Oxygen Sensors, otherwise referred to as O2 Sensors, and their related check engine light codes, can be troublesome at the very best! Today we discuss the design and function of these sensors, and some of the pitfalls encountered during the diagnosis of their related fault codes.
It seems as though the check engine light and O2 Sensor codes have always gone hand in hand. Fact is, when oxygen sensors were first being used, they did tend to fail.
But manufacturers have been redesigning and tweaking these parts for over twenty years, and nowadays they are fairly bullet proof! Oxygen sensor codes no longer mean "replace the oxygen sensor", and this mindset can be costly! So what goes wrong during the diagnosis of these systems? Well, let me share my experience and you can take it for what it's worth! Nearly all engine control systems are comprised of multiple sub-systems. These sub-systems each depend on correct input from other areas of the electronic engine control system in order to perform their individual tasks properly.
Confused yet? Keep reading, it'll make sense soon! There are a large number of codes relating to oxygen sensor faults. There are also a lot of faults that are often incorrectly thought to be caused by a bad oxygen sensor also referred to as an O2 Sensor. The O2 codes relating to circuit faults can be tested fairly easily. For help on these codes, check out our Generic OBDII list and definitely read our article on diagnosing the wiring related portion of a trouble code.
You will also run into codes for the O2 heater circuits. Newer O2 sensors have heaters as part of their design. This allows them to get up to temperature quicker and begin functioning sooner, resulting in lower overall vehicle emissions. If you ever need specific in depth code help, use the "Get Help" link and we can run down the basics with you as needed. The codes that may give you more of a run for your money are the POP generic or similar manufacturer specific codes.
These are known as rich and lean codes, and almost as often as I've seen new oxygen sensors installed for these codes, I've seen the same vehicles need re-diagnosis! First we need to understand how an oxygen sensor works.
The oxygen sensor screws into the exhaust and the sensor end protrudes into the pipe so that exhaust gases pass across the sensors internal element.
Oxygen Sensor Codes: Avoiding The Common Pitfalls
There is a steel shielding with slots that direct exhaust flow across the actual element. As a note, oxygen sensors used to determine engine fuel ratios are always located in front of the catalytic converter. The sensors behind the cats are called monitors and we will discuss these later.As the engine in your car is running, it puts out certain gases as part of the reaction of the combustible engine.
Oxygen is one of those gases, and to keep the engine running at optimal performance, your car needs to measure the amount of oxygen in the exhaust. But the big question in all this is, will a bad O2 sensor cause a misfire in your car? The amount of O2 your car is exhausting will cause your car to adjust the air to fuel ratio to maximize its efficiency. Other parts of the car that get adjusted are the fuel injectors and the engine timing. When the O2 sensor fails, there are several symptoms, including your check engine light, worse gas mileage than normal, and rough engine idling.
But will a bad O2 sensor cause a misfire? The short answer is yes, a bad O2 sensor can cause your engine to misfire. But why is that? As explained, the O2 sensor sends information to the PCM to adjust engine components to run the most efficiently. A lean mixture means the engine is letting in too much air, but not enough fuel for the reaction in the chamber.
You can check our article on the cost of replacing an O2 sensor here. If you suspect that you may have a bad O2 sensor, you should get it diagnosed and repaired immediately to prevent damage to your engine and the environment.
The Car Moguls. What Does an O2 Sensor Do? Length Sensor to Lead mm 17 in. Directly Fit your vehicle when the plug and the length is the same as your original sensor. If you have any questions, please email us, we try to answer all emails within 24 hours. Bosch Oxygen Sensor, Original Equipment BMW Designed to determine the oxygen content of the exhaust gas Improves fuel economy and lowers emission Made from durable material Facilitate easy installation.
If the only code that comes up is an O2 sensor code then you may have a bad oxygen sensor or you might have a fuel mixture problem. The most common cause of a misfire that I have seen on this engine is a bad valve seat. Most of the time this will set a misfire code for that particular cylinder, but not always.
What a mechanic would do to diagnose this would be to install a computer scan tool to see what the O2 sensors are reading. If the voltage of the sensor is not fluctuating then the sensor may be bad. If it is then they would check the fuel trim readings to see if there is a fuel mixture problem. I would enlist the help of a certified mechanic that has a scan tool and knows how to read this datalike one from YourMechanic. Q: O2 sensor causing misfire. I have a misfire.
The computer is giving me a code that says the O2 sensor is at fault. Robert Tomashek Automotive Mechanic. Thank Robert. Was this answer helpful? Thank you for your feedback! Sorry about that. Why wasn't this information helpful? Recommended Services. The statements expressed above are only for informational purposes and should be independently verified.
Please see our terms of service for more details. Related Questions. Diagnostic code p what does it mean and what steps do i take to fix by Veronica T. My Chrysler Pacifica is shaking pretty bad what could this be by Missy. Serpentine belt came off of Toyota Camry by Zoe R. The Check Engine Light came on, I hooked it up to my scanner and got the code P cylinder 8 misfire. Loud rattling from power steering pump by Eric P.
Squealing brakes by Peter I. Home Questions.Q: Hi James. I keep having an oxygen sensor fault code for a lean exhaust with my '97 Corvette. I've taken the vehicle to the dealer several times but the problem keeps recurring. I would like to try and diagnose the problem myself instead of just paying for the dealer to guess. Also, when determined which sensor has the problem, the scan tool refers to Sensor 2 Bank 1 or Sensor 2 Bank 2.
Which sensor are they referring to? Can I just remove the oxygen sensors and plug the holes? A: Brian, don't remove any sensors from your vehicle.
Your vehicle's onboard computer relies on an array of sensors to determine what you would like to happen next. These sensors, or inputs, send information to the vehicle computer microprocessor which processes the information, then the computer will determine what action should be taken and sends a signal to several output devices to change or control functions of the engine, transmission, ride, or any other operations.
Understanding how oxygen sensors work will help you diagnose problems without having to rely completely on a repair shop. Oxygen sensors act as low-voltage producers, such as how a microphone uses piezoelectric generation to produce an electrical voltage signal from mechanical vibration.
An example of this is an oxygen sensor O2which acts like a miniature generator and produces its own voltage when it gets hot. Now, let's discuss some history of oxygen sensors, how they work, and some common problems associated with them. The first oxygen sensor was used on a Volvo in California vehicles started using oxygen sensors inand by federal emission laws made O2 sensors virtually mandatory on all cars and light trucks.
The O2 sensors are always located in the exhaust and monitor how much unburned oxygen is present in the exhaust. The O2 sensor used in most vehicles is a voltage generating sensor.
The tip of the sensor, which is inserted into the exhaust, has a bulb that is coated with zirconium ceramic on the inside and a porous platinum on the outside. Inside the bulb are two strips of platinum that serve as electrodes, or contacts. The inside of the bulb is vented through the sensor housing to the outside atmosphere. The O2 sensors are constantly measuring the oxygen content inside the exhaust flow and comparing it to the air outside of the exhaust. The engine controller then uses the sensor's voltage signal to alter the fuel mixture, creating a feedback loop that is constantly rebalancing the fuel mixture.
Note: if the exterior of the sensor is covered with oil or debris, the sensor cannot breathe and will render a faulty reading. When the bulb of the O2 sensor is exposed to hot exhaust, the difference in oxygen levels across the bulb creates a low voltage somewhere between 0. For this test you will need a scanner to read the oxygen sensor voltage. We will be using an affordable Actron scanner that can be purchased at any local parts store. If the fuel mixture is burning rich, less oxygen will be present in the exhaust and the voltage will be above 0.
If the fuel mixture is burning lean, more oxygen will be present in the exhaust and the voltage will be below 0. This is difficult for the engine controller to achieve. On a normal operating O2 sensor you should see the voltage bounce around quite a bit from rich to lean. A simple test using the scanner to see if the O2 sensor is capable of reading correctly while monitoring the O2 voltage is to make the fuel mixture artificially rich by feeding propane into the intake manifold or tapping the accelerator several times quickly.
You should see the O2 voltage go high, or rich. In the open loop mode the engine operations are controlled by a predetermined specification contained in the computer's memory.
Oxygen sensors containing three or more wires are called heated O2 sensors. They will warm up and reach operating temperature faster, which allows the engine controller to go into closed loop faster to help reduce emissions sooner.In this specific case, my Nissan Titan would almost stall at idle, there was some hesitation when accelerating, and I could feel some vibration from the engine intermittently. What was a surprise was the number of fault codes the ECM engine control module threw.
In total, my OBD reader found five fault codes:. As you can see, the biggest question was where to begin. Typically if you have 1 or 2 faults codes show up, it can be easy to identify your issue, but this was something different.
Each of these fault codes has its own set of troubleshooting steps to identify the issue. As mentioned before, when the check engine light came on, the engine had already been running a little rough. The P said it was a random cylinder misfire and really didn't give much information other than that. I figured that would be a good place to start.
I picked up some spark plugs and, when I got home from work, I dragged out my spot lights and got to work in the driveway.
After an hour or two, my hands were freezing and I had a couple scraped knuckles, but the truck had eight brand new spark plugs and it was time to start it up to see if anything had changed. All hope was lost. After starting the truck, it displayed the same symptoms as before. The next day, I decided I needed to reach out to a few automotive friends and explain my dilemma.
The general consensus given the symptoms prior to the light coming on, was that I was heading in the right direction. The possibility that it would be a bad ECM was a little unsettling, because of the potential cost of replacing it. The suggestions I received seem to be all over the map, so I decided it was time to do some of my own internet research. What I came across was a lot of forum discussions and a lot of people frustrated with the fault code P because of the lack of information it provides.
I did however come across one forum post where the writer described something very similar to my problem, so I read the whole thread.
Understanding Oxygen Sensors to Diagnose Fault Codes
After a lot of back and forth on that particular post and the writer replacing and testing multiple parts, it ended up being an O2 sensor that solved his problem. Now that I had a few potential causes for my issue, it was time to decide what to try first. I first checked the air intake for any leaks or cracks in the intake hose. Everything checked out fine in that department. Next I pulled the MAF sensor, which is mounted in the intake hose.
I had heard that even if the sensor looks clean it could be dirty enough to be sending incorrect messages to the ECM, which in turn can affect the air fuel mixture in your engine.
I cleaned the sensor with mass air flow cleaner and reinstalled it. After starting the truck, there was no change—still running rough.Based on Illinois Environmental Protection Agency data test, the most common trouble codes that cause an OBD II plug-in emissions test failed on many vehicles and make the Check Engine light on would be fouled or a worn out catalytic converter.
More common trouble codes that cause vehicles fail on emissions test and make the Check Engine light coming on can found below.
Q: O2 sensor causing misfire.
Even fouled or the worn out catalytic converter is the most cause failed on test, based on above data you will get a somewhat different picture, if all of the related codes by system or component to be combined.
Make sure there no new trouble codes appears again, you should OBD monitors self-test run completely you can verify it using a scan tool. Speed in the rotating crankshaft will slight loss caused by misfire, and the OBD II system logs will say as a misfire.
The last two digits of misfire codes will tell you the cylinders number that misfiring. Lean fuel mixture, leaky vacuum brake booster, leaky intake manifold gaskets, cracked or loose vacuum hoses, or another vacuum leaks is the cause of misfires code P appear. The P or P misfire code is set usually caused by lean mixture, it can means the engine is getting too much air, or engine is not getting enough fuel, possibly through a leaky EGR valve or a vacuum leak.
Some factors that cause random misfires will set code P such as low fuel pressure or dirty fuel injectors. This type code also can be caused by bad gas that contains too much air or alcohol. Misfire codes such as P, P, etc. Possible causes can vary such as compression-related leaky head gasket or burned or bent valvefuel related dirty or dead fuel injectorignition-related coil-on-plug ignition coil or bad plug wire, fouled or worn spark plug.
If you want to get rid of the cause of misfire, all these possibilities should be investigated. Fuel vapors will not escaping from the fuel tank due to the Evaporative Emission Control. To storing or capturing fuel vapors, the EVAP system includes a charcoal canister and vent hoses, and the siphoning the fumes will be sucked into the engine when it running by the purge valve. Also, it has vacuum sensor or a pressure sensor for detect vapor leaks small and large. EVAP leak detection system or a fault in the purge valve, a leaky EVAP storage canister, loose or cracked fuel tank vapor hose will be indicated by a small leak code P For gas cap problem, make sure it fits tightly, and you can check it yourself.
However to diagnose another problem, it will be difficult and usually you need a professional help. Small leaks easier to find, because to create a vapor-like smoke the machine heats the mineral oil, it may contain dye of UV leak detection.
Cycle the purge solenoid and other EVAP self-test can be run using a professional level scan tool which have a bidirectional communication ability. Low Fuel Pressure Leaky fuel pressure regulator or weak pump can cause low fuel pressure. When engine idle check the fuel pressure using fuel pressure gauge. If the check result tell fuel pressure less than specifications, it could be the fuel pressure regulator may be leaking, you have a bad wiring connection or your fuel pump may be failing, or your fuel filter may be plugged.
Dirty fuel injectors To fix the problem, use fuel system additive to clean the injectors or clean the injector professionally by a technician. Do not touch the sensor wires and do not clean the sensor with anything else. Oxygen amount in the exhaust monitoring by oxygen sensor, so the fuel mixture can be adjusted by the PCM in order to maximize fuel economy and minimize emissions.
O2 sensor performance codes and O2 heater circuit codes are two types of oxygen sensor trouble codes. Circuit that warms up the oxygen sensor when your engine is first started, will be detected as fault by Oxygen Sensor, and it will set a heater codes.
This is needed to decrease cold start emissions. Increasing in tailpipe emissions due the converter does not work because it has become contaminated. Contamination occurs because it is worn out from age, or leaking coolant internally or engine burning oil.
Converter activity is monitored by the downstream oxygen sensor. The efficiency of the converter can be determined by reading upstream and downstream oxygen sensors, and to determine the level of efficiency, then the computer will compare the results. Code P or P will be set if the efficiency drops below a certain point. The converter has reached the end of the road and needs to be replaced if the output code is nine times out of ten. The only way to fix failing converter is to replace it, because the failed converter can not be rejuvenated.
It will be considered an emission tampering, if you remove it altogether, and that is not an option. Your vehicle will fail on the emissions test, because converter is missing.I utilize several major auto parts franchise chains.
Having said that, I must say that I have noticed a frustrating trend concerning the latter:. Several major auto parts stores offer free diagnostic trouble code retrieval. If the recommended component replacement rectifies customer complaint, then all is well in the world. If it does not, the frustrating part begins. A code, alone, does not constitute an accurate diagnosis. When I attempt to politely inform the clever consumer that the purchased component is unlikely to effectively repair his vehicle, what I get is more attitude.Subaru Misfire, O2 sensor Codes Viewer Participates! Pt2
After the component is installed and the service engine soon light returns as expectedan accurate diagnosis is recommended and guess what — more attitude. In the long run, this customer has spent more money than if a proper diagnosis had been performed, initially.
A thorough and accurate diagnosis must be performed prior to condemning a particular component. Granted, there are exceptions to any rule and there are times when a carline or manufacturer will have an issue with EGR valves, but clogged intake passages, faulty delta process flow EGR sensors, EGR control solenoids, and vacuum and exhaust hose leaks occur with a much greater degree of regularity than faulty EGR valves, themselves.
Several times during the last three years, I have had customers show up with brand-new, expensive oxygen sensors from Brand-X Auto Parts. Again, I am forced to explain what only time and experience has taught my crew, and I. A lean exhaust condition, not faulty oxygen sensors, is at the root of the problem. On one particular occasion, I could hear the sound of a loud vacuum leak emitted from under the hood of a Ford Explorereven before the customer informed me that her new oxygen sensors were on the front seat.
Lean exhaust is caused by one of two things: An excess of air to the engine or insufficient fuel. Before you purchase hundreds of dollars worth of oxygen sensors, consider whether or not you have a vacuum leak at the intake; then check your records for a fuel filter change. Chances are that it will fix your problem. This variation is caused by a weak or failing cylinder, but can be contributed to a variety of factors.
Before you perform an expensive maintenance tune-up, in order to correct a misfire code, perform a complete and accurate diagnosis. The money that you save might be your own. I am a freelance author with over 25 years of experience as a professional, ASE certified automotive technician and shop owner, muscle car enthusiast, avid street racer, and classic car restoration specialist.