Test sequence

• Connect VAG1551 or VAG1552 scan tool, see VAG1551 SCAN TOOL (ST), CONNECTING .

• Switch ignition on.
• Press buttons -0- and -1- to insert the "Engine Electronics" address word 01.

Indicated on display

Fig 1: Scan Tool Display - Checking Brake Light Switch And Brake Vacuum Vent Valve Switch (1 Of 5)

• Press buttons -0- and -8- to select "Read Measuring Value Block" function 08.
• Press -Q- button to confirm input.

Indicated on display

Fig 2: Scan Tool Display - Checking Brake Light Switch And Brake Vacuum Vent Valve Switch (2 Of 5)

• Press buttons -0-, -0- and -6- to input display group no. 6 (006).
• Press -Q- button to confirm input.
• Check value in display field 2.

  Specified display: 0 0 0

  Fig 3: Scan Tool Display - Checking Brake Light Switch And Brake Vacuum Vent Valve Switch (3 Of 5)

  
  • Center display element = Brake vacuum vent valve switch
  • Right display element = Brake light switch
• Press brake pedal slowly.

  Specified display: 0 1 1

  Fig 4: Scan Tool Display - Checking Brake Light Switch And Brake Vacuum Vent Valve Switch (4 Of 5)

  

• Release brake pedal slowly into rest position again

  Both display elements must change from "1" to "0" again.

  Fig 5: Scan Tool Display - Checking Brake Light Switch And Brake Vacuum Vent Valve Switch (5 Of 5)

  

If one or both elements do not change:

• Adjust brake vacuum vent valve switch activation point by turning switch.
• Adjust brake light switch activation point by moving plunger.

If center display element does not change:

• Press --> button.
• Press buttons -0- and -6- to select "End Output" function 06, and press -Q- button to confirm input.
• Switch ignition off.
• Disconnect harness connector from brake vacuum vent valve switch -1-.
  Fig 6: Disconnecting Harness Connector From Brake Vacuum Vent Valve Switch

  
• Measure resistance across switch terminals.

  Specifications:

  • Brake pedal not depressed: less than 10 ohms (ohm)
  • Brake pedal depressed: (no continuity)

If resistance is not as specified:

• Replace brake vacuum vent valve switch -F47-.

• Display readiness code, see READINESS CODE, DISPLAYING .

If DTC memory was erased:

• Create readiness code again, see READINESS CODE, SETTING (UP TO M.Y. 1997) .

If resistance values are OK:

• Connect VAG1598/18 test box to Diesel DFI ECM connector.
  Fig 7: Connecting VAG1598/18 Test Box To Diesel DFI ECM Connector

  
• Check wiring for open circuit between test box and harness connector, using wiring diagrams:
  • Terminal 1 and test box socket 20. See Fig 8 .
  • Terminal 2 and test box socket 33
  • Wire resistance: max. 1.5 ohms (ohm)
Fig 8: Checking Wiring For Open Circuit Between Test Box And Harness Connector

• Check wiring for short circuit between connector terminals.

  Specification: INFINITY ohm (no continuity)

If the right display element in display field 2 (brake light switch) does not change:

• Press --> button.
• Press buttons -0- and -6- to select "End Output" function 06, and press -Q- button to confirm input.
• Switch ignition off.
• Switch multimeter to 20 volt range.
• Connect multimeter using adapters from VW1594 connector test kit, and check voltage between test box sockets 1 and 44.

  Specifications:

  • Brake pedal not depressed: 0 (no voltage)
  • Brake pedal depressed: approx. battery voltage (B+)

If there is no voltage:

• Check brake lights.

If the brake lights are OK:

• Check wiring to brake light switch for open or short circuit, using wiring diagrams.

If the brake lights do not come on:

• Replace brake light switch -F-.
• Display readiness code, see READINESS CODE, DISPLAYING .

If DTC memory was erased:

• Create readiness code again, see READINESS CODE, SETTING (UP TO M.Y. 1997) .