Sensor and Control Check
Oxygen Sensor (O2S) and Oxygen Sensor Control Before Three Way Catalytic (TWC) Converter, Checking
NOTE:
The oxygen sensor (before Three Way Catalytic (TWC) Converter) has a static regulation and can be differentiated from the oxygen sensor behind catalytic converter via a 6-pin connector.
When servicing terminals in harness connector of Heated Oxygen Sensor (HO2S), use only gold-plated terminals.
Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram
Test requirements
- All fuses must be OK.
- Battery voltage must be at least 11.5 volts.
- Exhaust system must be properly sealed between Three Way Catalytic (TWC) Converter and cylinder head.
- Coolant temperature must be at least 85 °C, See display group 04, display field 3.
Function test
- Connect VAG1551 scan tool (VAG1552). Start engine and select the Engine Control Module (ECM) using address word 01.
Connecting scan tool and selecting ECM. Refer to Scan Tool Connecting and Initial Checks. Scan Tool Testing and Procedures
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.
Indicated on display:
Read measuring value block
Enter display group number XXX
- Press -0-, -3- and -0- for the function "display group number 30", and then press -Q- to exit from input mode.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 30 ->
1 2 3 4
- Check status of oxygen sensor control before Three Way Catalytic (TWC) Converter (display field 1).
Specification: 1 1 1
Explanation of 3-digit value in display field 1:
- Display group 30 and its evaluation
If oxygen sensor heater is not active, that is if it stays at 0:
- Test oxygen sensor heater before Three Way Catalytic (TWC) Converter. Heater Check
If oxygen sensors or oxygen sensor control is not active:
- Change to display group 32 as follows:
- Press -C- button.
- Press -0-, -3- and -2- for the function "display group number 32", and then press -Q- to exit from input mode.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 32 ->
1 2 3 4
- Check oxygen sensor adaptation values (additive) at idle in display field 1. Specification: -5.4 to 5.4 %
- Check oxygen sensor adaptation values (multiplicative) at partial throttle in display field 2. Specification: -10.0 to 10.0 %
- Display Group 32 and its evaluation
If the specified value(s) are not obtained:
- Change to display group 33 as follows: VAG1551: Press button -3- VAG1552: Press up-arrow button.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 33 ->
1 2 3 4
- Display Group 32 and its evaluation
- Observe oxygen sensor control in display field 1. The indication should oscillate in the range from -10.0 to 10.0 % by at least 2%.
- Check oxygen sensor voltage in display field 2. Voltage must oscillate in the range from 1.4 to 1.6 volts.
If one or more of the indications in display field 1 or 2 is constant on one value:
- Switch ignition off.
- Test oxygen sensor wires.
Continuation
If oxygen sensor control in display field 1 does not oscillate in specified range:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Perform a road test to free the Heated Oxygen Sensor (HO2S) of any possible residue, and repeat the test.
Observe the safety precautions that apply to road tests.
If specified value in display field 1 is not obtained even after road test or if value does not fluctuate at least 2 %:
- Check oxygen sensor before Three Way Catalytic (TWC) Converter for aging. Aging Check
Possible malfunctions, when static regulation of oxygen sensor is too slow:
- The slits or holes in sensor head are clogged.
- The ventilation hole at the sensor -near the connector cable- is closed.
- Sensor has suffered thermal overload (glazed).
- The sensor has been damaged by leaded fuel
Check oxygen sensor wires:
- Connect VAG1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.
- Disconnect 6-pin black harness connector -arrow- to Heated Oxygen Sensor (HO2S) -G39- before Three Way Catalytic (TWC) Converter (bank 1).
- Check wires between test box and 6-pin connector (to control module) for open circuit according to wiring diagram.
Terminal 1 + socket 70
Terminal 2 + socket 71
Terminal 4 + socket 05
Terminal 5 + socket 51
Terminal 6 + socket 52
Wire resistance: max: 1.5 Ohms
- Also check all wires for short circuit to each other. Specification: Infinity Ohms
If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) -G39-bank1.
- Read readiness code. If DTC memory was erased or the Engine Control Module (ECM) was disconnected from the continuous B+ supply, the readiness code must be re-generated. Monitors, Trips, Drive Cycles and Readiness Codes Monitors, Trips, Drive Cycles and Readiness Codes