Mixture Calibration Potentiometer: Testing and Inspection
CO potentiometer, checkingRequirement
- idle speed OK
- coolant temperature 80°C (176°F) minimum
- connect VAG 1551 Diagnostic tester
- start engine and let idle
- select Function "Read measuring value block"
or
- while observing VAG 1551 display, select the following functions in sequence
1 - Rapid data transfer
01 - Engine electronics
08 - Read measuring value block
- press keys 0 and 1 to select "Display group number 01"
- display will appear as shown
- press 0 key to acknowledge input
- channels will be displayed as shown
- observe display value in channel 2
Test A
- disconnect CO potentiometer harness connector
- display value: 250 minimum
If YES
- triggering of CO potentiometer (G 74) OK
- switch OFF ignition
- replace CO potentiometer assembly (G 74)
- includes intake air temperature sensor (G 42)
- activate Fault memory and then erase
- check idle and CO values, adjust if necessary
- displayed value must be 0 to 2
If NO
- CO potentiometer triggering (G 74) NOT OK
- switch OFF ignition
- reconnect CO potentiometer (G 74) harness connector
- eliminate short in wiring between control unit and ground using wiring diagram
If wiring OK
- replace control unit (J 169)
- activate Fault memory and then erase
Test B
- disconnect CO potentiometer harness connector (with intake air temperature sensor) and bridge terminals 1 and 3 of connector using jumper wires from VW 1594 adaptor kit
displayed value must be 0 to 2
If YES
- control unit triggering OK
- switch OFF ignition.
- replace CO potentiometer (G 74) assembly
- includes intake air temperature sensor (G 42)
- activate Fault memory and then erase
- check idle and CO values, adjust if necessary
- displayed value must be 250 minimum
If NO
- control unit triggering not OK
- switch OFF ignition
- reconnect CO potentiometer (G 74) harness connector
- determine open circuit and eliminate using wiring diagram
If wiring OK
- replace Digifant control unit (J 169)
- activate Fault memory and then erase