FixVault

Stop Light Switch: Diagnosis/Troubleshooting

DIAGNOSIS/TROUBLESHOOTING - FAULT CODE 4340

Work instruction Display OK If not OK
1 Visual inspection
  • Check adjustment of stop light switch
  • Check brake lights
Step 2
  • Readjust stop light switch, replace if necessary
  • Repair brake lights
End
2 Check stop light input signals in control unit
  • In the Porsche System Tester II 9588 under menu item Input signals select the items Brake light and Brake pedal
  • Brake pedal released
Tester display:
  • Brake light off
  • Brake not actuated
Step 3
  • Observe tester display and slowly actuate brake pedal
Tester display:
  • Brake light off
  • Brake pedal actuated
Step 3
  • Continue to observe tester display and slowly actuate brake pedal again
  • Brake light on
  • Brake pedal actuated
Step 9
Step 3
3 Check stop light switch
  • Remove stop light switch
  • Measure resistance between pin 1 and pin 4
  Step 8
  • Stop light switch actuated
  • Measure resistance between pin 1 and pin 4
< 5
  • Stop light switch actuated
  • Measure resistance between pin 1 and 2
 
  • Release stop light switch
  • Measure resistance between pin 1 and 2
< 5
 
Step 4
4 Check break-contact circuit for short circuit to B+
  • Ignition off
  • Install stop light switch and connect plug
  • Pull plug off PSM control unit
  • Ignition on
  • Brake pedal actuated
  • Measure voltage between pin 37 of PSM control unit plug and ground
< 0.3 V
 
Step 5
5 Check break-contact circuit for open circuit
  • Ignition on
  • Brake pedal not actuated
  • Measure voltage between pin 37 of PSM control unit plug and ground
> 11 V
 
Step 6
Open circuit between pin 37 of PSM control unit and pin 4 of stop light switch
 
Repair wiring harness
 
End
6 Check make-contact circuit for short circuit to B+
  • Ignition on
  • Brake pedal not actuated
  • Measure voltage between pin 32 of PSM control unit plug and ground
< 0.3 V
 
Step 7
Short circuit to B+ between pin 32 of PSM control unit and pin 2 of stop light switch
 
Repair wiring harness
 
End
7 Check make-contact circuit for open circuit
  • Ignition on
  • Brake pedal actuated
  • Measure voltage between pin 32 of PSM control unit plug and ground
> 11 V
 
Step 9
Open circuit between pin 32 of PSM control unit and pin 2 of stop light switch
 
Repair wiring harness
 
End
8
  • Replace stop light switch
End
9
  • Replace PSM control unit
End