The best way to diagnose an issue with your car is by using a scan tool. This is imperative if the check engine light is on. However, the troubleshooting doesn’t stop there—the scan tool will display a code composed of letters and numbers, but you’ll have to do some research to figure out what it means before you can resolve it.
If you’re reading this article, you’ve probably seen that your vehicle is displaying code P0161 on your scanner.
Here’s a guide to the important things you’ll need to know about the P0161 code, including its definition, causes, symptoms, and more.
What Does the P0161 Code Mean?
Diagnostic trouble code (DTC) P0161 stands for “O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 2).” It warns about an issue with the Bank 2, Sensor 2 oxygen (O2) sensor’s heater circuit.
Code P0161 is part of a family of codes, listed as follows:
- P0141 – Sensor Heater Circuit Bank 1 Sensor 2
- P0161 – Sensor Heater Circuit Bank 2 Sensor 2
- P0135 – O2 Sensor Heater Circuit Bank 1 Sensor 1
- P0155 – O2 Heater Circuit Bank 2, Sensor 1
Modern oxygen sensors come with heating elements so that they heat up to the ideal operating temperature quickly. They provide feedback to the car’s computer or the powertrain control module (PCM). The heating circuit helps reduce the period in which the sensors are not able to send data to the PCM.
The PCM uses the data from the heated oxygen sensors to calculate the right ratio of fuel delivery and monitor the catalytic converter’s performance.
The Sensor 2 portion of the code’s definition refers to the downstream sensor, which is technically known as Sensor 2. It is located behind the catalytic converter and its primary purpose is to check the amount of oxygen in the exhaust gas after leaving the catalytic converter. Note that if the upstream O2 sensor is deemed untrustworthy by the ECM/PCM, many platforms will begin to use the downstream sensor as a feedback signal for fuel control.
The PCM constantly monitors the signals coming from the heated oxygen sensors. If there’s a questionable change or fluctuation in the inputs, the PCM will issue their respective codes.
The P0161 code only applies to cars with V6 or V8 engines. If your vehicle only has four cylinders, it will only have one bank and, typically, one downstream sensor, so it can’t trigger this code. Instead, a faulty downstream heated oxygen sensor will be set as P0141 or Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 2).
You can read our brief discussion about bank 1 and bank 2 if you need help locating the oxygen sensor that’s possibly faulty. If you’re planning a DIY fix for P0161, it’s also a good idea to brush up on why oxygen sensors need to be heated.
P0161 on Some Chevrolet Vehicles
Code P0161 may appear on some Chevy vehicles. The diagnostic trouble code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300–600 mV. This DTC is set when the vehicle control module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period.
On a 1999 Chevrolet Silverado 1500 4.3L V6, for example, this DTC can be caused by the following conditions:
- An open or a short to voltage on either the HO2S signal or HO2S low circuits
- A malfunctioning HO2S
- A problem in the HO2S heater or its circuit
- A faulty HO2S ground
What are the Possible Causes of the P0161 Code?
What causes the P0161 code? There are a couple of reasons why the PCM could set the code P0161:
- Faulty oxygen sensor
- An issue with the oxygen sensor heater circuit (i.e., an open, a short, or high resistance)
- An issue with the PCM
What are the Common Symptoms of the P0161 Code?
It is possible that you won’t experience any noticeable symptoms along with a code P0161. The only symptom that may alert you to the issue is an illuminated check engine light.
How to Diagnose the P0161 Code
If you have an old O2 sensor that fits your vehicle, you can cut the wires off the sensor and connect a tail light bulb to the heater wires. Those will be two of the four wires that are the same color. They’ll be a different color from the other two wires, which are signal and signal ground for the sensor.
If you have an old O2 sensor that fits your vehicle, you can cut the wires off the sensor and connect a tail light bulb to the heater wires.
– Richard McCuistian, ASE Certified Master Automobile Technician
Once you’ve created that tool, you can connect it to the wire harness so that if the heater is receiving voltage from the ECM/PCM, the bulb will light. Typically, the heater will begin to receive voltage as soon as the key is turned to the ON position, even before the engine is started.
If you don’t see the light illuminate, you’ll need to check fuses and circuits visually to see what you can see. But don’t replace the ECM/PCM for this; usually it’s wiring or connectors. But if the light does illuminate, remove the O2 sensor and check the resistance of the heater. It should be around 6 ohms or so. The heaters do fail to open sometimes and that’s the most common cause of code P0161.
How to Fix the P0161 Code
There’s no single way of fixing the code P0161. Different carmakers have their own specific repair instructions for the DTC, so what works for one model may not work for a different one.
Once you’ve figured out the underlying cause, the next step is to figure out what specific repair will work for the issue. Do some research online to find out some possible fixes for your code, keeping in mind to stick to anecdotes from other DIY-ers with the same vehicle as yours.
For example, certain Chevrolet owners have reported success with replacing the offending O2 sensor—but that’s not to say that this would automatically work for a Ford F-150 that is experiencing the same code.
Another reminder—use a repair manual whenever you’re working on something in your car. When in doubt, it’s better to seek help from a professional mechanic.
If you wish to personally work on your car, you may opt to invest in an ALLDATA single-vehicle subscription. This is helpful not only for this specific repair, but also for other issues you may encounter in the future.
Products Mentioned in this Guide
Oxygen Sensor
Engine Control Module
Technical Reviewer at CarParts.com
Automotive and Tech Writers
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
i have a problem, O2 Sensor bank 2 sensor 2 the people before i owned Mitsubishi montero limited 2003 they wielded the pipe backwards and now the o2 sensor only one size fits it and i cant use any kind of sensor because it wont fit please help
Hello Tovie,
If you have determined the O2 sensor is indeed faulty, you will need to install the correct replacement for your vehicle. In your case, it sounds like you may need to replace a section of the exhaust pipe to be able to install a new sensor.