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.
DTC P0161/16545 - Ho2S Heater Circuit Malfunction (Bank 2, Sensor 2)
1996 Audi A4 Base, StandardSECTION DTC P0161/16545 - Ho2S Heater Circuit Malfunction (Bank 2, Sensor 2)
NOTE:
HO2S heater behind 3-way catalytic converter is not switched on at engine start. Heater is switched on when calculated exhaust gas temperature is less than 586°F (308°).
- Inspect Heated Oxygen Sensor (HO2S) connector for looseness and/or corrosion. HO2S is located on driver side of vehicle behind 3-way catalytic converter. Repair sensor connector as necessary. If sensor connector was not repaired, go to next step. If sensor connector was repaired, erase DTC memory and test drive vehicle.
- Turn ignition off. Disconnect HO2S Brown 4-pin connector located in right rear corner of engine compartment. Start engine and let it idle. Using a DVOM, check voltage between HO2S connector (harness side) terminals No. 1 (B+) and 2 (ground). Voltage should be 12-14 volts. If voltage is not within specification, go to next step. If voltage is within specification, circuit is okay. Erase DTC memory and test drive vehicle.
- Verify HO2S heater fuse is okay. Replace if necessary. Check fuel pump relay. See SYSTEM/COMPONENT TESTS article. Using DVOM, check resistance between fuel pump relay fuse and HO2S connector (harness side). See WIRING DIAGRAMS section. Maximum resistance is one ohm. If resistance is within specification, go to next step. If resistance is not within specification, repair open circuit. Erase DTC memory and test drive vehicle.
- Using DVOM, check resistance between PCM connector "E" terminals No. 2 and 3. Maximum resistance is one ohm. If resistance is within specification, go to next step. If resistance is not within specification, repair open circuit. Erase DTC memory and test drive vehicle.
- Using DVOM, check resistance between HO2S connector (sensor side) terminals No. 1 and 2. Resistance is approximately 2-5 ohms at room temperature. With small increases in temperature, resistance will increase sharply. If resistance is within specification, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING in this article. If resistance is not within specification, replace HO2S.
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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.