P0050 is a common OBD2 trouble code. It’s generic, which means it has the same definition for the Audi A4 as any other vehicle.
The cause of P0050 is almost always a bad heated oxygen sensor or wiring issue.
P0050 Definition: Heater Control – Circuit – Bank 2 Sensor 1
P0050 indicates no signal coming from your Audi A4’s Bank 2 Sensor 1 oxygen sensors heater circuit.
The heated element within the oxygen sensor heats the sensor faster than the exhaust can. The heated element reduces emissions by letting the fuel trim enter closed loop operation more quickly.
The A/F sensor is responsible for measuring the oxygen content of the exhaust. The PCM uses this data to adjust the air-fuel mixture to the optimal 14.7 parts air to 1 part fuel.
Circuit
In the case of P0050, the PCM has detected a fault in the circuit that activates the oxygen sensors heater.
Bank Two
Bank one is the part of your A4’s engine with the second cylinder.
Bank one is usually the cylinder head facing a little more forward than the other (toward the engine accessories).
Sensor 1
Sensor one is easier to identify. Start from bank one and follow the exhaust. It’s the first one. It’ll likely be on the exhaust manifold or collector.
P0050 Symptoms: Audi A4
The heated element in the oxygen sensor enables closed-loop operation faster, decreasing engine emissions. If it’s the only code you retrieved, you probably won’t notice any drivability issues with your A4.
- Slight decrease in mileage
- Check engine light
- More noticable exhaust smell when driving at first (like gas)
P0050 Causes + Diagnosis: Audi A4
Here are the most common causes of P0050 in the Audi A4, presented to you in a somewhat proper order of diagnosis:
1. Check the Wiring on Bank 2 Sensor 1
Since P0050 indicates a fault in the heated O2 sensor circuit, check the wiring harness for damage.
Pay extra close attention to where the harness may have rubbed up against something or been damaged by road debris. Look for burnt, frail, or damaged wiring. Wiring issues are a VERY COMMON cause for P0050.
Take a look at where your A4’s oxygen sensor plugs into the wiring harness and see if there has been any damage to the pins or if the wiring harness is breaking at the pigtail.
If the pins appear corroded, get some electrical contact cleaner and clean them up. If they are damaged, you will need to repin or replace your wiring harness.
2a. Verify the O2 Sensor is Bad- Swap Test
This method does not work if your A4 has P0050 AND P0030.
If your Audi A4 happens to be a V6 or V8 model, you can do the “swap test.” This test involves clearing the codes and seeing if the code “jumps” to bank 2. It’s a great test because it’s foolproof and easy.
Here’s how the swap test is done:
- Clear the DTC codes with your scanner.
- Swap the Bank 2 Sensor 1 O2 sensor with the Bank 2 Sensor 1. It’ll be on or right after the exhaust manifold.
- Run your A4’s engine until the check engine light comes back on.
- If the code changes to P0030 (The Bank 1 version of this code), that’s proof enough you need to replace the oxygen sensor you swapped.
- If the code remains P0050, you’ll need to continue pursuing your diagnosis, knowing that both O2 sensors are working fine.
2b. Check the Fuses and Voltage
Check the heated oxygen sensor fuse to ensure that it has not blown for some reason. Then, verify with the key switched to the on position that there’s no voltage at the oxygen sensor. If there is no voltage, you’ll need to find where the short/open is.
If there is voltage at the heater circuit, you’ll need to test the ground for resistance. If you find infinite resistance, you’ll need to repair the ground circuit.
3. Bad Oxygen Sensor
If the oxygen sensor wiring checked out or failed the swap test, it’s time to replace the heated oxygen sensor. Oxygen sensors go bad all the time.
Conclusion
P0050 is almost always caused by a bad wiring harness or oxygen sensor. Good luck repairing your Audi A4!