If equipped with electric lead to ported vacuum switch, disconnect lead from PVS and ground to chassis. Verify that harness connector at speed sensor is firmly attached.
Check for proper operation by slowly accelerating engine to above 1950 RPM. Throttle modulator should activate at about 1850 RPM (increasing engine speed) and deactivate at about 1600 RPM (decreasing engine speed). If not, proceed to next step.
Disconnect harness at speed sensor. Turn ignition switch on. Connect one lead of a voltmeter to terminal No. 1 and other lead to ground. Battery voltage should be indicated. If not, repair or replace wiring as necessary. Repeat voltage test on terminal No. 4.
NOTE: Terminals are numbered 1 through 6, starting at key side. Terminal No. 2 is blank.
Connect one voltmeter lead to terminal No. 6, and other lead to ground. Voltmeter should indicate a minimum of 12 volts. If not, repair or replace wiring as necessary.
Turn ignition off. Connect one ohmmeter lead to terminal No. 3 of connector, and other lead to terminal No. 1. Ohmmeter should read continuity. If not, repair or replace wiring. Repeat test on terminals No. 5 and 1.
If throttle modulator does not actuate, or readings are not as indicated, speed sensor is faulty and must be replaced. Reconnect all wiring to original positions.

Fig 1: Schematic of Decel Throttle Modulator System

Courtesy of FORD MOTOR CO.

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.

Safety Warning

Electronic Speed Sensor Test