Test FB: Brake Pressure Applied Switch: Testing

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 2002 Ford RV Cutaway, 2002 Ford Pickup, 2002 Ford F550 Super Duty, 2002 Ford F450 Super Duty, and 2002 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: For additional testing information, see DIAGNOSTIC AIDS .

NOTE: When performing KOER SWITCH TEST, wait 5 seconds after pressing "Trigger" to start test before running through driver operated controls. Test may take up to 5 minutes to complete.

NOTE: No BPA PID transition indicates a BPA circuit fault.

1) DTC P0571: Check BPA PID
DTC P0571 indicates BPA switch circuit malfunction. Possible causes for this fault are:
- BPA Circuit Open, Or Shorted To Ground Or PWR
- BPA PWR Circuit Open Or Shorted To Ground
- Faulty BPA Switch
- Faulty Harness Connector
- Faulty PCM
Connect scan tool to Data Link Connector (DLC). Turn ignition on. Using scan tool, access BPA PID from PID/DATA MONITOR & RECORD menu. While observing BPA PID reading, firmly apply then release brake pedal. If BPA PID reading indicates ON only, leave scan tool in PID/DATA MONITOR & RECORD mode and go to next step. If BPA PID reading does not indicate ON only, leave ignition on, scan tool in PID/DATA MONITOR & RECORD mode and go to step 4).

2) Check BPA Switch

Turn ignition off. Disconnect BPA switch connector located above brake pedal. If BPA PID changes to OFF when switch is disconnected, replace BPA switch. Clear DTCs and retest. If BPA PID does not change to OFF when switch is disconnected, go to next step.

3) Check For Short To Voltage In Switch To PCM Circuit

Turn ignition off. Disconnect PCM connector. PCM is located in left rear of engine compartment, near brake master cylinder. Turn ignition on. Using DVOM, check for battery voltage between chassis ground and Red/Light Green wire (Econoline) or Black/Yellow wire (all others) at BPA switch harness connector. See Figure-Figure . If battery voltage is present, repair short to voltage in Red/Light Green wire or Black/Yellow wire between PCM terminal No. 31 and BPA switch. If battery voltage is not present, inspect PCM terminal No. 31 for short to voltage. Check for damaged pin, corrosion or loose wire. Repair as necessary.

4) Check BPA PID

While observing BPA PID, apply and release brake pedal several times. If BPA PID reading indicates OFF only, go to next step. If BPA PID reading cycles between ON and OFF, fault may be intermittent. Leave scan tool connected to DLC and go to step 12).

5) Check Fuse

Remove and inspect BPA PWR feed circuit fuse. Refer to appropriate fuse in illustrations. See Figure-Figure . If BPA PWR feed circuit fuse is okay, go to step 8). If BPA PWR feed circuit fuse is blown, replace fuse. If fuse blows again, remove fuse and go to next step.

6) Check BPA PWR Feed Circuit For Short To Ground

Disconnect BPA switch connector. Ensure BPA PWR circuit fuse is removed. Using DVOM, measure resistance between chassis ground and appropriate PWR feed circuit at BPA switch harness connector. For proper wire colors, refer to BPA PWR FEED CIRCUIT WIRE IDENTIFICATION table. See Figure-Figure . If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in appropriate BPA PWR feed circuit. Restore vehicle, clear DTCs and retest.

BPA PWR FEED CIRCUIT WIRE IDENTIFICATION

Application	Wire Color
Econoline	Light Green/Red
Excursion & F250-550	Red
F650-750	Tan/Black

7) Check BPA Circuit For Short To Ground

Disconnect PCM connector. PCM is located in left rear of engine compartment, near brake master cylinder. Repair connector as necessary. Install Rotunda Breakout Box (014-00950), leaving PCM disconnected. Using DVOM, measure resistance between chassis ground and test pin No. 31 at breakout box. If resistance is more than 10 k/ohms, leave breakout box installed and go to step 19). If resistance is 10 k/ohms or less, repair short to ground in Red/Light Green wire (Econoline) or Black/Yellow wire (all others) between PCM and BPA switch. Clear DTCs and retest.

NOTE: On F650-750 with air brakes, perform the following test steps on both BPA switches and circuits. See Figure. Perform step 8) first with BPA switch No. 1 jumpered and BPA switch No. 2 disconnected. Then reconnect BPA switch No. 2, disconnect BPA switch No. 1 and repeat this test jumpering BPA switch No. 2.

8) Check For Open BPA Switch
Reinstall BPA PWR feed circuit fuse. Disconnect BPA switch harness connector. Turn ignition on. Connect a jumper wire between BPA switch harness connector terminals. Using scan tool, access BPA PID from PID/DATA MONITOR & RECORD menu. If BPA PID reading indicates ON, replace BPA switch. Clear DTCs and retest. If BPA PID reading indicates OFF, disconnect jumper wire and go to next step.

9) Check BPA PWR Feed Circuit For Open

Turn ignition off. Using DVOM, measure resistance of BPA PWR feed circuit between output side of BPA PWR circuit fuse and BPA switch harness connector. For proper wire colors, refer to BPA PWR FEED CIRCUIT WIRE IDENTIFICATION table. See Figure-Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in appropriate BPA PWR feed circuit. Restore vehicle, clear DTCs and retest.

10) Check BPA Circuit For Open

Disconnect PCM connector. PCM is located in left rear of engine compartment, near brake master cylinder. Repair connector as necessary. Install Rotunda Breakout Box (014-00950), leaving PCM disconnected. Using DVOM, measure resistance of Red/Light Green wire (Econoline) or Black/Yellow wire (all others) between BPA switch harness connector and test pin No. 31 at breakout box. If resistance is less than 5 ohms, inspect PCM terminal No. 31 for open. Check for damaged pin, corrosion or loose wire. Repair as necessary, then go to next step. If resistance is 5 ohms or more, repair open in Red/Light Green wire or Black/Yellow wire between PCM and BPA switch. Clear DTCs and retest.

11) Confirm PCM Fault

Disconnect breakout box. Reconnect all components and reinstall BPA PWR circuit fuse. Turn ignition on. Using scan tool, access BPA PID from PID/DATA MONITOR & RECORD menu. While observing BPA PID reading, firmly apply then release brake pedal several times. If BPA PID reading cycles between ON and OFF, system is okay. Testing is complete. If BPA PID reading does not cycle between ON and OFF, replace PCM. Clear DTCs and retest.

12) Check For Intermittent Open Or Short

Turn ignition off. Disconnect BPA switch. Turn ignition on. Connect a jumper wire between both BPA switch harness connector terminals. See Figure-Figure . Using scan tool, access BPA PID from PID/DATA MONITOR & RECORD menu. BPA PID reading should indicate ON. While observing BPA PID, wiggle and bend small sections of wiring harness working from BPA switch toward PCM. BPA PID reading changes to OFF if fault is present. If fault is indicated, isolate fault and repair as necessary. Clear DTCs and retest. If no fault is indicated, leave scan tool connected to DLC and go to next step.

13) Check For Intermittent Short To Voltage

Turn ignition off. Ensure jumper wire is still connected. Remove BPA PWR circuit fuse. Turn ignition on. Using scan tool, access BPA PID from PID/DATA MONITOR & RECORD menu. BPA PID should indicate OFF. While observing BPA PID, wiggle and bend small sections of wiring harness working from BPA switch toward PCM. BPA PID reading changes to ON if fault is present. If fault is indicated, isolate short to voltage and repair as necessary. Reinstall fuse, clear DTCs and retest. If no fault is indicated, system is okay at this time. Reinstall fuse, clear DTCs and retest.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 13) to step 19). No test procedures have been omitted.

19) Check PCM For Internal Short

Connect PCM connector to breakout box. Using DVOM, measure resistance between test pin No. 31 and test pins No. 25, 76, 77 and 103 at breakout box. If all resistances are more than 10 k/ohms, no concern is indicated at this time. Replace fuse, clear DTCs and retest. If any resistance is 10 k/ohms or less, replace PCM. Reinstall fuse, clear DTCs and retest.