What Are The Downstream O2 Sensor Symptoms?

In modern fuel-injected systems that are present in cars these days, they rely on a variety of sensors in order to provide an optimum air to fuel ratio to the engine at all times. The O2 sensor is one of the major components of the fuel injection system, which tells the ECU the amount of fuel that is being injected in proportion to air in the combustion chamber. Downstream O2 sensor symptoms are related to the fuel system. If an O2 sensor fails then it can lead to a variety of problems and symptoms.

In this article, we will try to discuss various symptoms and how to deal with the problem of the O2 sensor.


What are bad Downstream O2 Sensor Symptoms?

The symptoms can be many due to a failing O2 sensor in the car. They have been categorized as follows-

1. A Glowing Check Engine Light

Since the O2 sensor is a major component of the fuel injection system, are failing downstream O2 sensor will immediately make the car ECU unhappy and the ECU will start flashing the check engine light immediately. Depending on the severity of the failure, there can be a continuously lit check engine light or a flashing check engine light. 

2. Poor Gas Mileage


The downstream O2 sensor is directly responsible for the proper air to fuel ratio of the engine, a failing downstream O2 sensor can lead to a very poor gas mileage because the cars ECU will not be able to calculate a proper fuel burn and as a result, it will either deliver a lean or rich fuel mixture.

3. An Engine That Sounds Rough

Downstream O2 Centre cancer symptom includes rough idling or rough running engines. As we know that O2 sensor plays a very important role in delivering a proper air-fuel ratio to the engine, if the O2 sensor is not working as desired then it can lead to poor fuel mixture, and the engine will run rough and deliver poor performance.

4. Emissions Test Failure

Downstream O2 sensor symptoms also include a failing car emission test. The O2 sensor plays an important part in the car’s emission control system and if the O2 sensor is not working in an optimum condition then it can lead to poor emission test results.

How To Fix Bad O2 Sensor Problems?

Fixing the downstream O2 sensors symptom is not that difficult as it is not a complex component of the car. The modern diagnostic tools easily pinpoint the problem and can tell the exact solution for the car fuel injection system. So fixing the downstream O2 sensor symptom is not that difficult. They can be fixed in the following ways-

1. Replacing Downstream O2 Sensor


If the downstream O2 sensor has itself failed then the easy solution for the problem is to replace the downstream O2 sensor itself. There are many categories of O2 sensor which can be cleaned with a strong acid but it is not generally recommended as it is a very dangerous process and it does not guarantee the OEM spec performance. The O2 sensors are fairly cheap so it is better advised to change them instead of trying to repair them or clean them because it will not fully solve the problem and it is expected that the problem might return back after few months.

2. Engine Tune-Up


A badly maintained engine can lead to the failure of the O2 sensor. It will lead to improper fuel burn, which will directly damage the downstream O2 sensor. So in order to avoid such a situation, it is recommended that the owner should follow the prescribed maintenance schedule of the car. Engine tune-ups are very easy to do and if you are mechanically inclined, then you can do that in your driveway very easily. Even otherwise, it doesn’t cost much to do the same job from a mechanic shop. A badly tuned engine can also destroy other emission-related components such as the catalytic converter and these can be very expensive to replace as it contains rare Earth metals.

3. Cleaning EGR System

A faulty EGR system or a clogged EGR system can lead to improper fuel burn in the combustion chamber and as a result, it can send fumes that can block the downstream O2 sensor. So in order to improve the O2 sensor performance, it is important that the EGR valve and other emission control-related devices should be checked and cleaned according to the manufacturer’s maintenance schedule.

There are many cleaning products that are nowadays available at the parts store and they can be easily used by the car owner. They don’t require much effort and can be easily done. But certain high cars have very complex plumbing and it requires a very labor-intensive job to get the EGR valve cleaned.

4. Wiring Repair

Sometimes the downstream O2 sensor symptoms can be caused due to faulty wiring. The wiring can fail due to excess heat in the engine bay for it can be damaged due to a rodent attack. The car’s ECU is quick to pick up such a problem and it will promptly indicate you through the check engine light. You will also notice poor engine performance and bad gas mileage.

In order to fix that, properly skilled car electricians can easily handle such jobs. But sometimes in the case of a high-end car, the whole wiring loom needs to be changed as it cannot be repaired. Also repairing of the wiring loom can be done at home if you are electrically inclined and have handled such jobs in past.

The wiring problem should be attended to as soon as possible because it can lead to the failure of other electrical components and can be a fire hazard.

How Much Will It Cost To Fix O2 Sensor Problem?

The O2 sensor problems can be fixed very cheaply. New O2 sensors can cost between the range of 50 to 200 dollars. But in the case of high and cars there they use multiple O2 sensors than the cost can go as high as $1,000. Another repair regarding the O2 sensor can cost in the region of 200$ to 500$.


The downstream O2 sensor symptoms can be easily traced and attend to.  they don’t require much expertise because most of the problem can be identified through obd2 and they promptly show but repairs to be done to the car. If you still have any questions then you can freely comment down below. 


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