On Board Diagnosis System (OBD) - Display
89vw07SUBJECT:
On Board Diagnosis System (OBD)
GROUP
24
NUMBER
89-07 August 31, 1989
MODEL(S):
Golf w/Digifant II Jetta California only
Note
Also see Technical Information Group 90 # 89-02 for related information.
On Board Diagnosis system (OBD), display
The OBD light (installed on California Digifant II vehicles) may illuminate for two different reasons.
1. An actual fault (as identified by control unit criteria) exists in the emission control system.
2. There is no fault in the emission control system, but the diagnostic system is too sensitive, which consequently triggers the light.
Proceed with the following sequence
Identifying the stored fault code:
When components are displayed as faulty (via fault coding) perform the following checks first BEFORE replacing the component:
^ check the wiring using wiring diagrams 87-70 or 87-74
^ gently pull on the end of the wire where it goes into the ECU and on the other end where it goes into the component
^ check terminals for proper seating and crimping
^ check connector fit between the harness connector and the component
^ repair as necessary
Coolant temperature sensor, checking
^ check resistance at control unit harness connector, terminals 6 + 10
^ must be 2000 to 3000 ohms at 70~F
If infinite resistance (open)
^ check wiring between sensor and control unit using wiring diagram, repair as necessary
^ repeat measurement
If still NOT within specifications
^ replace coolant temperature sensor
Intake air temperature sensor, checking
^ check resistance at control unit harness connector terminals 6 + 9
^ must be 2000 to 3000 ohms at 70~F If infinite resistance (open)
^ check wiring between sensor and control unit using wiring diagram, repair as necessary
^ repeat measurement
If still NOT within specifications
^ replace intake air temperature sensor
Air flow sensor potentiometer, checking
^ check resistance at control unit harness connector terminals 6 + 17
^ must be 500 to 1000 ohms
^ check resistance at control unit harness connector terminals 17 + 21 by manually moving air flow sensor plate or by actuating starter motor
^ a change in resistance should be noticeable
If infinite resistance (open)
^ check wiring between sensor and control unit using wiring diagram, repair as necessary
^ repeat measurement
Note
Resistance must fluctuate when sensor plate is operated. Sensor plate should swing freely, without binding.
^ replace potentiometer if not within specifications
Knock sensor, checking
^ check knock sensor part number
^ correct part number is 034 905 377 A
CAUTION
Part numbers are for reference only. Always check with the parts department for the latest information.
If incorrect
^ replace with knock sensor of correct part number
^ check knock sensor torque
^ must be 20-25 N-m (15 to 18 ft.lb.) with engine cold
Oxygen sensor, checking
^ check oxygen sensor function with engine running and CO tester connected
^ disconnect and connect Oxygen sensor
^ observe response time while Oxygen sensor is in closed loop
^ replace sensor if non-functional or response time is too slow
Note
A correctly functioning Oxygen sensor will react immediately when disconnected and re-connected.
OBD light, canceling
^ test drive vehicle for at least 10 minutes
^ press and hold down rocker switch
^ switch ignition ON
^ continue depressing switch for about 15 seconds
^ switch ignition OFF
If the OBD light comes ON again after:
^ the system has been diagnosed as having no faults or
^ repairs have been performed to correct wiring or component failures or
^ it has been verified that there are no running problems or
^ incorrect emission values have been measured and correctly adjusted more
The customer should be advised:
1. That the diagnostic system is now in proper working order.
2. That the system was designed to preventatively sense temporary deviations in the air fuel mixture which are not malfunctions of the system but which are inherent in the normal operation of every vehicle.
3. That if the customer so desires, we will disconnect the OBD light temporarily with the understanding that the system will be restored whenever an improved system becomes available.
OBD light, disconnecting
Golf
^ remove blue/brown wire from connector T3d located near relay panel
^ tape end of wire with electrical tape Jetta
^ disconnect single connector T1b (20 gage white/red wire) behind the fuse/relay panel
Note
The OBD wire originates from the 32 pin harness connector and terminates in the 3 pin connector in plenum chamber.
Labor operation 9034 710
Diagnose and check 60 t.u.
warning light