Brake Lamp Switch

1997 PCED OBDII-Diesel

SECTION 5C: Pinpoint Tests

K: Brake Lamp Switch

K1 DIAGNOSTIC TROUBLE CODE (DTC) P0703: CHECK PID BOO 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 BOO circuit failure.
Key on, engine off.
Firmly cycle brake pedal.

Does PID read ON only?

Yes	No
GO to K2.	GO to K4.

K2 CHECK FOR BOO SWITCH FAILED CLOSED

Key on, engine off.
Unplug brake lamp switch.

Does PID go to OFF?

Yes	No
REPLACE brake lamp switch. CONFIRM fix with NGS Tester PID BOO and with stoplamp operation.	GO to K3.

K3 CHECK FOR SHORT TO B+ IN CIRCUIT 511 (LG)

Brake lamp switch unplugged.
Key off.
Unplug PCM.
Key on.
Check voltage between Circuit 511 (LG) brake lamp switch connector contact and chassis ground.

Is B+ present?

Yes	No
SERVICE short to B+ in Circuit 511 (LG). REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO and with stoplamp operation.	Short to B+ is at Pin 92 in PCM. INSPECT PCM connector and pins. SERVICE as necessary. REASSEMBLE system. GO to K11.

K4 CHECK PID BOO

Does PID read OFF only?

Yes	No
F-Series, GO to K5. Econoline, GO to K6.	Fault may be intermittent. GO to K13.

K5 CHECK FUSE 13 (15 AMP)

Check Fuse 13 (15 amp) in IP fuse panel.

Is Fuse 13 OK?

Yes	No
LOOK for open circuit. GO to K9.	THROW away fuse. LOOK for short to ground. GO to K7.

K6 CHECK FUSE 1 (15 AMP)

Check Fuse 1 (15 amp) in IP fuse panel.

Is Fuse 1 OK?

Yes	No
GO to K9.	THROW away fuse. LOOK for possible short to ground. GO to K7.

K7 CHECK CIRCUIT 383 (R/W) AND 10 (LG/R) FOR SHORT TO GROUND

Brake lamp switch unplugged.
Check resistance between circuit connector contact at brake lamp switch connector and chassis ground.

Is resistance less than 10,000 ohms?

Yes	No
SERVICE short to ground in Circuit 383 (R/W) or 10 (LG/R). REPLACE Fuse 13 (15A). REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO and with stoplamp operation.	GO to K8.

K8 CHECK CIRCUIT 511 (LG) FOR SHORT TO GROUND

Brake lamp switch unplugged.
Key off.
Unplug PCM.
Key on.
Check resistance between Circuit 511 (LG) contact at brake lamp switch connector and chassis ground.

Is resistance less than 10,000 ohms?

Yes	No
SERVICE short to ground in Circuit 511 (LG). REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO and with stoplamp operation.	Short to ground is at PCM Pin 92. INSPECT PCM connector and PCM pins. SERVICE as necessary. REASSEMBLE system. GO to K12.

K9 CHECK CIRCUITS 383 (R/W) AND 10 (LG/R) FOR OPEN

Brake lamp switch unplugged.
Fuse 13 unplugged.
Check resistance between circuit connector contact at brake lamp switch connector and fuse contact for Circuit 383 (R/W).

Is resistance less than 5 ohms?

Yes	No
Circuits 383 (R/W) and 10 (LG/R) are OK. GO to K10.	SERVICE open in Circuit 383 (R/W) or 10 (LG/R). REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO.

K10 CHECK BOO SWITCH FOR OPEN

Brake lamp switch unplugged.
Key on.
Jumper between brake lamp switch connector contacts for Circuits 511 (LG) and 10 (LG/R).
Check NGS Tester PID BOO.

Does PID read ON?

Yes	No
REPLACE brake lamp switch. REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO.	GO to K11.

K11 CHECK CIRCUIT 511 (LG) FOR OPEN

Brake lamp switch unplugged.
Remove jumper between brake lamp switch connector contacts for Circuits 511 (LG) and 10 (LG/R).
Key off.
Unplug PCM.
Inspect 104-pin connector and repair as required.
Attach 104-pin breakout box.
Leave PCM disconnected.
Key on.
Check resistance between Test Pin 92 and brake lamp switch connector contact for Circuit 511 (LG).

Is resistance less than 5 ohms?

Yes	No
Circuit 511 (LG) is OK. Open is at PCM Pin 92. INSPECT PCM connector and pins and REPAIR as required. REASSEMBLE system. GO to K12.	SERVICE open in Circuit 511 (LG). REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO and stoplamp operation.

K12 CONFIRM PCM FAULT

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

Does PID switch between ON and OFF?

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

K13 CHECKS FOR INTERMITTENT OPEN OR SHORT

Brake lamp switch unplugged.
Key on.
Jumper between brake lamp switch connector contacts for Circuits 511 (LG) and 10 (LG/R).
Confirm that NGS Tester PID BOO shows ON and that stoplamps are on.
Wiggle connectors and wires while watching BOO PID on NGS Tester and stoplamps.

Does PID switch between ON and OFF?

Yes	No
SERVICE circuitry at point of intermittent. REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO.	GO to K14.

K14 CHECK FOR INTERMITTENT SHORT TO B+

Brake lamp switch unplugged.
Remove fuse.
Jumper between brake lamp switch connector contacts for Circuits 511 (LG) and 10 (LG/R).
Confirm that NGS Tester PID BOO shows OFF and that stoplamps are off.
Wiggle connector and wires while watching BOO PID on NGS Tester and stoplamps.

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 BOO. RUN NGS Tester self test.	Intermittent not detected. REASSEMBLE system. CONFIRM fix with NGS Tester PID BOO. RUN NGS Tester self test.