Diagnostic Aids

Perform this test when directed by QUICK TEST. This test is intended to diagnose a faulty BPP switch, circuit or PCM. Brake Pedal Position (BPP) switch is also referred to as a Brake On/Off (BOO) switch. To prevent replacement of good components, be aware following non-EEC related areas may be at fault:

• Brakelight bulb.
• Brakelight switch or brakelight fuse.

1. 1) KOER DTC P0703 Or P1703: Verify Brake Pedal Was Depressed
   
   These DTCs indicate that when brake pedal was applied during KOER ON-DEMAND SELF-TEST, BPP signal did not cycle high and low. Possible causes for this fault are:
   • Brake pedal not applied during self-test.
   • Brake pedal applied during entire self-test.
   • Open or short brakelight circuit.
   • Open or short BPP circuit.
   • Faulty BPP switch.
   • Faulty Lighting Control Module (Continental and Town Car).
   • Faulty Rear Electronic Module (Windstar).
   • Faulty Powertrain Control Module (PCM).

   If brake was not applied and released during KOER ON-DEMAND SELF-TEST , repeat test. Depress and release brake pedal only once during test. If pedal was applied and released, proceed as follows:

   • On Continental and Town Car, diagnose Lighting Control Module (LCM) and/or related system. See appropriate MODULE COMMUNICATIONS article in ACCESSORIES & EQUIPMENT in appropriate lemon-25® manual.
   • On Windstar, diagnose Rear Electronic Module (REM) and/or related system. See MODULE COMMUNICATIONS - WINDSTAR article in ACCESSORIES & EQUIPMENT in appropriate lemon-25® manual.
   • On all other models, go to step  3).

2. 2) KOEO DTC P0703 Or P1703
   
   These DTCs indicate that BPP signal voltage was high during KOEO ON-DEMAND SELF-TEST. Possible causes for these faults are:
   • Brake pedal applied during self-test.
   • Open or short BPP circuit.
   • All brakelights open.
   • Faulty brakelight ground.
   • Faulty BPP switch.

   If brake was applied during KOEO ON-DEMAND SELF-TEST, repeat test. DO NOT apply brake during self-test. If pedal was not applied, proceed as follows:

   • On Continental and Town Car, diagnose Lighting Control Module (LCM) and/or related system. See appropriate MODULE COMMUNICATIONS article in ACCESSORIES & EQUIPMENT.
   • On Windstar, diagnose Rear Electronic Module (REM) and/or related system. See appropriate MODULE COMMUNICATIONS - WINDSTAR article in ACCESSORIES & EQUIPMENT.
   • On all other models, go to next step.

3. 3) Continuous Memory DTCs P0703 Or P1703: Check Operation Of Brakelights
   
   This DTC indicates a BPP switch input fault. Possible causes for this fault are:
   • Open or short BPP circuit.
   • Faulty BPP switch.
   • Faulty Powertrain Control Module (PCM).

   Check operation of brakelights. If brakelights operate normally, go to next step. If brakelights do not operate properly, go to step  5) (brakelights never on) or step  7) (brakelights always on).

4. 4) Check For BPP PID Cycling
   
   Turn ignition on. Using scan tool, select BPP PID from PID/DATA monitor menu. While observing PID, apply and release brake several times.
   NOTE: If BPP PID is not available, go to step  10).

   If PID does not cycle ON and OFF, go to step  10). If PID cycles ON and OFF, go to TEST Z .

5. 5) Check For Power To BBP Switch
   
   Ensure brakelight bulbs are good. Disconnect BPP switch (located on brake pedal). Measure B+ input voltage between BPP switch wiring harness connector and chassis ground. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open in B+ circuit to BPP switch.
6. 6) Check BPP Switch
   
   Depress brake pedal. Measure resistance between BPP switch terminals. If resistance is 5 ohms or more, replace BPP switch. If resistance is less than 5 ohms, repair open circuit between BPP switch and brakelight ground.
7. 7) Verify BPP Switch Is Not Always Closed
   
   Ensure ignition is off. Disconnect BPP switch (located on brake pedal). Turn ignition on. If brakelights are still on, go to next step. If brakelights are off, verify correct installation of BPP switch. If installation is okay, replace BPP switch.
8. 8) Check For Short To Power In PCM
   
   Turn ignition off. Disconnect PCM 104-pin connector. Turn ignition on. Check brakelights. If brakelights are still on, go to next step. If brakelights are off, replace PCM.
9. 9) Check For Short To Power
   
   Turn ignition off. Ensure PCM and BPP switch are disconnected. One at a time, disconnect all modules associated with brakelight circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. After disconnecting each module, turn ignition on and check brakelights. Turn ignition off. Repeat until each associated module has been disconnected or brakelights turn off. If brakelights are still on after disconnecting all associated modules, repair short to power in BPP circuit. If brakelights are off with associated module(s) disconnected, diagnose appropriate module and/or related system. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT in appropriate lemon-25® manual to determine articles that are associated with module that was disconnected to eliminate short to power. Repair system or replace module as necessary.
10. 10) Check For BPP Circuit Cycling
    
    Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure voltage between PCM connector pin No. 92 and chassis ground while applying and releasing brake. If voltage cycles on and off, replace PCM. If voltage does not cycle, repair open in BPP circuit between PCM and BPP circuit connection to brakelight B+ circuit.