What is a Bad Oxygen Sensor?

Eddie Carrara

Auto computer codes or diagnostic trouble codes (DTC's) are stored in your vehicles computer when there is a problem with your car's engine or emission controls.  All cars built in the US from 1981 to 1995 were built with a system call OBD1, (On-board diagnostics one), basically the system monitored manufacturers specific systems in the vehicle, if there was a fault with one of the systems, it would send a signal to the computer, and that would activate the '' CHECK ENGINE'' light. 

Think you might have a bad oxygen sensor?  Virtually every car produced since the early 1980's contains a sensor which measures the amount of oxygen in the exhaust, then sends a signal to the engines computer to adjust the fuel mixture being delivered to the engine. 

The oxygen sensor works by sending information to your vehicle’s engine control unit (ECU) to help your car run efficiently as well as to reduce emissions.

Symptoms of a Bad Oxygen Sensor

When you have a bad oxygen sensor, your vehicle will run less efficiently, it can sometimes have a poor idle, erratic jerking at steady throttle, hard starting problems, cause the check engine light to come on, and will cause high fuel consumption.

Thus, when oxygen sensor failure has been determined (When the check engine light comes on and sets an O2 sensor code) the sensor must then be replaced, a costly repair if you rely on a garage to do the work for you.

However, replacing an oxygen sensor is a job that you can do yourself, (as long as the O2 sensor is not completely rotted into the pipe or catalytic converter)  thereby saving you precious time and money. Let’s take a closer look at just what an oxygen sensor does and the steps you can take to do the work yourself.

What is an Oxygen Sensor?

Functioning like a monitor, your oxygen sensor works like this: the O2 sensor tip is located inside of your exhaust pipe, the oxygen sensor detects the percentage of oxygen in the exhaust .

If the mixture is too rich (too little oxygen) or too lean (too much oxygen) than the oxygen sensor sends a signal to the ECU telling it to adjusts the amount of fuel entering your engine accordingly.

The wrong mix of gasoline and oxygen can increase pollutants that exit your vehicles exhaust, thereby harming the environment, as well as potentially causing your catalytic converter to fail or even damage your engine.

So, a properly working oxygen sensor is a necessity for any vehicle.  Neglecting to replace a bad oxygen sensor will usually result in damage to your catalytic converter,costing you an extra $500 -$1000 in repairs if not more.

Oxygen sensor Failure

There are some clear signs that your oxygen sensor is no longer functioning. They can include:

  • Check engine light on
  • A rotten egg odor emitting from the exhaust. 
  • A reduction in fuel economy. 
  • Your catalytic converter fails unexpectedly.
  • Exhaust emissions reach undesirable levels. 
  • Your engine surges, hesitates, skips and bucks.

Replacing and Diagnosing an Oxygen Sensor

You can diagnose the problem yourself if you have access to the right tools including a digital voltmeter or an OBD2 diagnostic tool.  In today's market, you can have an OBD2 scanner or code reader right on your iPhone or any Smartphone for that matter (Click here to go to Auto Computer Codes for more information). 

If it has failed, than consider ordering your replacement part online through a reliable wholesaler such as Amazon or one of their venders to obtain a high quality OEM or aftermarket part at a reasonable price and with an easy return policy if needed.

Once your part has arrived than all you will need is one or two automotive wrenches or oxygen sensor sockets to accomplish the job, I recommend using the heavy duty low profile O2 socket because it's short and durable, it can easily access almost any oxygen sensor and will not spread apart like the tall chrome O2 sensor socket. Again, reference your car’s manual for exact instructions.

With the abundance of sensors and technical gadgetry on today’s vehicles it can seem fairly intimidating to do the work yourself, especially if you need to transfer the connector from the bad oxygen sensor to the new one. I recommend transferring one wire at a time instead of removing all the wires at once. 

Fortunately, an oxygen sensor is one of the easier parts to replace, so if you do the work yourself you will save time and money as well as gain an important sense of achievement.  Go ahead you Weekend Warrior, you can do it!

Oxygen Sensors and Tools

Tools you will need to replace most O2 sensors

These two O2 sensors on this Honda CRV are pretty rusted.