Oxygen Sensor Heater, Checking

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements 

• The Heated Oxygen Sensor (HO2S) -G39- fuse is OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• Vehicles with automatic transmission, shift selector lever into position "P" or "N".
• A/C switched off.
• Ground connections between engine/transmission/chassis OK.
• Ignition switched OFF.

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK 

Start diagnosis 

-- Remove the engine cover with air filter. Refer to the Repair information.

Checking internal resistance

-- Disconnect the Heated Oxygen Sensor (HO2S) -G39- electrical harness connector.

-- Using a multimeter, check the Oxygen Sensor (O2S) Heater -Z19- terminals 3 and 4 for correct resistance.

Specified value: 2.5 to 16.0 Ω (at approx. 20° C)

If the specified value was Not obtained:

-- Replace the Heated Oxygen Sensor (HO2S) -G39-.

If the specified value was obtained:

Checking voltage supply 

-- Turn the ignition switch ON

-- Using a multimeter, check the Oxygen Sensor (O2S) Heater -Z19- electrical harness connector terminal 4 to engine ground for voltage.

Specified value: Battery voltage.

-- Switch the ignition OFF.

If the specified value was Not obtained:

-- Check the wiring for an open, high resistance or short to Ground and replace any open fuse.

-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If the specified value was obtained:

Checking Ground activation 

-- Remove the Engine Control Module (ECM) -J623-. Refer to the Repair information.

-- Using a multimeter, check the Oxygen Sensor (O2S) Heater -Z19- electrical harness connector terminal 3 to the Engine Control Module (ECM) -J623- electrical harness connector T94 terminal 51 for an open circuit. Refer to Wiring Diagrams for pin locations.

Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminal	Engine Control Module (ECM) -J623- electrical connector T94 terminal or test box socket
3	51

Specified value: 1.5 Ω max.

If the specified value was Not obtained:

-- Check the wiring for an open, high resistance, short circuit to each other, Battery (+) or Ground.

-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and if the voltage supply was OK:

-- Replace the Engine Control Module (ECM) -J623-. Refer to the Repair information.

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 .
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 .