Heated Oxygen Sensor Before Catalytic Converter, Checking

This procedure is used to check both Heated Oxygen Sensors (HO2S) --G39-, -G108--

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test Requirements 

• Fuses -- for engine electronics OK.
• Battery voltage at least 12.5 V.
• All electrical consumers such as, lights and rear window defroster, switched off (radiator fan must NOT run during test).
• Ground (GND) connections between engine/transmission/chassis OK.
• Oxygen sensor heater OK.
• Vehicles with automatic transmission, shift selector lever into position "P" or "N".
• The exhaust system free of leaks.
• The parking brake engaged.
• The A/C switched off.
• The coolant temperature at least 80 °C.
• Ignition switched off.

Test Procedure 

-- Perform a preliminary check to verify the customer's complaint. Refer to PRELIMINARY CHECK .

-- Perform the function test in Diagnostic Mode 06. Refer to DIAGNOSTIC MODE 06 - READ TEST RESULTS FOR SPECIFIC DIAGNOSTIC FUNCTIONS .

If specified values are obtained:

-- End diagnosis and switch the ignition off.

If the specified values are not obtained:

Checking primary voltage

-- Disconnect the 6-pin electrical harness connector -1- from the Heated Oxygen Sensor (HO2S) --G39-- and Oxygen Sensor (O2S) Heater --Z19-- (bank 1, sensor 1).

To test the Heated Oxygen Sensor (HO2S) --G108-- (bank 2, sensor 1), perform the following steps:

-- Remove the screw -arrow- retaining the coolant reservoir.

-- Disconnect the electrical connector from Engine Coolant Level (ECL) Warning Switch -F66- at the bottom of the coolant reservoir and set aside the coolant reservoir with the coolant hoses -1- and -2- connected.

-- Disconnect the 6-pin electrical harness connector -1- from the Heated Oxygen Sensor (HO2S) --G108-- and Oxygen Sensor (O2S) Heater --Z28-- (bank 2, sensor 1).

The test procedures for the Heated Oxygen Sensor (HO2S) --G39-- are the same for the Heated Oxygen Sensor (HO2S) --G108--.

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminals 4 to 6 for voltage.

Specified value: 0.400 to 0.500 V

-- Switch the ignition off.

If the specified value was obtained:

-- Replace the Heated Oxygen Sensor (HO2S) -G39-. Refer to Component Locations Overview .

If the specified value was not obtained:

Checking wiring

-- Remove the Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REPLACING .

-- Using a Multimeter --, check the Heated Oxygen Sensor (HO2S) 2 -G108- electrical harness connector terminals to the Engine Control Module (ECM) -J623- electrical harness connector terminals for resistance.

• Heated Oxygen Sensor (HO2S) --G39-- (Bank 1, Sensor 1).

Heated Oxygen Sensor (HO2S)-G39-Electrical Harness Connector Terminal	Engine Control Module (ECM)J623Electrical Harness Connector Terminal or Test box Socket
1	83
2	61
3	51
4	82
6	84

• Heated Oxygen Sensor (HO2S) --G108-- (Bank 2, Sensor 1).

Heated Oxygen Sensor (HO2S)-G108- Electrical Harness Connector Terminal	Engine Control Module (ECM)J623Electrical Harness Connector Terminal or Test box Socket
1	81
2	59
3	73
4	60
6	59

Specified value: 1.5 Ω max.

If the specification is not obtained:

-- Check the wiring for a short circuit to Battery positive (+) or an open circuit.

-- If necessary, repair the wiring connection.

If no malfunctions are found in wiring:

-- Replace Heated Oxygen Sensor (HO2S) --G139-- or Heated Oxygen Sensor (HO2S) --G108--. Refer to Component Locations Overview .

-- Erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .

-- Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to READINESS CODE .

-- End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

-- Replace the Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REPLACING .

-- Assembly is performed in the reverse of the removal.

After 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 .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .