Oxygen sensors provide extremely valuable information about the O2 in the gas. If there is a problem with the oxygen sensor, the Check Engine Light will come on which is annoying for all drivers.
This results in many drivers looking for ways to bypass the oxygen sensors so the Check Engine Light will go off. But can you bypass an oxygen sensor and how do you bypass an oxygen sensor?
In this article, we will provide you with the step-by-step process on how to bypass oxygen sensors as well as discuss the potential drawbacks of doing so.
What are Oxygen Sensors?
The oxygen sensor also referred to as a lambda sensor has been around since the 60’s, and was originally designed for Bosch. The electronic sensor measures oxygen in gas. The original design used platinum and ceramic-coated zirconia, but the planar sensor eventually became the most common in mass production.
In 1990, NTK developed the modern O2 sensor for several Honda models. The O2 sensor was made of High-Temperature Cofired Ceramic (HTCC), which provided much better efficiency. All modern cars have oxygen sensors.
The sensor is located in the emissions system. The O2 sensor produces oxygen levels compared to data from the engine computer, which can make adjustments. The sensor affects performances and can warn you if the emissions are causing trouble.
If you live in a state that checks for emissions to drive a car, depending on the trouble, have a mechanic check the O2 sensor, or it could fail you.
At a minimum, there is one O2 sensor before the catalytic converter. There could be a second O2 sensor in each exhaust manifold so it is not certain how many another vehicle has. In many of today’s vehicles, there can be four oxygen sensors.
How to Bypass Oxygen Sensors?
Although you can bypass an oxygen sensor with a dummy O2 sensor, bypassing them is not always the best case.
In some scenarios, it could be illegal, and it could hinder the performance of the vehicle in others. However, it is easy to do when you just have to replace the bad sensor with a dummy.
Here are the step-by-step instructions to bypass an oxygen sensor:
#1. Get the Car Ready.
It’s important to let the hot exhaust system cool completely before starting the work. This will likely take a few hours after driving the vehicle.
Detach the negative battery terminal by loosening the nut and sliding the clamp away from the terminal.
#2. Raise the Vehicle.
You want a vehicle that’s high enough to allow for a climate to work on the exhaust system properly. You will jack up the front of the vehicle on the front jack point.
Once you have the vehicle jacked up, take your jack stands and put them under the frame towards the front of the vehicle and lower the vehicle back to the jack stands.
#3. Unplug O2 Sensor.
Find the O2 sensor you want to remove; it is going to be part of the exhaust system and look like a plug. It could be located anywhere on the exhaust system. You may or may not have two sensors in the catalytic converter: one before and one after.
Unplug the sensor’s wiring. To do this, squeeze the tab on the rear of the connector and pull away from the housing. Then using a special oxygen sensor removal tool, you are going to turn it counter-clockwise, and it should come right out.
#4. Put in Dummy O2 Sensor.
Put the new dummy sensor in; it’s also known as an O2 sensor simulator. To put it in, you will turn the sensor clockwise as if you were putting in a new O2 sensor.
Plug in the wiring harness and lower the vehicle. You should be able to start the car and see if the Check Engine Light has gone out. You may need to drive the car a short distance to clear the light. Always remember that installing a dummy O2 sensor can depending on where you live, be illegal!
Can I Bypass Oxygen Sensors?
You can bypass an oxygen sensor with a dummy or replacement. Lots of people will do this to put out the Check Engine Light while emissions are not right, or to give them more options while tuning.
If you want to eliminate the first O2 sensor in front of the catalytic converter you will want to buy an O2 sensor simulator. They can be found online. If you want to eliminate the second O2 sensor behind the catalytic converter to knock out the P0420 or P0421 code, you can usually use an adapter.
But it’s not legal in all parts of the country, so you will want to check your local laws before performing this hack. And you won’t want to mess with the upstream O2 sensor, before catalytic converter, unless you know how to perform engine tuning.
The upstream O2 sensor adjusts the fuel and air mixture, so you could potentially mess with engine performance with an improper tune or without an O2 sensor.
The downstream O2 sensor, the one with the catalytic converter, is there to only monitor emissions. Taking it out, does not change engine performance, just means you won’t know when you are doing it properly.
How to Test an Oxygen Sensor?
If you believe there is a bad oxygen sensor on your vehicle, you can test it with a back probe and digital voltmeter.
To test the O2 sensor, you must first locate the wires going to it and perform a visual inspection of them to ensure no damage. If they appear to be worn, then just replace the sensor.
If everything is ok, we will start the car engine and allow it to run until it reaches at least 200 degrees Fahrenheit. This is important for a good reading at the sensor. We will turn the engine off while we will connect the connectors.
With your voltmeter and back probe, test the oxygen sensor at several different points to determine what is faulty. You can connect back probe to the signal wire and connect the positive lead of the voltmeter to the back probe. You will then connect the negative lead of the voltmeter to a ground on the chassis.
Set the voltmeter to the 1-volt scale. Start the vehicle and note the reading on the voltmeter. It should quickly vary with an accurate reading. If the voltmeter reads only 0.5 volts, the vehicle may not be warmed up enough.
If the values are not changing after the cold start, there is a problem with the sensor.
You could create a vacuum leak to see how the sensor responds to a lean condition, or use propane enrichment to test this which is much more straightforward. If you are not familiar with either of these, probably the best option is to go and ask a mechanic.
How do I turn off the rear o2 sensor?
To turn off the rear O2 sensor, just remove it from the car. However, this will turn on the check light, and in order to get rid of it, you will need to either get an O2 sensor simulator or reprogram the ECM.
Depending on where you live, these might be illegal procedures, so do your research before you proceed.
What happens when you cut off your o2 sensors?
When you cut off your O2 sensors, your car will not be getting oxygen readings and will just run off simulated values.
That means your vehicle will not be able to adjust your air/fuel mixture, and account for any altitude changes of weather conditions – causing your car to run poorly or even damage your engine. You will also have the check engine light lit up.
Do I need to have these oxygen sensors?
Yes. Oxygen sensors are required to keep the fuel/air mixture in the cylinders. Without an oxygen sensor, the ECU will not know when it should adjust the fuel/air mixture, and your car will run either too rich (a lot of unburned fuel specific to the ratio) or too lean (not enough fuel).
In either scenario, your performance will decrease and your emissions will increase (and there will be a possibility of engine damage.)
How do you make an O2 simulator?
There are multiple ways to make an O2 simulator. The most common way is to install resistors instead of O2 sensors. The resistors you need vary based on the car model you drive and the type of sensor installed.
Regardless, this is easier to do with the rear O2 sensor than the front, since the upstream sensor needs values for the air/fuel mixture.
You can either use a dummy oxygen sensor or replace it with a resistor with the correct resistance to bypass an oxygen sensor in a car.
Just be aware, that in some areas where you live, bypassing the o2 sensors could be illegal, and unless you program the engine control module for the removal of the o2 sensor, you will either end up with a check engine light and/or performance issues.
Bypassing the downstream oxygen sensor is the easiest way to eliminate the P0420 code. Bypassing the downstream oxygen sensor does not have a negative effect on engine performance. However, in order for the check engine light to not be illuminated, you have to reprogram the ECU/vehicle, too.
Bypassing the upstream oxygen sensor is significantly more difficult due to the importance of that sensor in operating the engine within an optimal mixture of air and fuel.
At this point, I hope you feel informed enough to know if you wish to bypass the oxygen sensors in your car.