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HOMESERVICE MANUALSMERCURY1991TRACER BASE, 4D SEDAN, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 41 (ENGINE CONTROLS - TESTS W/CODES - EEC-IV (5.0L))QUICK TESTKOEO SELF-TEST
1991 Mercury Tracer Base, 4D Sedan, Automatic

KOEO Self-Test

1991 Mercury Tracer Base, 4D Sedan, AutomaticSECTION KOEO Self-Test
WARNING: This page is about a different car, the 1994 Ford Mustang. However, it is still accessible from the selected car via links, so may be relevant.

Ensure engine is warmed to normal operating temperature. If engine does not start (or stalls after starting), continue KOEO SELF-TEST. DO NOT depress throttle. Turn ignition off. Ensure test equipment is properly attached. Turn ignition on (engine off). Record all KOEO and Continuous Memory Codes.

If a Code 111 (pass code) is not retrieved, service KOEO codes. See DIAGNOSTIC TROUBLE CODE REFERENCE CHARTS. If PCM will not output codes, go to CIRCUIT TEST QA. If diagnostic trouble codes are retrieved:

  • If MIL/CHECK ENGINE light is on, service diagnostic trouble codes in order retrieved. See DIAGNOSTIC TROUBLE CODE REFERENCE CHARTS.
  • On distributorless ignition models, see IGNITION SYSTEM in SYSTEM/COMPONENT TESTS - EEC-IV (5.0L) article in the ENGINE PERFORMANCE section if Continuous Memory Code 215, 216, 217, 218, 222, 223, 224, 232 or 238 is retrieved during KOEO SELF-TEST.
  • If vehicle has a no-start condition, go to CIRCUIT TEST AA (DI), CIRCUIT TEST AB (EI - low data rate) or CIRCUIT TEST AC (EI -high data rate).
  • If vehicle displays a Code 111 (pass code) and does not have any symptoms described in previous steps, go to KOER SELF-TEST.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.