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How To Use Circuit Tests

  1. DO NOT perform any CIRCUIT TEST unless told to do so by QUICK TEST  . Make sure all non-EEC related faults are corrected. Do not replace any part unless directed to do so. When more than one service code is received, start with the first code displayed.
    NOTE: Procedures in the TESTING section of this article are not in absolute numerical order. Procedures not related to this engine have been removed to eliminate confusion.
  2. Do not measure voltage or resistance at ECA or connect any test lamps to it, unless specified. All measurements are made by probing REAR of connector. Isolate both ends of a circuit and turn key off whenever checking for shorts or continuity, unless specified.
  3. Disconnect solenoids and switches from harness before measuring continuity, resistance, or applying 12 volts. Follow each test step in order until fault is found. After each repair, check all component connections and repeat CIRCUIT TEST(S).
  4. An "open" is defined as any resistance reading higher than 5 ohms, unless specified in CIRCUIT TEST. A "short" is defined as any resistance reading less than 10,000 ohms to ground, unless specified in CIRCUIT TEST.
  5. On TEST W  , to prevent replacement of good components, be aware that the following non-EEC related areas may also be at fault. These areas include ignition coil, distributor cap and rotor, spark plug wires, fouled spark plugs, CNAP problems, EGR valve and gasket, air filter, poor power and ground circuits, fuel pressure, intake and exhaust manifold leaks, engine not at normal operating temperature, and problems with PCV valves or fuel contaminated engine oil.
    NOTE: Fuel contaminated engine oil may affect some service codes. If this is suspected, remove PCV valve from valve cover and repeat QUICK TEST  . If problem is corrected, change engine oil and filter.
  6. On TEST W  , vacuum leaks in non-EEC related areas may also cause code 41 or 91 to be displayed. Check for unmetered air between airflow meter and throttle body, leaking vacuum motors, engine seals, EGR system, PCV system, canister purge (CANP) problems, or contaminated HEGO sensor. Code 42 or 92 may be caused by fuel contaminated engine oil, ignition misfire, EGR system, or CANP problems.
NOTE: In the following diagnostic charts, circuits and illustrations are supplied courtesy of Ford Motor Co.
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