Brake On/Off (BOO) Switch

1994 PCED OBDI-A

SECTION 18A: Diesel Diagnosis — 7.3L DI Engine

K: Brake On/Off (BOO) Switch

K1 DIAGNOSTIC TROUBLE CODE (DTC) 536: VERIFY BRAKE WAS PRESSED

DTCs 536 indicate that when the brake pedal was depressed and released during the Key On Engine Running (KOER) Self-Test, the BOO signal did not cycle high and low.

Possible causes:

Brake pedal not depressed and released during the KOER Self-Test.
Brake pedal depressed during entire KOER Self-Test.
Open BOO/stoplamp circuit.
Short to GROUND or POWER.
Damaged brake switch.
Damaged Powertrain Control Module (PCM).

Was the brake pressed during the KOER Self-Test?

Note: If depressing the brake pedal does not allow you to enter the Brake ON/OFF (BOO) switch test, wait approximately 2 minutes for the system to cycle, then it will enter the test cycle. If there is a system fault, a Code 536 should be retrieved.

Yes	No
GO to K2.	RERUN KOER Self-Test. PRESS brake once during test.

K2 RABS WARNING LIGHT IS ON

Key on, engine off.

Does the rear anti-lock brake system (RABS) warning light come on and stay on?

Yes	No
REPAIR rear anti-lock brake system according to Section 06-09 of the F-Series Body/Chassis Service Manual.	GO to K3.

K3 CHECK OPERATION OF STOPLAMPS

Key on.
Check stoplamp operation.

Do stoplamps operate normally?

Yes	No, stoplamps never on	No, stoplamps always on
GO to K4.	GO to K5.	GO to K6.

K4 CHECK FOR BOO CIRCUIT CYCLING

Key off.
Disconnect powertrain control module (PCM). Inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box. Leave PCM disconnected.
DVOM on 20 volt scale.
Measure voltage between BOO Test Pin 92 and Test Pin 51 at the breakout box while depressing and releasing brake.

Does the voltage cycle?

Yes	No
REPLACE PCM. REMOVE breakout box. RERUN Scan Tool Diagnostic Test.	SERVICE open in BOO circuit between PCM and BOO connection to stoplamp circuit. RERUN Scan Tool Diagnostic Test.

K5 CHECK FOR POWER TO BRAKE SWITCH

Note: Using a 12V test lamp, verify integrity of related fuses in fuse panel and check condition of stoplamp bulbs.

Key off.
Disconnect brake switch (located on brake pedal).
Measure voltage between B+ input to brake switch and chassis ground.

Is voltage greater than 10 volts?

Yes	No
VERIFY operation of brake switch. If OK, SERVICE open circuit between brake switch and stoplamp ground. RECONNECT brake switch connector. RERUN Scan Tool Diagnostic Test.	SERVICE open B+ circuit to brake switch. RECONNECT brake switch connector. RERUN Scan Tool Diagnostic Test.

K6 VERIFY BRAKE SWITCH IS NOT ALWAYS CLOSED

Key off.
Brake switch disconnected.
Key on, engine off.

Are stoplamps still on?

Yes	No
GO to K7.	VERIFY proper installation of brake switch. If OK, REPLACE brake switch. RECONNECT harness connector. RERUN Scan Tool Diagnostic Test.

K7 CHECK FOR SHORT TO POWER IN PCM

Key off.
Brake switch disconnected.
Disconnect powertrain control module (PCM).
Key on, engine off.