Sensor and Control Check
Special tools and equipment
- Scan tool VAG 1551 or vehicle system tester VAG 1552 with cable VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram
Check conditions
- Exhaust system between catalyst and cylinder head must be free of leaks
- Coolant temperature must be at least 80 °C, See display group 04, display zone 3.
Functional check
- Connect scan tool VAG 1551 (VAG 1552). Start engine and select "Address word" 01 of engine control module. When doing this the engine must be running at idling speed.
(Connecting scan tool and selecting engine control module). Refer to "VAG 1551 Scan Tool" [1][2][3][4][5]Connecting VAG 1551 Scan Tool
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.
Indicated on display:
Read measured value block HELP
Input display group number XXX
- Press keys 0, 3 and 0 for "Display group number 30" and confirm entry with Q key.
Indicated on display: (1-4 = Display zones)
Read measured value block 30 ->
1 2 3 4
- Check Oxygen sensor control status before catalyst (display zone 1):
Specification: 1 1 1
Significance of 3 digit number block in display zone 1:
If the specification is not obtained:
- Check heated oxygen sensor before catalyst. Checking
If the specification is obtained:
- Change to display group 32 as follows:
- Press C key.
- Press keys 0, 3 and 2 for "Display group number 32" and confirm entry with Q key.
Indicated on display: (1-4 = Display zones)
Read measured value block 32 ->
1 2 3 4
- Check Oxygen sensor control learned values at idling speed (additive) in display zone 1.
Specification: -10.0 - 10.0 %
- Check Oxygen sensor control learned values at part load (multiplicative) in display zone 2.
Specification: -10.0 - 10.0 %
If the specification is not obtained:
Evaluating display group 32. Refer to "Scan Tool Testing/Measuring Value Blocks/Display Groups 30-49, 99, 107 (Oxygen Sensor Control)" Testing and Inspection
If the specification is obtained:
- Change to display group 33 as follows:
VAG 1551: Press key 3
VAG 1552: Press key up arrow
Indicated on display: (1-4 = Display zones)
Read measured value block 33 ->
1 2 3 4
- Observe Oxygen sensor control in display zone 1.
- The display must fluctuate at least 2% in the range -10.0 - 10.0 %
- Check Oxygen sensor voltage in display zone 2.
- The voltage must fluctuate at least 20 times per minute in range of 0 - 1.0 V.
If the display in display zone 2 remains constantly at a value:
- Continue check according to following table.
If the Oxygen sensor control in display zone 1 does not fluctuate as stated:
- Press -> key.
- Press keys 0 and 6 for "End data transfer" function and confirm input with Q key.
- Carry out road test and bum Oxygen sensors clean and repeat check.
Observe the valid safety precautions when carrying out a road test. Technician Safety Information
If the the specifications in display zone 1 are not obtained even after a test drive, or the value does not fluctuate by at least 2%:
- Replace Oxygen sensor before catalyst (G39).
Checking basic voltage
- Remove protective cover -arrows- and separate 4 pin connector (black) to Oxygen sensor before catalyst (G39).
- Connect multimeter with auxiliary cables from VAG 1594 to measure voltage at contacts 3 + 4 (connector to engine control module).
- Switch on ignition and measure basic voltage.
Specification: 0.40 - 0.50 V
- Switch off ignition.
If the specification is not obtained:
- Check Oxygen sensor wiring
If the specification is obtained:
- Replace Oxygen sensor before catalyst (G39).
Checking Oxygen sensor wiring
- Connect test box VAG 1598/31 to control module wiring harness. The engine control module remains disconnected.
- Check wiring between test box and 4-pin connector (to control module) for open circuit using wiring diagram.
Contact 3 + socket 51
Contact 4 + socket 70
Wire resistance: Max. 1.5 ohms
- Check the wiring at connector contacts 3 + 4 for short circuit to contacts 1 + 2.
If no wiring fault is detected:
- Replace Oxygen sensor before catalyst (G39).