Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSAUDI2004A4 SEDAN (8E2) L4-1.8L TURBO (AMB)REPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONCOMPONENT TESTS AND GENERAL DIAGNOSTICSOXYGEN SENSOR AFTER CATALYSTSENSOR AND SENSOR CONTROL CHECK
2004 Audi A4 Sedan (8E2) L4-1.8L Turbo (AMB)
Sensor and Sensor Control Check
2004 Audi A4 Sedan (8E2) L4-1.8L Turbo (AMB)SECTION Sensor and Sensor Control Check
Oxygen Sensor Control After Three Way Catalytic Converter (TWC), Checking
Display on VAS 5051:
1 - Enter display group.
- Enter "037" for "display group number 037" in field -2- and confirm entry by pressing -Q- button.
Display on VAS 5051:
- Activate basic setting by pressing -A- button.
- Check Oxygen Sensor (O2S) voltage in display field -2-.
- Check Oxygen Sensor (O2S) correction value in display field-3- and diagnosis result in display field -4-.
Display Group 037:
Evaluating display group 037
Display Field 2:
Continuation
If specification in display field 3 or 4 is not obtained:
- Perform test drive to free Oxygen Sensor (O2S) from any possible residues and repeat test.
If specified value in display field 3 or 4 is not obtained, even after a test drive has been performed:
- Replace Oxygen Sensor (O2S) before Three Way Catalytic Converter (TWC).
NOTE: If the Oxygen Sensor (O2S) voltage is OK and after a road test the Oxygen Sensor correction value is still outside the specification, this indicates aging of the Oxygen Sensor before the Three Way Catalytic Converter (TWC).
Checking basic voltage
- Disconnect 4-pin connector -2- (brown) to Oxygen Sensor (O2S) before Three Way Catalytic Converter (TWC).
NOTE: To gain access to the connector, remove coolant expansion tank bolt -arrow- and move expansion tank to side. Fuel hoses remain connected.
- Connect multimeter between terminals 3 and 4 to measure voltage.
- Switch ignition on.
- Specified value: 0.400...0.500 V
- Switch ignition off.
If the specified value is obtained:
- Replace Oxygen Sensor (O2S) after Three Way Catalytic Converter (TWC) -G130-.
If the specified value is not obtained:
- Disconnect 4-pin connector -2- (brown) to Oxygen Sensor (O2S) before Three Way Catalytic Converter (TWC) -G39-.
NOTE: To gain access to the connector, remove coolant expansion tank bolt -arrow- and move expansion tank to side. Fuel hoses remain connected.
- Connect test box V.A.G 1598/31 to wiring harness for Engine Control Module (ECM); do not connect Engine Control Module (ECM).
- Test for open circuit in following wiring connections.
Connector terminal Test box VAG 1598/31 Socket
3 68
4 69
- Repair open circuit, if necessary.
- Check for shorts between two wires.
If the wiring is OK:
- Replace Engine Control Module (ECM).
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.