Operational Checks
WORK SEQUENCE
- connect harness adapter vw 1315A/1 between differential pressure regulator and open harness connector
- connect meter US 1119 to harness adapter VW 1315A/1
- proceed with checks
COLD ACCELERATION ENRICHMENT, CHECKING
- remove harness connector from engine coolant temperature sensor (arrow) and leave open
- fully open throttle body (idle switch has no continuity)
- switch ON ignition
- remove intake air boot
- quickly lift sensor plate fully
^ current must briefly increase to greater than 110 mA, then drop to 80 - 110 mA
If NO
- check potentiometer and wiring circuit to control unit. (Terminals 14, 17 and 18 of control unit and 3, 2 and 1 of potentiometer)
If circuits OK
- replace control unit
AFTER-START AND WARM-UP ENRICHMENT, CHECKING
- remove fuel pump relay from relay panel
- remove connector from engine coolant temperature sensor and leave open
- ground ignition coil high tension wire from terminal 4 with jumper wire
- crank starter for three seconds and return ignition switch to ON position
- current must be greater than 120 mA for 30 - 60 seconds, then drop to 80 - 110 mA
If NO
- check for open circuit in wire between terminals 24 on control unit connector and 15a on starter
If OK
- check between control unit connector terminals 21 and 2,
If wiring OK
- replace control unit
STARTING ENRICHMENT, CHECKING
- insert "bridge" end of double adapter VW 1490 into open connector of engine coolant temperature sensor harness
- crank engine with starter for three seconds
^ current must be greater than 70 mA for first 1.5 seconds of starter operation
If NO
- check for open circuit in wire between terminals 24 on control unit connector and 15a on starter
If OK
- check between control unit connector terminals 21 and 2,
If wiring OK
- replace control unit
FULL THROTTLE ENRICHMENT, CHECKING
- insert -- end of double adapter VW 1490 into open connector of engine coolant temperature sensor harness
- unplug oxygen sensor
- switch ignition ON
- activate full throttle switch completely
^ current increases approx. 3 mA when switch is activated
If NO
- check full throttle switch
If switch OK
- check for open circuit in wiring between terminals 5 and 2 of control unit connector and full throttle switch
If wiring OK
- replace control unit
OXYGEN SENSOR CONTROL UNIT, CHECKING
- insert 17 end of double adapter VW 1490 into open connector of engine coolant temperature sensor harness
- unplug oxygen sensor connector
- switch ON ignition
- read differential pressure regulator current displayed on meter US 1119
^ current reading must correspond to above chart
Example:
^ 1,000 ft. above sea level should be approx. 8 - 12 mA
If NOT OK
- check altitude sensor
If OK
- ground male connector (green wire) of oxygen sensor lead
- read differential pressure regulator current displayed on US 1119
- current reading must increase approx. 10 mA above previous reading within 20 seconds
- remove oxygen sensor connection from ground
^ current reading must stabilize after approx. 10 seconds
If current readings NOT OK
- check circuit between terminal 8 of control unit connector and oxygen sensor. Repair if necessary, see current flow diagram
If OK
- check circuit between terminal 21 of control unit connector and engine coolant temperature sensor. Repair if necessary, see current flow diagram
If circuits OK
- replace control unit
DECELERATION FUEL SHUT-OFF, CHECKING
TEST CONDITIONS
- engine oil temperature min. 50°C (120°F)
- reconnect plug to engine coolant temperature sensor
- start engine and raise rpm above 2,000
- release throttle
- read differential pressure regulator current displayed on US 1119
^ current reading must briefly drop to negative value (-30 mA to -60 mA)
If NOT OK
- check for open idle switch circuit at terminals 2 and 13 of control unit connector
If circuit OK
^ replace control unit
ALTITUDE SENSOR, CHECKING
NOTE: Perform this check if differential pressure regulator current readings are found to be out of specifications based on altitude.
- remove harness connector from engine coolant temperature sensor and leave open
- remove fuel pump relay from fuse/relay panel
- switch US 4480/3 OFF
- plug US 4480/3 in place of fuel pump relay
- unplug connector from altitude sensor (upper arrow)
- switch US 4480/3 ON
- switch ignition ON
- read differential pressure regulator
- current reading must be 10 ± 2 mA
- connect jumper wire across terminals 1 and 2 on sensor plug
^ current reading must be approx. 11 - 14 mA
- remove jumper wire and connect across terminals 1 and 3 of sensor plug
- current reading must be approx. 0 - 4 mA
If current readings OK
- replace altitude sensor and adjust CO
If current readings NOT OK
- check for open circuit in wiring between altitude sensor and control unit connector, see current flow diagram
If wiring OK
- replace control unit