Computers and Control Systems: Testing and Inspection

Ensure no exhaust leaks are present between catalytic converter and cylinder head. Check if voltage supply for oxygen sensor heater is correct. If satisfactory, proceed with further diagnosis as follows:
1. Ensure battery voltage is correct and all ground connections are satisfactory.
2. Ensure air conditioning is off.
3. On Corrado models, fuses 16, 18 and 21 and on all other models, fuses 3, 5 and 18 are satisfactory.
4. Install scan tool No. VAG 1551 or equivalent, as follows:
a. Remove shifter tunnel cover, then connect black connector to black test connector.
b. Connect white connector to white test connector.
c. Blue connector is not used.
5. Start engine and allow to idle.
6. Select ``Read measuring value block,'' then select the following in order:
a. 1-``Rapid data transfer.''
b. 01-``Engine electronics.''
c. 08-``Read measuring value block''
d. Press Q key to enter input.
e. Continue only after the digit in channel 3 is less than 11. (Corresponding to coolant temperature greater than 176°F).
7. Let engine idle for two more minutes.
8. Read display value in channel 5 (Oxygen sensor signal) as follows:
a. If display is over 14, oxygen sensor is OK.
b. If display is 0--5, there is a short circuit to positive in wiring between oxygen sensor and control unit. Perform the following test:
1. Disconnect oxygen sensor/heater harness connector. Display should be 164--168. If correct, oxygen sensor control is OK and replace oxygen sensor
2. If not within limits, turn off ignition and check wiring for short circuit to control unit.
3. If wiring is OK, replace Digifant control unit, then activate trouble code memory and erase.
c. If display is over 164--168, there is a open circuit in wiring between oxygen sensor and control board. Proceed with the following test:
1. Disconnect oxygen sensor/heater harness connector.
2. Touch violet wire from Digifant control unit to ground using jumper from part VW 1594 adapter kit. Display value must read a minimum of 230. If correct, oxygen sensor control is OK and replace oxygen sensor.
3. If not within limits, oxygen sensor control is faulty, turn off ignition and check wiring for open circuit to control unit. repair or replace as necessary.
4. If wiring is OK, replace Digifant control unit, then activate and clear trouble code memory as described in the ``Computerized Engine Controls'' section.
d. If display is minimum 230, there is a short circuit to ground in wiring between oxygen sensor and control unit. Proceed as follows:
1. Disconnect oxygen sensor/heater harness connector. Display must be 164--168, if correct, turn off ignition and replace oxygen sensor.
2. If not within limits, oxygen sensor control is faulty. Turn off ignition.
3. Check wiring for short circuit between control unit and ground.
4. If wiring is OK, replace Digifant control unit, then activate and clear trouble code memory.