unless instructed by QUICK TEST or appropriate symptom description under TROUBLE SHOOTING . Follow each test step in order until fault is found. DO NOT replace any part unless directed to do so. When more than one code is retrieved, start with first DTC displayed.
- Diagnostic tests ensure electrical circuits are okay before sensors or other components are replaced. Always test circuits for continuity between sensor and PCM. Test all circuits for short to power, opens or short to ground. Voltage Reference (VREF) and Voltage Power (VPWR) circuits should be tested with ignition switch in ON position or as specified in DIAGNOSTIC TESTS.
- Always backprobe TCM harness connectors. DO NOT connect test light unless specified in testing procedure. All measurements are made by probing rear of connector (wiring harness side). When checking for shorts or continuity, isolate both ends of circuit. Ensure ignition switch is in OFF position (unless instructed otherwise).
- Disconnect solenoids and switches from harness before measuring continuity and resistance or applying voltage. After each repair, check all component connections and repeat RETRIEVING DIAGNOSTIC TROUBLE CODES (QUICK TEST) under SELF-DIAGNOSTIC SYSTEM.
- An open circuit is defined as a resistance reading of greater than 5 ohms. This specification tolerance may be too high for some items in EEC system. If resistance approaches 5 ohms, always clean suspect connector and coat with protective dielectric silicone grease. A short is defined as a resistance reading of less than 10 k/ohms to ground, unless stated otherwise in DIAGNOSTIC TESTS.
- If instructed to replace TCM after performing a diagnostic test, new TCM must be programmed. See PROGRAMMING .