Diagnostic Aids

This system test is only intended to diagnose the following components and circuits.

Vehicle Wiring Harness Circuits: Vehicle Power (VPWR), IGN START/RUN, Battery Positive Voltage (B+) & Power Relay Ground
Power Relay

1) Check VPWR Circuit Resistance

Turn ignition switch to OFF position. Disconnect Idle Air Control (IAC) solenoid. Disconnect scan tool. Disconnect power relay. Measure resistance of VPWR circuit between IAC valve harness connector and power relay. See Fig 1-Fig 4 . If resistance is less than 5 ohms, reconnect IAC valve and go to next step. If resistance is 5 ohms more, repair open in VPWR circuit between power relay and IAC valve.

Fig 1: Identifying Power Relay Circuits (Contour, Cougar, Focus & Mystique)
Courtesy of FORD MOTOR CO.

Fig 2: Identifying Power Relay Circuits (LS)
Courtesy of FORD MOTOR CO.

Fig 3: Identifying Power Relay Circuits (Sable & Taurus)
Courtesy of FORD MOTOR CO.

Fig 4: Identifying Power Relay Circuits (All Other Models)
Courtesy of FORD MOTOR CO.

2) Check Voltage To Power Relay

Ensure ignition switch is in OFF position and power relay is disconnected. Measure voltage between ground and B+ terminal at power relay harness connector. Note voltage reading. Turn ignition switch to ON position. Measure voltage between ground and IGN START/RUN terminal at power relay harness connector. If any voltage is 10.5 volts or less, repair open circuit. If both voltage measurements are more than 10.5 volts, go to next step.

3) Check Ground Circuit To Power Relay

Measure voltage between ground terminal and B+ terminal at power relay harness connector. If voltage is more than 10.5 volts, replace power relay. If voltage is 10.5 volts or less, repair open in ground circuit.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 5). No test procedures have been omitted.

NOTE: VPWR fuse No. 111 (15-amp), feeds HO2S heater, SSR (air pump relay) and WOT A/C cutoff relay circuits. VPWR fuse No. 112 (10-amp), feeds Coil-On-Plug (COP) and ignition transformer capacitor circuits. For fuse locations, see WIRING DIAGRAMS article.

5) Open VPWR Circuit (LS): Check Fuse
Remove and inspect suspect VPWR fuse No. 111 (15-amp) or No. 112 (10-amp) to component where VPWR check failed. If suspect fuse is okay, go to next step. If suspect fuse is blown, check VPWR circuit for short to ground between blown fuse and appropriate component. See WIRING DIAGRAMS article. Repair as necessary. Replace VPWR fuse.

6) Check Power To Other VPWR Circuit Fuse

Remove and inspect other VPWR circuit fuse that goes to components supplied by power relay No. 2. Replace fuse as necessary. Turn ignition switch to ON position. Measure voltage between negative battery terminal and both VPWR circuit fuse harness connectors from power relay No. 2. If both voltage measurements are more than 10.5 volts, repair open between fuse and component. If both voltages are 10.5 volts or less, go to next step. If only one measurement is 10.5 volts or less, repair open in VPWR circuit between fuse and splice.

7) Check VPWR Circuit Continuity Between Fuse & Power Relay No. 2

Turn ignition switch to OFF position. Disconnect power relay No. 2. Measure resistance of VPWR circuit between power relay No. 2 and either fuse. If resistance is less than 5 ohms, return to step 2). If resistance is 5 ohms more, repair open in VPWR circuit between power relay No. 2 and splice.