Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 26 other vehicles, including the 1999 Mercury Tracer, 1999 Mercury Sable, 1999 Mercury Mystique, 1999 Mercury Mountaineer, and 1999 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when directed by QUICK TEST. This test is intended to diagnose the following:

Generator/regulator.
Wiring harness circuits (GEN-MON, GEN-COM and BATT-SENSE).
Powertrain Control Module (PCM).

1) DTC P1246: Verify Generator Drive Function

Check generator drive belt condition and tension. Start engine and verify generator is turning. Repair as necessary. If no faults are found, go to next step.

2) Verify Generator Is EEC Controlled

Turn igniton off. Disconnect negative then positive battery cable. Disconnect generator connector. Measure resistance between BATT-SENSE terminal and GEN-COM terminal at generator wiring harness connector. See Fig 1. If resistance is not 950-1050 ohms, replace generator. If resistance is 950-1050 ohms, go to next step.

Fig 1: Identifying Generator Wiring Harness Connector Terminals (Windstar)
Courtesy of FORD MOTOR CO.

3) Check Battery Sensor Voltage

Reconnect generator connector. Reconnect battery terminals. Measure voltage across battery terminals. Note voltage reading. Measure voltage between ground and BATT-SENSE terminal at generator wiring harness connector. If voltage is within .5 volt (plus or minus) of battery voltage reading, go to next step. If voltage is not within .5 volt of battery voltage reading, repair BATT-SENSE circuit as necessary.

4) Check Generator Failure Mode

Ensure all accessories are off. Using scan tool, select AFS PID from PID/DATA monitor menu. Start engine. Increase engine speed to 2000 RPM. Note PID reading. Wiggle and bend wiring harness between generator and PCM. Fault is indicated by a change in PID value. If a fault is indicated, go to next step. If no fault is indicated, check charging system and repair as necessary.

5) Check For Short To Power

Turn ignition off. Disconnect PCM 104-pin connector. Disconnect generator connector. Turn ignition on. Measure voltage between PCM connector pin No. 20 and chassis ground. If voltage is .5 volt or less, go to next step. If voltage is .5 volt or more, repair short to power in GEN-MON circuit.

6) Check For Short To Ground

Turn ignition off. Measure resistance between PCM connector pin No. 20 and chassis ground. If resistance is more than 10,000 ohms, go to next step. If any resistance is 10,000 ohms or less, repair short to ground in GEN-MON circuit.

7) Check For Open Circuit

Measure resistance between PCM connector pin No. 20 and GEN-MON terminal at generator wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in GEN-MON circuit.

8) Check Generator Monitor Signal

Reconnect all connectors. Start engine and allow to idle. Using scan tool, select AFS PID from PID/DATA monitor menu. If PID frequency is 100-175 Hz and duty cycle is 6-98 percent, go to next step. If PID frequency and duty cycle are not as specified, replace generator.

9) Check Generator Communicator Signal

While observing PID value as in step 8) , turn headlights on and off. If PID value switched from zero to 100-175 Hz and duty cycle switched from one to 99 percent, no problem is indicated at this time. Test is complete. If PID value and duty cycle did not switch as specified, replace PCM.