Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMERCURY1991TRACER BASE, 4D SEDAN, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 94 (ENGINE CONTROLS - TESTS W/CODES - EEC-IV)CIRCUIT TESTSCIRCUIT TEST QC - OUTPUT STATE CHECK NOT FUNCTIONINGDIAGNOSTIC AIDS
1991 Mercury Tracer Base, 4D Sedan, Automatic
Diagnostic Aids
1991 Mercury Tracer Base, 4D Sedan, AutomaticSECTION Diagnostic Aids
WARNING: This page is about a different car, the 1995 Lincoln Mark VIII. However, it is still accessible from the selected car via links, so may be relevant.
Perform this circuit test when directed by other CIRCUIT TESTS. This test is only intended to diagnose:
- Throttle plate linkage.
- Test conditions.
- Check For Codes 121, 122 & 123
Disconnect cruise control servo wiring harness connector (if equipped). Perform KOEO SELF-TEST . If Code 121, 122 or 123 is present, go to appropriate CIRCUIT TEST. See DIAGNOSTIC TROUBLE CODE REFERENCE CHARTS , and service codes as necessary. If Code 111 (pass code) is displayed, go to next step. If no code is displayed, go to CIRCUIT TEST QA . - Check Throttle Linkage
Check throttle and linkage for sticking and binding. If throttle and linkage are okay, replace Throttle Position (TP) sensor and repeat QUICK TEST . If throttle or linkage is binding, repair as necessary and repeat QUICK 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.