Oxygen Sensor: Testing and Inspection
Oxygen Sensor before Catalytic Converter, Checking
Observe all safety precautions: => [ Safety Precautions ] Safety Precautions
View clean working conditions: => [ Clean Working Conditions ] Clean Working Conditions
Prior to repair work, perform a preliminary check to verify the condition. Refer to => [ Preliminary Check ] Preliminary Check.
Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.
For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.
• When servicing terminals in harness connector of Heated Oxygen Sensor (HO2S) (G39), use only gold-plated terminals.
Special tools, testers and auxiliary items required
• Multimeter
• Wiring diagram
Test requirements
• Fuse for Heated Oxygen Sensor (HO2S) (G39) OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• A/C switched off.
• Ground connections between engine/transmission/chassis OK.
• Exhaust system between catalytic converter and cylinder head properly sealed.
Function test
- Connect the scan tool.
- Start engine and let it run at idle.
- Select Diagnostic mode 6.
- Select "Test-ID 01: Heated Oxygen Sensor". Refer to test => [ Monitor-ID $01: Oxygen Sensor
Monitor Sensor 1 ] Scan Tool Testing and Procedures.
- Switch ignition off.
If the Monitor Failed:
Checking heater resistance
- Disconnect the Heated Oxygen Sensor (HO2S) (-G39-) electrical harness connector.
- Using a multimeter, measure the resistance of the heater from terminal 3 to terminal 4 of the Heated Oxygen Sensor (HO2S) (-G39-) connector.
Specified value: 2 - 5 ohms with the exhaust system at room temperature
If the specified value was Not obtained:
- Replace the Heated Oxygen Sensor (HO2S) (-G39-). Refer to the Repair Manual.
If the specified value was obtained:
Checking heater voltage
- Disconnect the Heated Oxygen Sensor (HO2S) (-G39-) electrical harness connector.
- Switch ignition on.
- Using a multimeter, measure the voltage from terminal 4 of the Heated Oxygen Sensor (HO2S) (-G39-) harness connector to ground.
Specification: Near battery voltage
- Switch ignition off.
If specified value is Not obtained:
- Check for an open, short to ground or high resistance between terminal 4 of the Heated Oxygen Sensor (HO2S) (-G39-) and fuse S-17.
- If necessary, repair the wiring connection.
If the specified value was obtained:
Checking HO2S voltage
- Disconnect the Heated Oxygen Sensor (HO2S) (-G39-) electrical harness connector.
- Switch ignition on.
- Using a multimeter, measure the voltage from terminal 3 of the Heated Oxygen Sensor (HO2S) (-G39-) harness connector to ground.
Specification: Near 4.76 V
- Using a multimeter, measure the voltage from terminal 1 of the Heated Oxygen Sensor (HO2S) (-G39-) harness connector to ground.
Specification: Near 2.85 V
- Using a multimeter, measure the voltage from terminal 5 of the Heated Oxygen Sensor (HO2S) (-G39-) harness connector to ground.
Specification: Near 2.85 V
- Using a multimeter, measure the voltage from terminal 6 of the Heated Oxygen Sensor (HO2S) (-G39-) harness connector to ground.
Specification: Near 2.50 V
- Using a multimeter, measure the voltage from terminal 2 of the Heated Oxygen Sensor (HO2S) (-G39-) harness connector to ground.
Specification: Near 2.93 V
- Switch ignition off.
If any of the specified values were Not obtained:
Checking wiring
- Remove the Motronic Engine Control Module (ECM) (J623). Refer to the service manual for removal and installation procedures.
- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (-G39-) electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J623) electrical connector T94 for an open circuit.
Specified resistance 1.5 ohms max.
If the specification is Not obtained:
- Check the wiring for high resistance, an open or short circuit to Battery or ground.
- If necessary, repair the wiring connection.
If no malfunctions are found in wiring and the voltage was Not OK:
- Replace the Motronic Engine Control Module (ECM) (J623). Refer to the Repair Manual.
Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Scan Tool Testing and Procedures.
2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Scan Tool Testing and Procedures.
3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.