How To Use System Tests
- Ensure all non-EEC related faults found while performing basic diagnostic procedures in BASIC DIAGNOSTIC PROCEDURES article have been corrected. 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 code displayed.
- System 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 SYSTEM TESTS.
- If measuring voltage or resistance at PCM and a breakout box is not available, always backprobe PCM harness connector. See Fig 1. DO NOT connect any test light unless specified in testing procedure. All measurements are made by probing rear of connector (wiring harness side). Isolate both ends of a circuit and turn ignition switch to OFF position when checking for shorts or continuity, 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 QUICK TEST .
- An open circuit is defined as a resistance measurement of 5 ohms or more. This specification tolerance may be too high for some items in EEC-V system. If resistance approaches 5 ohms, always clean suspect connector and coat it with protective dielectric silicone grease. A short is defined as a resistance measurement of 10 k/ohms or less to ground, unless stated otherwise in system test.
- If instructed to replace Powertrain Control Module (PCM) after performing a system test, new PCM must be programmed. See PROGRAMMING PCM .
Courtesy of FORD MOTOR CO.