Heated Oxygen Sensor (HO2S) -G39- and Oxygen Sensor Regulation Before Catalytic Converter, Checking
Heated Oxygen Sensor (HO2S) -G39- And Oxygen Sensor Regulation Before Catalytic Converter, Checking
Recommended special tools and equipment
- VAG1526A hand multimeter
- VAG1594A connector test kit
- VAG1598/31 test box
Test requirements:
- Fuses for engine electronics OK
- Ground (GND) connections at engine and transmission OK
- Oxygen sensor heater OK; check.
- Exhaust system free of leaks.
- Parking brake engaged. Vehicles with automatic transmission: Selector lever in position "P" or "N".
- Electrical consumers switched off (radiator fan must NOT run during test).
- A/C switched off.
- Coolant temperature at least 80°C, see "Mode 1: Check measuring values"; "PID 05: Coolant temperature".
Work procedure
NOTE:
- When selecting the diagnostic mode, the entry is always performed in "Bank 1 sensor 1".
- If either the V.A.G 1551/1552 Scan Tool (ST) or the VAS5051/5052 Vehicle Diagnostic, Testing and Information System is used for checking the output of oxygen sensor signals, the respective oxygen sensor can be selected by pressing buttons 1 and 2:
- Button 1 = Bank 1 sensor 1,
- Button 2 = Bank 1 sensor 2,
- When servicing terminals in harness connector of Heated Oxygen Sensor (HO2S), use only gold-plated terminals.
- Connect diagnostic tester.
- Start engine and let run at idle.
- In diagnostic function "33 - OBD", select "Mode 5: Check output of oxygen sensor signals".
- Select the desired output of oxygen sensor signals according to the following table.
Test-ID Diagnostic text
129: Current value of oxygen sensor signal
- Bank 1, sensor 1
130: Specified value of oxygen sensor signal
- Bank 1, sensor 1
131: Dynamic value
- Bank 1, sensor 1
132: Shift of oxygen sensor regulation before catalytic converter via oxygen sensor regulation behind catalytic converter
- Bank 1, sensor 1
- Check values of output for oxygen sensor signals.
If specified values are not obtained:
- Road test vehicle in order to free oxygen sensor of possible residue and repeat test.
If specified values are not obtained again:
- Check primary voltage.
- Test oxygen sensor heater before catalytic converter.
- Check intake system for leaks (false air). Intake System, Checking For Leaks (False/Unmetered Air)
- Check Oxygen Sensor (O2S) and oxygen sensor control behind Three Way Catalytic Converter (TWC).
- Checking system pressure and residual pressure. Fuel System Pressure and Residual Pressure, Checking
- Check fuel injectors. Fuel Injectors, Checking
- Check Evaporative Emission (EVAP) Canister Purge Regulator Valve -N80-. Evaporative Emission (EVAP) Canister Purge Regulator Valve, Checking
- Check Fuel Pump (FP).
- Check exhaust system for proper seal.
- Check Secondary Air Injection (AIR) system for proper seal.
- Check vacuum lines for proper seal.
Checking primary voltage
- Disconnect 6-pin harness connector (black) -5- to Heated Oxygen Sensor (HO2S) -G39- before catalytic converter.
NOTE: Coolant reservoir screw (arrow) must be removed and coolant reservoir must be placed to the side in order to access harness connector. The coolant hoses remain connected.
- Connect multimeter between terminal 1 and 5 for voltage measurement.
- Switch ignition on.
Specified value: 0,400 ... 0.500 V
- Switch ignition off.
If specified value is not obtained:
- Test oxygen sensor wires
If specified value is obtained:
- Replace Heated Oxygen Sensor (HO2S) -G39- before catalytic converter
Check oxygen sensor wires for Heated Oxygen Sensor (HO2S) -G39- (bank 1, sensor 1)
- Connect test box to wiring harness of Engine Control Module (ECM); ECM is not connected.
- Check the following wire connections for open circuit according to wiring diagram:
Harness connector Terminal Test box Socket
1 70
2 71
5 51
6 52
Specified value: Wire resistance max 1.5 Ohm
- Also check wires for short circuit to each other as well as to B+ and Ground (GND).
Specified value: Infinite Ohm (no continuity)
- If necessary, repair wire connection.
If no malfunctions are found in wires:
- Replace Engine Control Module (ECM).
Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check DTC memory, see "Mode 3: Check DTC memory".
2. If necessary, erase DTC memory, see "Mode 4: Reset/erase diagnostic data".
3. Generate readiness code. With Generic Scan Tool
- End diagnosis and switch ignition off.