How To Use Circuit Tests

DO NOT perform any CIRCUIT TEST unless directed to do so by a QUICK TEST procedure. Ensure all non-EEC related faults are 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 service code is received, start with the first code displayed.
CIRCUIT TESTS require that you prove the electrical circuits are okay before you replace sensors or any other components. Always test circuits for continuity between the sensor and the ECA. Test all circuits for shorts to power, opens, or shorts to ground. Voltage Reference (VREF) and Voltage Power (VPWR) circuits should be tested with KOEO or as specified in CIRCUIT TESTS.
DO NOT measure voltage or resistance at ECA or connect any test light, unless specified in testing procedure. 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.
NOTE: When directed in testing procedure to service or repair TFI ignition system, see IGNITION SYSTEM - TFI-IV article in ENGINE section.
Disconnect solenoids and switches from harness before measuring continuity, resistance, or applying voltage. After each repair, check all component connections and repeat CIRCUIT TEST.
An "open" is defined as any resistance reading greater than 5 ohms. This specification tolerance may be too high for some items in the EEC-IV system. If resistance approaches 5 ohms, always clean the suspected connector and coat with protective dielectric silicone grease. A "short" is defined as any resistance reading less than 10K ohms to ground, unless otherwise specified in CIRCUIT TEST.
On FUEL CONTROL CIRCUIT TESTS C1, and C2, 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, canister purge 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.
On FUEL CONTROL CIRCUIT TESTS C1, and C2, vacuum leaks in non-EEC related areas may also cause code 41 or 91 to be displayed. Check for unmetered air leaks 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 tests, circuits and illustrations are supplied courtesy of Ford Motor Co.

NOTE: CIRCUIT TESTS are grouped in the following categories.
- A1-A3 Preliminary Tests
- B1-B15 Input Sensor Tests
- C1-C2 Fuel Control Systems
- D1-D24 ECA Output Tests