Parking Brake Applied (PBA) Switch

1996 PCED OBDI

SECTION 18: Diesel Diagnosis — 7.3L DI Engine

Q: Parking Brake Applied (PBA) Switch

Q1 DIAGNOSTIC TROUBLE CODE (DTC) 1536 OR NGS TESTER PID "PBA": DETERMINE CAUSE OF PBA NOT CHANGING STATES

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.

DTC 1536 is set when the PCM does not see a PBA state change during KOER.
Possible causes:

Low brake fluid.
Short to ground.
Short to B+.
Open circuit.

Confirm "Brake Warning" and "RABS" light are working during engine start mode (Bulb Check).

Are bulbs working?

Yes	No
GO to Q2.	SERVICE bulbs circuitry: Circuit 977 (P/W) (possible short to B+) and Circuit 640 (R/Y). REFER to Section 06-09A of the Body, Chassis Service Manual. CONFIRM fix with Bulb Check during start mode.

Q2 CHECK FOR BRAKE SYSTEM PROBLEM

Key on, engine off.
Parking brake fully off.

Are both "Brake Warning" and "RABS" lights ON?

Yes	No
SERVICE Brake System. REFER to Section 06-00 of the Body, Chassis Service Manual.	GO to Q3.

Q3 CHECK PID "PBA" WITH NGS TESTER

No PID transition indicates a PBA circuit failure.
Key on, engine off.
Cycle parking brake.

Does PID read ON only?

Yes	No
GO to Q4.	GO to Q6.

Q4 CHECK FOR PBA SWITCH FAILED CLOSED

Key on, engine off.
Parking brake fully up.
Unplug PBA switch.

Does PID go to OFF?

Yes	No
REPLACE PBA switch. CONFIRM fix with NGS Tester PID "PBA."	GO to Q5.

Q5 CHECK CIRCUIT 977 (P/W) FOR SHORT TO GROUND

(PBA switch unplugged)
Key off.
Unplug PCM.
Key on.
Check resistance between Circuit 977 (P/W) contact at PBA connector and chassis ground.

Is resistance less than 10,000 ohms?

Yes	No
SERVICE short to ground in Circuit 977 (P/W). REASSEMBLE system. CONFIRM fix with NGS Tester PID "PBA."	Short to ground is at PCM Pin 4. INSPECT PCM connector and PCM pins. SERVICE as necessary. REASSEMBLE system. GO to Q9.

Q6 CHECK PID "PBA"

Cycle parking brake.

Does PID read OFF only?

Yes	No
Open circuit. GO to Q7.	Fault may be intermittent. GO to Q10.

Q7 CHECK PBA SWITCH AND CIRCUIT LEAD FOR OPEN

(PBA switch unplugged)
Key on.
Jumper between PBA connector contact for Circuit 977 (P/W) and ground.
Check NGS Tester PID "PBA."

Does PID read ON?

Yes	No
REPLACE PBA switch. REASSEMBLE system. CONFIRM fix with NGS Tester PID "PBA."	GO to Q8.

Q8 CHECK CIRCUIT 977 (P/W) LEAD FOR OPEN

(PBA switch unplugged)
Key off.
Unplug PCM.
Inspect 104 pin connector and repair as required.
Attach 104 pin breakout box.
Leave PCM disconnected.
Key on.
Check voltage between Test Pin 4 and chassis ground.

Is B+ present?

Yes	No
Circuit 977 (P/W) is OK. Open is at PCM Pin 4. INSPECT PCM connector and pins and REPAIR as required. REASSEMBLE system. GO to Q9.	SERVICE open in Circuit 162 (LG/R), DRL jumper, or Circuit 977 (P/W) PBA switch lead. REASSEMBLE system. CONFIRM fix with NGS Tester PID "PBA."

Q9 CONFIRM PCM FAULT

Key on, engine off.
Check NGS Tester PID "PBA."
Cycle parking brake.

Does PID switch between ON and OFF?

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

Q10 CHECK FOR INTERMITTENT SHORT TO GROUND

(PBA switch unplugged)
Key on.
Confirm that NGS Tester PID "PBA" shows OFF.
Wiggle connectors and wires while watching PBA on NGS Tester.

Does PID switch between OFF and ON?

Yes	No
SERVICE circuitry at point of intermittent. REASSEMBLE system. CONFIRM fix with NGS Tester PID "PBA."	GO to Q11.

Q11 CHECK FOR INTERMITTENT OPEN

Engage parking brake.
Confirm that NGS Tester PID "PBA" shows ON.
Wiggle connector and wires while watching PBA on NGS Tester.

Does PID switch between ON and OFF?

Yes	No
SERVICE circuitry at point of intermittent open. REASSEMBLE system. CONFIRM fix with NGS Tester PID "PBA." RUN NGS Tester KOER On-Demand Self Test.	Intermittent not detected. REASSEMBLE system. CONFIRM fix with NGS Tester PID "PBA." RUN NGS Tester KOER On-Demand Self Test.