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Test FD: Brake Pedal Position Switch: Testing

    NOTE: For additional testing information, see DIAGNOSTIC AIDS .

  1. 1) For KOER Only DTCs P0703 & 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:
    • Open Or Short In BPP Circuit
    • Open Or Short In Brakelight Circuit
    • Faulty Powertrain Control Module (PCM)
    • Faulty Rear Electronic Module (LS, Thunderbird & Windstar)
    • Faulty Lighting Control Module (Town Car)
    • Faulty BPP Switch
    • Misadjusted Brake Switch
    • Brake Pedal Not Applied During KOER On-Demand Self-Test

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

    • On Town Car, diagnose Lighting Control Module (LCM) and/or related system. See SYSTEM TESTS in appropriate AUTOLAMP SYSTEMS article in ACCESSORIES & EQUIPMENT.
    • On Windstar, diagnose Rear Electronic Module (REM) and/or related system. See SYSTEM TESTS in appropriate AUTOLAMP SYSTEMS article in ACCESSORIES & EQUIPMENT.
    • On Expedition and Navigator, diagnose anti-lock brake system. See appropriate ANTI-LOCK article in BRAKES.
    • On all others, go to step  3).

    2. NOTE: For additional testing information, see DIAGNOSTIC AIDS .

  2. 2) For KOEO Only DTCs P0703 & P1703: Verify Brake Pedal Was Not Applied
    These DTCs indicate that BPP signal voltage was high during KOEO on-demand self-test. Possible causes for these faults are:
    • Open Or Short In BPP Circuit
    • Open Or Short In Brakelight Circuit
    • Faulty Powertrain Control Module (PCM)
    • Faulty Rear Electronic Module (LS & Windstar)
    • Faulty Lighting Control Module (Town Car)
    • Faulty BPP Switch
    • Misadjusted Brake Switch
    • Brake Pedal Applied During Entire KOEO On-Demand Self-Test

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

    • On Town Car, diagnose Lighting Control Module (LCM) and/or related system. See SYSTEM TESTS in appropriate AUTOLAMP SYSTEMS article in ACCESSORIES & EQUIPMENT.
    • On Windstar, diagnose Rear Electronic Module (REM) and/or related system. See SYSTEM TESTS in appropriate AUTOLAMP SYSTEMS article in ACCESSORIES & EQUIPMENT.
    • On Expedition and Navigator, diagnose anti-lock brake system. See appropriate ANTI-LOCK article in BRAKES.
    • On all others, turn ignition switch to ON position and go to next step.

    3. NOTE: For additional testing information, see DIAGNOSTIC AIDS .

  3. 3) For Continuous Memory Only DTCs P0703, & For KOER & Continuous Memory Only DTC P1572: Check Operation Of Brakelights
    These DTCs indicate brake input rationality tests (one or both BPA or BPP switch inputs to PCM) failed to change when expected. Possible causes are:
    • Misadjusted Brake Switch
    • Blown Fuse
    • Faulty BPP Switch
    • Faulty BPA Switch
    • Open Or Short In BPP Circuit
    • Open Or Short In BPA Circuit
    • Faulty Powertrain Control Module (PCM)

    Check operation of brakelights. If brakelights operate normally, go to next step. If brakelights do not operate properly, on LS and Thunderbird, diagnose Rear Electronic Module (REM) and/or related system. See SYSTEM TESTS in appropriate AUTOLAMP SYSTEMS article in ACCESSORIES & EQUIPMENT. On all others, go to step  5) (brakelights inoperative), or step  7) (brakelights always on).

  4. 4) Check For PCM BPP PID Cycling

    Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to ON position. Using scan tool, access BPP PID from PID/DATA MONITOR & RECORD menu.
    NOTE: If BPP PID is not accessible, go to step  10).

    While observing BPP PID, apply and release brake pedal several times. If BPP PID does not cycle ON and OFF, go to step  10). If BPP PID cycles ON and OFF, go to step  14) (for DTC P1572), or go to TEST Z, step 1) (for all others).

  5. 5) Check B+ Voltage To BPP Switch

    Ensure brakelight bulbs are okay. Disconnect BPP switch (located on brake pedal). Using a DVOM, measure voltage between B+ circuit at BPP switch harness connector and chassis ground. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, check fuse for B+ circuit to BPP switch. If fuse is okay, repair open in B+ circuit to BPP switch. If fuse is blown, repair short to ground in B+ circuit, BPP or brakelight PWR circuit. See EXTERIOR LIGHTS in SYSTEM WIRING DIAGRAMS in ELECTRICAL.

  6. 6) Verify Integrity Of BPP Switch

    Using a DVOM, measure resistance between appropriate BPP switch terminals. See Figure-Figure . Observe resistance measurement while applying brake pedal. If resistance is 5 ohms or more with brake pedal applied, replace BPP switch. If resistance is less than 5 ohms with brake pedal applied, repair open circuit between BPP switch and brakelight ground.

  7. 7) Verify BPP Switch Is Not Always Closed

    Disconnect BPP switch (located on brake pedal). Turn ignition switch to ON position. If brakelights are still illuminated, go to next step. If brakelights are now 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 switch to OFF position. Disconnect PCM connector(s). Turn ignition switch to ON position. If brakelights are still illuminated, go to next step. If brakelights are now off, replace PCM.

  9. 9) Check Brakelight Circuit For Short To Power In Harness

    Turn ignition switch to OFF position. Ensure PCM and BPP switch are disconnected. One at a time, disconnect modules associated with brakelight circuit. See WIRING DIAGRAMS . After disconnecting an associated module, turn ignition switch to ON position and check brakelights. Turn ignition switch to OFF position. 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 brakelight circuit. See EXTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT. If brakelights are off with associated module(s) disconnected, diagnose appropriate module and/or related system. Repair system or replace module as necessary.

  10. 10) Check For BPP Circuit Cycling

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. For Aviator, Explorer, LS, and Mountaineer (150-pin PCM) with ABS-stability assist, measure DBA input at PCM harness connector and ground while applying and releasing the brake. For all others, using a DVOM, measure voltage between BPP circuit at PCM harness connector and chassis ground while applying and releasing brake pedal. If voltage does not cycle, repair open in BPP circuit to PCM. If voltage cycles, go to next step (Aviator, Explorer, LS, Mountaineer and Thunderbird), or replace PCM (all others).

  11. 11) Check For BPA Circuit Cycling

    Ensure PCM connectors are disconnected. Using a DVOM, measure voltage between BPA circuit at PCM harness connector and chassis ground while applying and releasing brake pedal. If voltage does not cycle, go to next step. If voltage cycles, go to step  15).

  12. 12) Check BPA Circuit For Open In Harness

    Disconnect BPA deactivator switch connector. Using a DVOM, measure resistance of BPA circuit between PCM harness connector and BPA deactivator switch harness connector. See Figure-Figure . See WIRING DIAGRAMS . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in BPA circuit between BPA switch and PCM.

  13. 13) Check BPA Deactivator Switch

    Using a DVOM, measure resistance between BPA deactivator switch terminals while applying and releasing brake pedal. With brake pedal applied, resistance should be more than 10 k/ohms. With brake pedal released, resistance should be less than 5 ohms. If resistance is as specified, repair VPWR circuit to BPA deactivator switch. If resistance is not as specified, replace BPA deactivator switch.
    14. NOTE: If BPA PID is not accessible with scan tool in this test step, go to step  11).

  14. 14) Check For PCM BPA PID Cycling
    Start engine and allow to idle. Using scan tool, access BPA PID from PID/DATA MONITOR & RECORD menu. Apply and release brake pedal several times while monitoring BPA PID. If BPA PID cycles ON and OFF, go to next step. If BPA PID does not cycle ON and OFF, go to step  11).

  15. 15) BPP & BPA Switch Rationality Check

    Reconnect all disconnected components. Clear DTCs. See CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Start engine and allow to idle. Apply and release brake pedal several times. Perform CONTINUOUS MEMORY SELF-TEST . If P1572 is still present, check for misadjusted BPP or BPA switch. Service as necessary. If DTC P1572 is no longer present, go to next step.

  16. 16) Check PCM For Reoccurring BPP DTCS

    Re-run KOER Self-test. Retrieve Continuous Memory DTCs. If DTC P0703 or P1703 is present, replace PCM. If DTC P0703 or P1703 is not present, test is complete.
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