Oxygen Sensor Before Catalytic Converter, Checking

Special Tools And Workshop Equipment Required 

• Multimeter
• Wiring diagram.

Test Requirements 

• The Heated Oxygen Sensor (HO2S) -G39- fuse OK.
  Fig 1: Fuses On E-Box In Engine Compartment, Left Side

  Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.
• The Oxygen Sensor (O2S) Heater -Z19- before catalytic converter 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 (GND) connections between engine/transmission/chassis OK.
• Exhaust system between catalytic converter and cylinder head properly sealed.
• Coolant Temperature at least 80 °C.

Test Procedure 

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

Start Diagnosis 

-- Connect scan tool.

-- Start the engine and let it run at idle.

-- Select "Diagnostic mode 6: Check test results of components that are not continuously monitored".

-- Select "Monitor-ID $01: Oxygen sensor monitoring before catalytic converter".

-- Select "Test-ID $83: Dynamic test".

-- Check the specified values at idle.

Dynamic test		Specified value
		min.	max.
Normal operation		0.350 V	---
Reduced threshold upon suspicion of malfunction in catalytic converter		0.399 V	---

If the specified value was obtained:

-- Switch the ignition off. Generate the readiness code.

If the specified value was Not obtained:

Checking primary voltage

-- Disconnect the Heated Oxygen Sensor (HO2S) -G39- electrical harness connector -1-.

-- Using a multimeter, connect the negative lead to engine ground. Check the Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminals 1, 2, 5, and 6 for voltage.

Specified Value: 2.40 V - 2.99 V 

-- Switch the ignition off.

If the specified value was obtained:

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

If the specified value was Not obtained:

Checking wiring

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

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

Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical connector T94 terminals or test box sockets
1	78
2	79
5	56
6	57

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 (GND).

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

-- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring and the voltage was Not OK:

-- Replace the Motronic 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 .