Brake Pressure Applied (BPA) Switch

1997 PCED OBDII-Diesel

SECTION 5C: Pinpoint Tests

P: Brake Pressure Applied (BPA) Switch

P1 DIAGNOSTIC TROUBLE CODE (DTC) P0571: CHECK PID BPA WITH NGS TESTER

Note: When performing KOER switch test, wait five seconds after pressing the trigger to start the test before running through the driver operated controls. The test may also take up to five minutes to complete.

No PID transition indicates a BPA circuit failure.
Key on, engine off.
Cycle brake pedal firmly.

Does PID read ON only?

Yes	No
GO to P2.	GO to P5.

P2 CHECK FOR BPA SWITCH FAILED CLOSED

Key on, engine off.
Unplug BPA switch.

Does PID go to OFF?

Yes	No
REPLACE BPA switch. CONFIRM fix with NGS Tester PID BPA.	F-Series, GO to P3. Econoline, GO to P4.

P3 CHECK FOR SHORT TO B+ IN CIRCUIT 307 (BK/Y)

BPA switch unplugged.
Key off.
Unplug PCM.
Key on.
Measure voltage between Circuit 307 (BK/Y) BPA connector contact and chassis ground.

Is B+ present?

Yes	No
SERVICE short to B+ in Circuit 307 (BK/Y). REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.	Short to B+ is at Pin 31 in PCM. INSPECT PCM connector and pins. SERVICE as necessary. REASSEMBLE system. GO to P11.

P4 CHECK FOR SHORT TO B+ IN CIRCUIT 810 (R/LG)

BPA switch unplugged.
Key off.
Unplug PCM.
Key on.
Measure voltage between Circuit 810 (R/LG) at BPA connector and chassis ground.

Is B+ present?

Yes	No
SERVICE short to B+ in Circuit 810 (R/LG). REASSEMBLE and RETEST.	REPLACE PCM. REASSEMBLE and RETEST.

P5 CHECK PID BPA

Cycle brake pedal firmly.

Does PID read OFF only?

Yes	No
F-Series GO to P6, Econoline GO to P7.	Fault may be intermittent. GO to P14.

P6 CHECK FUSE 5 (15 AMP)

Check fuse 5 (15 amp) in power distribution box.

Is fuse 5 blown?

Yes	No
REPLACE fuse. If fuse blows again, GO to P8.	LOOK for open circuit. GO to P10.

P7 CHECK FUSE 1 (15 AMP)

Check fuse 1 (15 amp) in power distribution box.

Is fuse 1 blown?

Yes	No
REPLACE fuse. If fuse blows again, GO to P19.	GO to P16.

P8 CHECK CIRCUIT 298 (P/O) FOR SHORT TO GROUND

BPA switch unplugged.
Measure resistance between Circuit 298 (P/O) connector contact at BPA connector and chassis ground.

Is resistance greater than 10,000 ohms?

Yes	No
GO to P9.	SERVICE short to ground in Circuit 298 (P/O). REPLACE fuse. REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.

P9 CHECK CIRCUIT 307 (BK/Y) FOR SHORT TO GROUND

BPA switch unplugged.
Key off.
Unplug PCM.
Key on.
Measure resistance between Circuit 307 (BK/Y) contact at BPA connector and chassis ground.

Is resistance greater than 10,000 ohms?

Yes	No
GO to P21.	SERVICE short to ground in Circuit 307 (BK/Y). REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.

P10 CHECK BPA SWITCH FOR OPEN

BPA switch unplugged
Key on.
Jumper between BPA connector contacts for Circuits 307 (BK/Y) and 298 (P/O) (two middle pins).
Check NGS Tester PID BPA.

Does PID read ON?

Yes	No
REPLACE BPA switch. REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.	GO to P11.

P11 CHECK CIRCUIT 298 (P/O) FOR OPEN

BPA switch unplugged
Key off.
Measure resistance between Circuit 298 (P/O) connector contact at BPA connector and contact for Fuse 5.

Is the resistance less than 5 ohms?

Yes	No
Circuit 298 (P/O) is OK. GO to P12.	SERVICE open in Circuit 298 (P/O). REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.

P12 CHECK CIRCUIT 307 (BK/Y) FOR OPEN

BPA switch unplugged.
Remove jumper between BPA connector contacts for Circuits 307 (BK/Y) and 298 (P/O) (two middle pins).
Key off.
Unplug PCM.
Inspect 104-pin connector and repair as required.
Attach 104-pin breakout box.
Leave PCM disconnected.
Measure resistance between Test Pin 31 and BPA contact for Circuit 307 (BK/Y).

Is resistance less than 5 ohms?

Yes	No
Circuit 307 (BK/Y) is OK. Open is at PCM Pin 31. INSPECT PCM connector and pins and REPAIR as required. REASSEMBLE system. GO to P13.	SERVICE open in Circuit 307 (BK/Y). REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.

P13 CONFIRM PCM FAULT

Key on, engine off.
Check NGS Tester PID BPA.

Does PID switch between ON and OFF?

Yes	No
System is OK.	REPLACE PCM. CONFIRM fix with NGS Tester PID BPA. RUN self test.

P14 CHECKS FOR INTERMITTENT OPEN OR SHORT

BPA switch unplugged.
Key on.
Jumper between BPA connector contacts for Circuits 307 (BK/Y) and 298 (P/O) (two middle pins).
Confirm that NGS Tester PID BPA shows ON.
Wiggle connectors and wires while watching BPA on NGS Tester.

Does PID switch between ON and OFF?

Yes	No
SERVICE circuitry at point of intermittent. REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA.	GO to P15.

P15 CHECK FOR INTERMITTENT SHORT TO B+

BPA switch unplugged.
Remove Fuse 5 (15 amp).
Jumper between BPA connector contacts for Circuits 307 (BK/Y) and 298 (P/O) (two middle pins).
Confirm that NGS Tester PID BPA shows OFF.
Wiggle connector and wires while watching BPA on NGS Tester.

Does PID switch between OFF and ON?

Yes	No
SERVICE circuitry at point of intermittent contact with B+ source. INSTALL fuse. REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA. Run self test.	Intermittent not detected. REASSEMBLE system. CONFIRM fix with NGS Tester PID BPA. RUN self test.

P16 CHECK CIRCUIT 10 (LG/R) FOR OPEN

BPA switch unplugged.
Key off.
Measure resistance between Circuit 10 (LG/R) at BPA connector to the non-power side of Fuse 1.

Is resistance less than 5 ohms?

Yes	No
GO to P17.	SERVICE open in Circuit 10 (LG/R). RETEST system.

P17 CHECK BPA SWITCH FOR OPEN

Reinstall Fuse 1.
BPA switch unplugged.
Key on.
Jumper between BPA connector Circuits 10 (LG/R) and 810 (R/LG).
Check NGS Tester PID BPA.

Does PID read ON?

Yes	No
REPLACE faulty BPA switch. RETEST.	GO to P18.

P18 CHECK CIRCUIT 810 (R/LG) FOR OPEN

BPA switch unplugged.
Remove jumper from BPA connector.
Key off.
Disconnect PCM. Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Repair as necessary.
Install breakout box, leave PCM disconnected.
Measure resistance between Pin 31 and Circuit 810 (R/LG) at BPA connector.

Is resistance less than 5 ohms?

Yes	No
REPLACE PCM. RETEST system.	SERVICE open in Circuit 810 (R/LG). RETEST.

P19 CHECK CIRCUIT 10 (LG/R) FOR SHORT TO GROUND

BPA switch unplugged
Fuse 1 removed.
Measure resistance between Circuit 10 (LG/R) at BPA connector to ground.

Is resistance greater than 10,000 ohms?

Yes	No
GO to P20.	SERVICE short to ground in Circuit 10 (LG/R). REPLACE fuse. RETEST.

P20 CHECK CIRCUIT 810 (R/LG) FOR SHORT TO GROUND

BPA switch unplugged.
Fuse 1 removed.
Key off.
Disconnect PCM.
Measure resistance between Circuit 810 (R/LG) and ground.

Is resistance greater than 10,000 ohms?

Yes	No
GO to P21.	REPAIR short to ground in Circuit 810 (R/LG).

P21 PCM INTERNAL SHORT CHECK

BPA connector unplugged.
Install PCM to breakout box.
Measure resistance from Pin 31 to Pins 25, 76, 77 and 103.

Is resistance greater than 10,000 ohms?

Yes	No
Unable to identify short condition. REPLACE fuse and REASSEMBLE system.	REPLACE shorted PCM. RETEST.