Diagnostic Aids

Fuel-contaminated engine oil may affect some codes. If oil is suspect, remove PCV valve from valve cover and repeat QUICK TEST . If problem is corrected, change engine oil.

On CIRCUIT TEST H and CIRCUIT TEST J, vacuum leaks in non-EEC related areas may cause Code 41 or 91 to be displayed. Check vacuum motors, engine seals, EGR system, PCV system, Canister Purge (CANP), HEGO sensor and between airflow meter and throttle body for unmetered air leaks. Code 42 or 92 may be caused by fuel-contaminated engine oil, ignition misfire, or EGR system or CANP problems.

NOTE: In following tests, circuit diagrams and illustrations are courtesy of Ford Motor Co.

CIRCUIT TESTS are grouped as follows:

A-C - No Start & Voltage Tests.
DA-DS - Input Sensor Tests.
FD-FF - Additional Input Component Tests.
G-J - Fuel Control Systems.
KC-X - ECA (Processor) Output Tests.