1990 Mercury Grand Marquis LSFACTORY OEM SERVICE PROCEDURE

Vehicle Speed Sensor (VSS) Test

Disconnect speed sensor electrical connector. Using DVOM check resistance across sensor terminals. Resistance should be 200-300 ohms. Raise vehicle on hoist. Set DVOM to AC volts and connect across sensor terminals. Operate vehicle on hoist, or road test at approximately 20 MPH and observe DVOM. Voltage should be 1.5-6.5 volts AC.

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:

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

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