Oxygen Sensor and Oxygen Sensor Control, Checking

Oxygen Sensor and Oxygen Sensor Control, Checking

Requirements
- engine coolant temperature 80°C (176°F) minimum
- idle adjustment OK
- no leaks in exhaust system between catalyst and cylinder head
- voltage supply for Oxygen sensor heater OK
- switch ignition OFF

For vehicles built up to 9-90:
- switch Fluke 83 multimeter to mA range
- disconnect differential pressure regulator (N 71) harness connector





- connect test adaptor VAG 1315A/1 between regulator and harness connector (arrows)
- connect multimeter to test adaptor VAG 1315A/1 using jumper leads from VW 1594 adaptor kit
- switch ignition ON
- control current polarity (90-110 mA) must be positive (+); if not, swap test connections
- start engine and let idle for 2 minutes minimum
- record control current





- clamp crank case housing breather hose 1
- control current must decrease





If NO

For vehicles built up to 7-90:
- disconnect OXS harness connector 1
- touch wire to control unit (arrow) for approx. 20 seconds
- touch ground (-) if necessary, using jumper leads from VW 1594 adaptor kit





For vehicles built after 8-90:
- disconnect OXS (4 pin) harness connector and OXS heater 1, mounted on right engine mount
- touch violet wire from control unit (arrow) to ground for approx. 20 seconds using jumper leads from VW 1594 adaptor kit

If control current changes
- replace OXS sensor (G 39)
- read and then erase Fault memory

If control current does not change
- perform Electrical Test Step 13 in Repair Group D2 and/or replace control unit (J 204)
- read and then erase Fault memory, see Repair Group D2 for additional information





For vehicles built after 10-90 starting with control unit:
49 States - 8A0 907 404
California - 893 907 404Q

- connect VAG 1551 Diagnostic Tester using VAG 1551/1 adaptor cable as follows
- connect VAG 1551/1 black connector to black diagnostic connector 1 in vehicle
- display must appear on tester

NOTE: If a display does not appear do not connect white connector. There is a problem with the vehicle power supply to the VAG 1551: Check using wiring diagram, repair or replace as necessary.

After display "V.A.G SELF-DIAGNOSIS:" appears
- connect white VAG 1551 connector to brown and/or white diagnostic connector 2 in vehicle
- start engine, and let idle
- press 1 to enter "rapid data transfer"
- press 0 and 1 to select engine electronics
- press Q button to enter input
- press --> key
- press 0 and 8 buttons to select function "read measurement block"
- press Q button to enter input
- display will appear as shown

Read measuring value block HELP
Input display group number X

- press 0 button twice to select "Display group 00"
- 0 display will appear as shown

Read measurement block Q
Input display group number 00

- press Q button to enter input
- display will appear as shown

Read measurement block -->
1 2 3 4 5 6 7 8 9 10

Continue with testing if the value displayed in channel 1 is less than 63 which corresponds to a coolant temperature of at least 80°C (176°F)
- read OXS signal value in channel 6
- display must fluctuate

If YES
- press --> button.
- press 0 and 6 button to select function "end output"
- press Q button to enter input





If display does NOT fluctuate
- disconnect OXS sensor (4-pin) and OXS heater harness connectors
- mounted on right engine mount (arrow)





- touch violet wire from control unit (arrow) to ground for approx. 20 seconds using jumper wires from VW 1594 adaptor kit
- value displayed in channel 6 must increase

If YES
- replace OXS sensor (G 39)
- read and then erase Fault memory

If display value does not increase

- perform Electrical Test Step 13 in Repair Group D2 and/or replace CIS-E Motronic control unit (J 204)
- read and then erase Fault memory