With Manufacturer's Scan Tool
Oxygen Sensor (O2S) and oxygen sensor control before Three Way Catalytic Converter (TWC), checking
NOTE:
Vehicle must be raised before connector for oxygen sensor is accessible
Only gold plated contacts must be used to repair contacts 3 and 4 in the oxygen sensors harness connectors.
Special tools and equipment
- VAG 1551/1552 Scan Tool (ST) with VAG 1551/3 adapter cable
- VAG 1598/22 test box
- Multimeter (Fluke 83 or equivalent)
- VW1594 adapter set
- Wiring diagram
Test requirements
- Fuse 43 OK
- Battery (B+) voltage at least 11.5 V
- Exhaust system between Three Way Catalytic Converter (TWC) and cylinder head must be free of leaks
- Coolant temperature at least 85°C, See display group 04, display field 3
Functional check
- Connect V.A.G1551 (VAG1552) Scan Tool (ST). [1][2]Reading and Clearing Diagnostic Trouble Codes
- Turn on ignition and press buttons -0- and -1- to insert "Engine Electronics" address word 01. Engine must be running at idle when performing this step.
Indicated on display
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08 and press -Q- button to confirm input.
Indicated on display
Read Measuring Value Block
Input display group number XXX
- Press buttons -0-, -3- and -0- to input display group number 30 and press -Q- button to confirm input.
Indicated on display: (1-2 = display fields)
Read Measuring Value Block 30 ->
1 2
- Check status of the oxygen sensor control before Three Way Catalytic Converter (TWC) (display field 1).
NOTE: The numbers in display field 2 will not be set to 1 until the Three Way Catalytic Converter (TWC) temperature has risen to above 352 °C (See display group 34, display field 2).
Display Group 30:
Explanation of 3 digit number block in display field 1
If the specified value is obtained:
- Change to display group 32 as follows:
- Press -C- button.
- Press buttons -0-, -3- and -2- to input display group number 32 (032) and press -Q- button to confirm input.
Indicated on display: (1-2 = display fields)
Read Measuring Value Block ->
1 2
- Check oxygen sensor control learned value at idling (additive) in display field 1.
- Check oxygen sensor control value at part load (multiplicative) in display field 2.
Display Group 32:
If the specified value is obtained:
- Change to display group 33 as follows:
- V.A.G1551: Press button 3
- VAG1552: Press button (up arrow)
Indicated on display: (1-2 = display fields)
Read Measuring Value Block 33 ->
1 2
- Observe Oxygen Sensor (O2S) control in display field 1.
- Check oxygen sensor voltage in display field 2.
Display Group 33:
Notes on display field 2:
- The voltage signal "rich mixture (low level of residual oxygen)" is approx. 0.7-1.0 V.
- The voltage signal "lean mixture (high level of residual oxygen)" is approx. 0.0-0.3 V.
- When changing from "rich" to "lean" and back again (Lambda = 1.0) the voltage jump will change from 0.7-1-0 V to 0.0-0.3 V or back again.
- Due to steep voltage jumps, the oxygen sensor control cannot keep the ideal mixture composition (lambda = 1.0) constant. The control fluctuates constantly between a "slightly too lean" and "slightly too rich" condition.
Oxygen sensor voltage U Lambda in mV
A: High oxygen sensor voltage
- Rich mixture (excess of fuel or shortage of air)
- Higher CO value
B: Low oxygen sensor voltage
- Lean mixture (shortage of fuel or excess air)
- Lower CO value
If the specified values are obtained:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Turn off ignition.
Continuation
If the oxygen sensor control in display field 1 does not fluctuate as stated:
- Press -> buttons.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Perform test drive in order to remove possible residue on oxygen sensor and repeat check.
Observe the safety precautions when performing a road test. Technician Safety Information
If the specified values in display field 1 are not obtained even after a test drive or the value does not fluctuate by at least 2%:
- Check oxygen sensor (before Three Way Catalytic Converter (TWC)) aging. Aging Check
Evaluating display field 32, display fields 1 and 2: Oxygen sensor learned values before Three Way Catalytic Converter (TWC)
Evaluating display field 33, display field 2: Oxygen sensor voltage oxygen sensor before Three Way Catalytic Converter (TWC)
Possible causes of malfunction if oxygen sensor control frequency is too slow:
- The slots or holes in O2S sensor body are blocked
- The O2S sensor vent hole in area of connecting wire is blocked
- The O2S sensor has been overheated (glazed)
- The O2S sensor has been damaged by leaded fuel
Checking oxygen sensor basic voltage
- Remove protective cover (arrows) and disconnect 4-pin harness connector (black) -1- from Heated Oxygen Sensor (HO2S) -G39- before Three Way Catalytic Converter (TWC).
- Connect multimeter using auxiliary cables from VW1594 to measure voltage at terminals 3 + 4 (harness connector to Engine Control Module (ECM).
- Turn on ignition and measure basic voltage.
Specified value: 0.400-0.500 V
- Turn off ignition.
If the specified value is not obtained:
- Check oxygen sensor wiring.
If the specified value is obtained:
- Replace Heated Oxygen Sensor (HO2S) before Three Way Catalytic Converter (TWC) Refer to item 32, Locations
- Check DTC memory, if necessary, repair any malfunctions and then erase DTC memory.
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes
- Display readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the readiness code again. Monitors, Trips, Drive Cycles and Readiness Codes
Checking oxygen sensor wiring for oxygen sensor 1
- Remove wiper arms and plenum chamber cover.
- Connect VAG1598/22 test box to control module wiring harness.
- Check wiring between test box and 4-pin harness connector (to control module) for open circuit according to wiring diagram.
- Terminal -3- + socket 25
- Terminal -4- + socket 26
Wire resistance: max. 1.5 ohms
- Check wiring at harness connector terminals -3- + -4- for short circuit to terminals -1- + -2- according to wiring diagram.
Specified value: Infinity ohms
- If no malfunction is found in wiring, replace Engine Control Module (ECM).