Oxygen Sensor: Testing and Inspection
CHECKING HEATED OXYGEN SENSORSpecial Tools
^ Scan Tool (ST) VAG 1551 using adaptor cable VAG 1551/1.
Requirements
^ Idle speed check OK.
^ Exhaust system must be leak tight between the three-way catalytic converter and the cylinder head.
Procedure
- Connect VAG 1551 Scan Tool.
- Start engine and let idle.
- Select function 08 "Read measurement block" (display group number 01).
^ Display will appear as shown: (1 to 4 = Display channels)
Read measuring value block 1 -->
1 2 3 4
- If something different is displayed, refer to Scan Tool operating instructions.
- Only continue with test if coolant temperature is over 85°C (185°F) in channel 1.
- Allow engine to idle for an additional 2 minutes.
- Read Heated Oxygen Sensor (HO2S) voltage in display channel 3.
^ Display will appear as shown:
Read measuring value block 1 -->
1 2 3 4
^ Specification: 0.0 - 0.8 Volts (fluctuating)
Vehicles with 2-pin fuel rail harness connector
- With throttle closed, disconnect (2-pin) Engine Coolant Temperature (ECT) sensor (arrow).
NOTE: The Heated Oxygen sensor voltage in display channel 3 must rise and then drop back to the original figures.
- Re-connect Heated Oxygen sensor harness connector.
NOTE: Voltage in display channel 3 must drop and then return again to the original value.
Vehicles with 6-pin fuel rail harness connector
- Pull vacuum hose off fuel pressure regulator and immediately plug off.
NOTE: Displayed value must rise and then return to the original display value.
All Vehicles
- Press --> button.
- Press 0 and 6 buttons to select function 06 "End data output".
- Press Q button to enter input.
- If specified values are NOT obtained:
- Check Heated Oxygen sensor heater Voltage supply and Heated Oxygen sensor heater for continuity.
- Perform electrical testing Refer to Diagnostic Charts / VAG 1598 Pin Out Box / Electrical Checks / Test Step 18. Testing and Inspection
- Replace Heated Oxygen Sensor (G39).
- Check and erase Diagnostic Trouble Code (DTC) memory, if necessary, eliminate any malfunctions.