There are no codes that specifically tell that your oxygen sensor or related parts need to be replaced, hence it is important to check all the chain of things that are responsible for your specific error code.
Usually, if your oxygen sensor codes keep coming back, it’s because your O2 sensor wasn’t at fault, it could be anything from bad spark plugs to bad wiring. Hence it is important to check all the chain of things that are responsible for your specific error code.
1. The Error Code Didn’t Reset
If you’ve verified that the error code is the same, you may be getting the oxygen sensor codes back because the computer hasn’t realized that the problem is solved. Usually all you have to do to fix this is to either:
- Drive for a bit for the computer to re-calibrate and recognize that the problem that was causing the error codes has gone away.
- Try unplugging your battery for about 30 minutes, but note that disconnecting the battery will likely ease other data as well. (Newer cars use non violate storage for storing data like emissions error codes, so disconnecting the battery might not help)
- If you are certain, use an OBD2 scanner to reset the codes.
2. Your Oxygen Sensor Wasn’t At Fault
As we said, most of time, if your oxygen sensor code keeps coming back its because the O2 sensor wasn’t at fault in the first place, and your probably replaced the O2 sensor for nothing. To prevent this from happening again, use our chart below to understand what those O2 sensor codes actually mean and what are the possible causes of them.
TIP: Never assume a certain part has to be replaced just because the error code included its name in the description
| Code | Description | Possible Causes |
|---|---|---|
| P0150 P0156 | O2 Sensor Circuit Malfunction | – Broken sensor element. – Sensor disconnected. – Shorted wiring. – Catastrophic failure of sensor due to thermal shock. |
| P0151 P0157 P0163 | O2 Sensor Circuit Low Voltage | – Short in wiring between sensor ground and signal wire. – Silicone or ethylene glycol poisoning of the air reference electrode. |
| P0152 P0158 P0164 | O2 Sensor Circuit High Voltage | – Short in wiring between heater circuit and signal wire. – Sensor immersed in water. – Silicone or ethylene glycol poisoning of the sensing electrode. |
| P0153 P0159 P0165 | O2 Sensor Circuit Slow Response | – Sensor electrode protective coated with carbon. – Silicone poisoning. – Ethylene glycol poisoning. – Failed sensor heater. – Heater circuit fuse. |
| P0154 P0160 P0166 | O2 Sensor Circuit No Activity Detected | – Short in wiring between sensor ground and signal wire. – Silicone or ethylene glycol poisoning of the air reference electrode. |
| P0155 P0161 P0167 | O2 Sensor Heater Circuit Malfunction | – Sensor heater shorted or open. – Replacement sensor installed with incorrect heater current values. – Open or shorted electrical connections. Heater circuit fuse. |
| P0156 P0162 | O2 Sensor Circuit Sensor Malfunction | – Broken sensor element. – Sensor disconnected. – Shorted wiring. – Catastrophic failure of sensor due to thermal shock. |
Note: If you received a different error code, a quick google search about the code should do the trick.
3. You Replaced The Wrong Oxygen Sensor
On a modern car, there are two O2 sensors. The first is used to adjust the fuel mixture and the second one checks to make sure the first O2 sensor and the catalytic converter are functioning properly. It is possible the second sensor went bad fooling the computer into thinking the first O2 sensor was failing. It could also be a wiring problem. Less likely, but also possible the computer is being fooled by another sensor that is overriding the O2 sensor input.
Related: How To Tell If a Catalytic Converter Is Clogged
How To Test An Oxygen Sensor
If you want to test if your oxygen sensor is actually at fault for you error codes coming back, you can simply test it with a multi-meter or an OBD2 scanner
1. Remove The Oxygen Sensor
Depending on which error code and bank you got, it will be required to remove the oxygen sensor in various locations because there are multiple oxygen sensors. The first is used to adjust the fuel mixture and the second one checks to make sure the first O2 sensor and the catalytic converter are functioning properly. Although some cars can have as high as 4 oxygen sensors. This is because any car made in 1996 and after are required to have a second oxygen sensor that is located below the catalytic converter, to monitor the efficiency, and indicate if it clogged or damaged.
Air Fuel Oxygen Sensor
Scotty Kilmer has a good video showcasing how it’s done. You can check out his car forum here
Text version:
To get the oxygen sensor off you’ll need an oxygen sensor socket which slides on the cheater bar, which will give you plenty of leverage to get the oxygen sensor loose.
- Locate the electrical connection, from under the car
- Unplug the socket.
- Use the cheater bar with a oxygen sensor socket to loosen the oxygen sensor
- Unscrew the oxygen sensor by hand
- Done
Other Location
if you couldn’t find the oxygen sensor, consulting your owner’s manual or doing a google search about your car will show you where your oxygen sensor is located. But don’t worry, even if it was in an unusual spot, it shouldn’t be that much different from what we showed above, in fact, it might be easier and more intuitive!
2. Determine Which Oxygen Sensor You Have
Before we start the testing procedures, your oxygen sensor might have 1,2,3 or 4 wires, with
- 1 Wire: One signal wire, grounded by the exhaust pipe in the chassis, sends the voltage reading to the ECU.
- 2 Wires: One signal wire, and the wire is going to be a sensor ground wire, and is more reliable than grounding it with the chassis of the exhaust pipe
- 3 Wires: One signal wire, grounded by the exhaust pipe in the chassis, and the extra wire being the heater, which helps your oxygen sensor reach operating temperatures much faster, because your oxygen sensor wont produce any voltage unless it reaches 600 degrees.
- 4 Wires: One signal wire. One ground wire, remaining two wires for heating.
Generally, the black wire is the signal wire, the white wire is the heater and the grey wire is the ground.
3. Test The Oxygen Sensor
A 4 wire oxygen sensor will be used as an example. Since we are using an oxygen sensor with a heater, you need to first measure the resistance for the internal heater.
- Turn on your multimeter
- Put the setting on Ohms (Ω) and set it to 200
- Test the o2 sensor response to a lean fuel consumption situation. Disconnect the hose from the positive crankcase ventilation (PVC) valve which is located on the valve cover. This will allow more air into the engine so the voltmeter should read close to 200mV (0.20V). If the voltmeter does not respond, the o2 sensor is not functioning properly.
- Reconnect the PVC hose to test the o2 sensor’s response to a rich fuel consumption situation. To do this disconnect the plastic hose connection to the air cleaner assembly. Block the hose connection opening with a rag in order to reduce the amount of air going into the engine.
- Check the voltmeter. It should read close to 800mV (0.08V) due to the reduction of oxygen entering the engine. If the o2 sensor does not respond this way, it is not functioning properly.
- Reconnect the hose to the air cleaner.
- If the o2 sensor responded correctly to the lean and rich fuel tests, another component could be causing the problem. The potential issues could be a vacuum leak, ignition system or something similar. Obviously, if the o2 sensor did not respond properly then it is bad and will need to be replaced.
Conclusion
So, after all your testing you should know whether the o2 sensor is bad or if something else is the problem.
If you feel confident that the o2 sensor is bad, you can tackle it yourself. If you’re not sure that the o2 sensor is bad, you should probably take your car to a professional. Remember, addressing the problem sooner than later may save you from more serious issues such as replacement of the catalytic converter