P0161 – O2 Sensor Heater Circuit

When you plug an OBD scanner to your car, it may throw the P0161 code. This code can come alone or with others. Either way, the best practice is to troubleshoot and repair it.

First, you’ll need to understand what the code means. That should give you some insight into the vehicle part(s) to focus on if you want to erase the code. Here you’ll find all that and more about the P0161 OBD code.

Code P0161 will usually come with the description “O2 sensor heater malfunction (bank 2 sensor 2) – downstream”
The P0161 trouble code identifies that there is a sensor malfunction in bank 2 sensor 2

P0161 Code Definition

P0161 (Generic):

Code P0161 will usually come with the description “O2 sensor heater malfunction (bank 2 sensor 2) – downstream”. That simply means that a problem has been detected in the heater control circuit. More specifically, the issue is with bank 2 sensor 2 of the control circuit.

What Does P0161 Mean?

Even with the simplified description, this trouble code may still be a bit hard to understand. So how about we break it down some more.

Contrary to old cars, today’s vehicles have both downstream and upstream oxygen sensors. These sensors contain heating elements whose role is to get them (sensors) to operating temperature as quickly as possible. That reduces the amount of time required to provide feedback to the powertrain control module (PCM).

Once they are operational, the downstream and upstream oxygen sensors will now be able to communicate with the PCM. The PCM uses data from these two sensors to control fuel and reduce emissions.

Understanding P0161 And Other Oxygen Sensor Codes

The upstream oxygen sensor – usually shortened to O2S – is located just ahead of the catalytic converter. It determines how much oxygen is in the vehicle’s exhaust gas.

How so? By comparing the amount of oxygen in the exhaust to that of the surrounding air. The PCM uses that information to control air/fuel mixture by regulating injector pulse.

Now, if the upstream oxygen sensor (O2S) is faulty, you will get the P0135 code. So, don’t worry about that sensor if you’re only getting the P0161. Instead, move to the downstream oxygen sensor.

This one is located behind the catalytic converter. It checks whether the converter is operating efficiently. That process involves examining the amount of oxygen in exhaust gas after it has left the converter. It is because of that function that a downstream oxygen sensor is also called a catalyst monitor.

Anyway, the P0161 code indicates that there’s a problem with that particular sensor. To be precise, the PCM has detected a malfunction in the heated oxygen sensor (HO2S) of bank 2 sensor 2.

Bank 2 is the part of the engine that’s on the opposite side of the first cylinder. If the problem was in the first cylinder then you would get the P0141 code (O2 sensor heater malfunction (bank 1 sensor 2). You may also want to know that you can’t get a P0161 code if your car is a single cylinder because it would only have one bank.

What Are The Symptoms Of P0161 Code?

What is the first indication that you will get the code P0161 when you scan your vehicle? The most observable symptom is the Check Engine Light (CEL).

The oxygen sensor heater circuit is powered by a relay that closes right after you crank the car’s engine. The PCM monitors the sensor as well as its circuit and relay. If it detects a problem, it will trigger the CEL (also known as malfunction indicator lamp or MIL for short).

In addition to that, your vehicle may record higher emissions. That’s down to the fact that the sensor is taking too long to heat up and achieve its operating temperature. As a result, the PCM is finding it hard to mix air and fuel as per the required ratios.

Note that the increase in emissions can (and will) also trigger the CEL. Alongside those two symptoms, you may also notice a decrease in fuel economy. That’s usually accompanied by the car engine running rough.

What Are The Causes Of P0161?

Generally speaking, the P0161 code comes about when the amount of resistance in the heater circuit is incorrect. There are set minimums and maximums for resistance. When the value goes beyond these set figures, the PCM detects the abnormality and triggers code P0161.

What causes the resistance to deviate from the set specifications? There are a number of things that can cause this. Here are the main ones:An open circuit in the O2 sensor heater

  • An open circuit in the O2 sensor heater
  • High resistance in the O2 sensor heater
  • Faulty wiring and/or connection to the circuit
  • Short or open ground wire in the circuit
  • Faulty downstream oxygen sensor

How Serious Is P0161 Code?

The P0161 diagnostic trouble code is a moderate to low one; you shouldn’t lose any sleep over it. The vehicle won’t have any drivability issues because of the code. However, you will fail an emission test when subjected to one.

In other words, you don’t have to attend to the code immediately. But you should do so at the first chance you get.

How To Diagnose And Fix The P0161 Code?

Speaking of attending to the P0161 code, below is a step-by-step guide for troubleshooting and fixing the code. You will need your car’s repair/service manual and a multimeter.

1. Perform A Visual Inspection

Many times you will get this code because of damaged or incorrectly routed wires. These are the ones you want to check first.

Ordinarily, the HO2S will have 4 wires. Two of them go to the heater circuit, one carries power and the last one is ground. Be sure to check in your vehicle’s service manual for a reference diagram.

After identifying the correct wires, check to see if they are loose, damaged or incorrectly routed. It is totally okay to splice these wires, as long as you use a high temp wire and do a great job when splicing.

2. Test The Circuit Wiring

If step 1 doesn’t fix the code, go ahead and test the power and ground wires using a digital multimeter. This step will tell you whether the wires have any other fault that is not physical damage.

Start by testing the power feed. You can do that by touching the multimeter’s black connector to the power wire and the red connector to the ground wire. It should give a reading that’s equal or close to the battery voltage.

If the reading is way off, it means that there’s a problem with the sensor’s power relay. Proceed to test the ground side of the sensor. Touch the multimeter’s red lead to the power wire and the black lead to the ground wire. Again, the reading should be equal or close to the battery voltage.

If the reading is off, it means that the ground side of the sensor is faulty. Needless to say, you can splice whichever wire is faulty. In case you’re not feeling so good about your splicing ability, consider replacing the entire sensor.

3. Test The Circuit Resistance

If you find that the power and ground are good, proceed to check the sensor’s heating element for an open circuit or abnormally high resistance.

With your multimeter in the ohms setting, connect its leads to each of the circuit pins on the sensor. Take the reading and compare it with the specification in the service manual. If there’s a mismatch, it means that the sensor is faulty and should be replaced.

Similarly, if the multimeter reads “OL”, it means that the sensor has an open circuit. Again, it should be replaced.

4. Do A Road Test

After all the above, do a road test to clear code P0161. Drive up to 100 miles (not necessarily in one instance) to give the on-board computer a chance to verify that the issue has been fixed.

If you fixed everything properly, the code and the Check Engine Light should both clear. If they return, then there’s a high possibility that the powertrain control module (PCM) is the culprit.

What Common Mistakes To Avoid While Diagnosing Code P0161?

Some people usually rush to replace the oxygen sensor in bank 2 before performing any diagnostics. That’s one common mistake that you should avoid.

While most of the time the sensor is the problem, other times it is a wiring issue. There are instances when the problem is caused by a completely different part altogether.

For example, it may be a faulty catalytic converter, exhaust leak or damaged PCM. Take a careful look at all the other codes that have come with the P0161 and fix them first. Doing that alone can clear code P0161.

It’s also a mistake to attempt to fix the issue if you’re not up for the task. You may end up doing more harm than good. If you feel that you can’t fix code P0161 the DIY way, please hire the services of a professional mechanic.

Most of them will charge under $100 to perform a full diagnostic scan and anywhere between $75 and $150 per hour to fix the issue. It typically takes one hour or less.

Tips To Avoid P0161 In The Future

There are a few things that you can do to avoid code P0161 entirely. The first is proper maintenance of O2 sensor 2 in bank 2 (and all other sensors). Proper maintenance largely means periodical inspection and cleaning.

During inspection, look for damaged wires and splice them. Once that’s done, proceed to clean the sensors. Gasoline is usually used for that, so you’ll need to be extra careful.

With those simple steps, your O2 sensors should work like a charm. But keep in mind that they need replacing after every 100,000 miles. Don’t ignore that fact, otherwise your sensors might fail on you at the most critical moment.

Read more: P0430 Code: Meaning, Symptoms, Causes, and Fixes