Oxygen Sensor Heater Before Catalytic Converter, Checking

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements 

• The Heated Oxygen Sensor (HO2S) -G39- fuse 24 in Fuse Panel B 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 -1-.

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -G39- terminals 3 and 4 for correct resistance.

Specified value: 2.5 to 10.0 Ω (at approx. 20 °C)

If the specified value was Not obtained:

-- Replace the Heated Oxygen Sensor (HO2S) -G39-. Refer to the Repair Information.

If the specified value was obtained:

Checking voltage supply 

-- Turn the ignition switch ON

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

Specified value: Battery voltage.

-- Turn the ignition switch OFF

If the specified value was Not obtained:

-- Check the wiring for an open, high resistance or short to Ground.

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

-- If necessary, repair the faulty wiring connection and replace fuse 24 in Fuse Panel B if blown.

If the specified value was obtained:

Checking Ground activation 

If the manufacturers test box is being used, perform the following step.

-- Install the test box.

If the manufacturers test box is not being used, perform the following step.

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

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminal to the Engine Control Module (ECM) -J623- electrical harness connector T94 terminal for an open circuit.

Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminal	Engine Control Module (ECM) -J623- electrical connector T94 terminal or test box socket
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Specified value: 1.5 Ω max.

If the specified value was Not obtained:

-- Check the wiring for an open, short circuit to each other, Battery positive 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.

-- Install the engine cover with air filter. 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 .