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.
1998 Mercury Villager GS, Van CargoFACTORY OEM SERVICE PROCEDURE
How To Use Circuit Tests
- Ensure all non-engine control related faults found while performing BASIC DIAGNOSTIC PROCEDURES in BASIC TESTING article have been corrected. DO NOT perform any circuit test unless instructed by QUICK TEST or another circuit test step. Follow each test step in order until fault is found. DO NOT replace any part unless directed to do so. When more than one code is retrieved, start with first code displayed.
- Circuit tests ensure electrical circuits are okay before sensors or other components are replaced. Always test circuits for continuity between sensor and PCM. Test all circuits for short to power, opens or short to ground. Voltage Reference (VREF) and Voltage Power (VPWR) circuits should be tested with ignition on or as specified in circuit tests.
- DO NOT make voltage or resistance measurement by probing PCM connector, as harness and connector are easily damaged. DO NOT connect any test light unless specified in testing procedure. All measurements are made by probing rear of connector (wiring harness side) unless instructed otherwise. Isolate both ends of a circuit and turn ignition off when checking for shorts or continuity, unless instructed otherwise.
- Disconnect solenoids and switches from harness before measuring continuity and resistance or applying voltage. After each repair, check all component connections and repeat QUICK TEST .
- An open circuit is defined as a resistance reading of greater than 5 ohms, however; this specification may be too high for some items. If resistance approaches 5 ohms, always clean suspect connector and coat it with protective dielectric silicone grease. A short is defined as a resistance reading of less than 10,000 ohms to ground, unless stated otherwise in circuit test.
NOTE:
In following tests, circuit diagrams and illustrations are courtesy of Ford Motor Co.
Factory Service Tools
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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.
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