HO2S Before Three Way Catalytic Converter (TWC), Checking

Heated oxygen sensor, checking


NOTE:
- G39 = Heated Oxygen Sensor (HO2S), bank 1
- G108 = Heated Oxygen Sensor (HO2S) 2, bank 2
- Functional check of HO2S -G39- or -G108-.


- Disconnect Heated Oxygen Sensors (HO2S) -G39- or -G108- harness connector (component locations, refer to "Component Overview - II" Locations ).







- Switch multimeter (Fluke 83 or equivalent) to measure resistance (ohms) and check for continuity between terminal 4 oxygen sensor signal wire (measured at oxygen sensor connector) and engine Ground (GND).

If continuity is not obtained:
- Replace heated oxygen sensor.

If continuity obtained:







- Switch multimeter to 2 volt range and connect between terminal 4 on harness connector and engine Ground (GND).
- Switch ignition ON.
Specified value: 400 ± 50 mV

If the specified value is not obtained, check wiring to ECM as follows:
- Switch ignition OFF.
- Connect VAG 1598/19 test box to ECM harness connector.
- Check wiring for continuity between terminal 4 (HO2S -G39-) and terminal 20 on ECM connector A.
Specified value: max. 1 ohms
- Check wiring for continuity between terminal 4 (HO2S 2 -G108-) and terminal 21 on ECM connector A.
Specified value: max. 1 ohms

If the specified value is not obtained:







- Eliminate short or open circuit in wiring using wiring diagram.

If wiring OK:
- Replace ECM.

Oxygen sensor heater, checking







NOTE:
- Z19 = Oxygen Sensor (O2S) heater, bank 1
- Z28 = Oxygen Sensor (O2S) heater, bank 2
- For functional check of O2S heaters -Z19- or -Z28-.


- Disconnect O2S heater connector -Z19- or -Z28- (component locations, refer to "Component Overview - II" Locations ).
- Switch multimeter (Fluke 83 or equivalent) to measure voltage and connect between terminals 1 (B+) and 2 (GND).
- Start engine and let idle.
- Specified value: approx. 12 to 14 volts

If the specified value is not obtained:
- Check oxygen sensor heater fuse.
- Check fuel pump relay Testing and Inspection
- Check wiring for continuity between terminal 1 and fuse in fuse holder using wiring diagram (if necessary check terminal assignments).
- Specified value: max. 1 ohms
- Check wiring for continuity between terminal 2 (O2S heater -Z19-) and terminal 10 on ECM connector E.
Specified value: max. 1 ohms
- Check wiring for continuity between terminal 2 (O2S heater -Z28-) and terminal 9 on ECM connector E.
Specified value: max. 1 ohms

If the specified value is obtained:







- Switch multimeter (Fluke 83 or equivalent) to measure resistance (ohms) and connect between between terminals 1 and 2.
Specified value at room temperature: approx. 2 to 5 ohms


NOTE: With small increases in temperature, resistance will increase sharply.


If the specified value is not obtained:
- Replace heated oxygen sensor.