Heated Oxygen Sensors And Regulation Before Catalytic Converter, Checking

The following procedure is used to diagnose both Heated Oxygen Sensor (HO2S) -G39- and Heated Oxygen Sensor (HO2S) 2 -G108-

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements

• The Heated Oxygen Sensor (HO2S) -G39- and Oxygen Sensor (O2S) 2 Heater -Z28- fuses OK.
  Fig 1: Identifying Fuses On E-Box In Engine Compartment, Left Side

  Courtesy of AUDI OF AMERICA, LLC
• The Oxygen Sensor (O2S) Heater -Z19- and Oxygen Sensor (O2S) 2 Heater -Z28- before catalytic converter OK. Refer to.
• 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 GENERAL DIAGNOSIS .

Start diagnosis

Function test

-- 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 "Test-ID 01: Oxygen sensor monitoring before catalytic converter".

-- Select "Test-ID 131: Dynamic test".

-- Check the specified values at idle.

Dynamic test		Specified value
		min.	max.
Normal operation		0.35009	-
Reduced threshold upon suspicion of malfunction in catalytic converter		0.39990	-

If specified values are obtained:

-- End diagnosis and switch the ignition off.

If the specified values are not obtained:

Checking primary voltage

-- Disconnect the black Heated Oxygen Sensor (HO2S) -G39- electrical harness connector -1- or the Heated Oxygen Sensor (HO2S) 2 -G108-.

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -- electrical harness connector -1- terminals 1 to 5 for voltage.

Specified value: 0.400 to 0.500 Volts

-- Switch the ignition off.

If the specified value was not obtained:

-- Replace the Heated Oxygen Sensor (HO2S) -G39- or the Heated Oxygen Sensor (HO2S) 2 -G108-.

If the specified value was obtained:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

-- Install the test box. Refer to Repair information.

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

-- Remove the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .

-- Using a Multimeter --, check the Heated Oxygen Sensor (HO2S) -G39- or the Heated Oxygen Sensor (HO2S) 2 -G108- electrical harness connector terminals to the Motronic Engine Control Module (ECM) -J220- electrical harness connector T121 terminals for an open circuit.

Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J220- electrical connector T121 terminals or test box sockets
1	52
2	51
5	71
6	70

Heated Oxygen Sensor (HO2S) 2 -G108- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J220- electrical connector T121 terminals or test box sockets
1	15
2	12
5	14
6	13

Specified value: 1.5 Ω Max.

If the specification was not obtained:

-- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

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

-- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

-- Replace the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .

Final procedures 

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 .

-- End of diagnosis.