What Gases Does the OBD Detect in the Exhaust?

Schedule Brake Pad Replacement
Service Area

$125.02 - $465.01

Price range for all vehicles
Average rating from 11,884 customers who received a Brake Pads Replacement.

Your engine runs on combustion – fire – which creates exhaust gases. A wide range of gases are produced during normal operation, and they must be controlled because many of them become pollutants when released into the atmosphere. It’s actually a common misconception that the on-board diagnostic (OBD) system on your car detects gases, but it doesn’t. It detects malfunctions with emissions equipment (the catalytic converter, oxygen sensors, fuel tank purge valve, etc.).

Oxygen sensors

Part of the confusion here surrounds the catalytic converter and the car’s oxygen sensor(s). Your car may have one or two catalytic converters, and one or more oxygen sensors (some have multiple O2 sensors located at different points in the exhaust system.)

The catalytic converter is located around the midway point in the exhaust on most vehicles (this can vary, though). Its job is to heat up and burn away exhaust gases present in all automobiles. However, the OBD system does not measure these gases, with the sole exception of oxygen.

Oxygen sensors (or O2 sensors), are responsible for measuring the amount of unburned oxygen in your car’s exhaust, and then transmitting that information to the car’s computer. Based on the information from the O2 sensors, the computer can adjust the air/fuel mixture to ensure that it doesn’t run lean or rich (too little oxygen or too much oxygen, respectively).

Other components monitored by the OBD system

The OBD system monitors a number of different components tied to the fuel/evap system, emissions system, and other systems, including:

  • EGR valve
  • Thermostat
  • Catalyst heater
  • Positive crankcase ventilation system
  • Some components of the AC system

However, the OBD system does not monitor gases – it monitors voltage and resistance that could indicate a problem with those components (and therefire with the overall emissions of the vehicle itself).


Next Step

Schedule Brake Pad Replacement

The most popular service booked by readers of this article is Brake Pad Replacement. Yourmechanic’s technicians bring the dealership to you by performing this job at your home or office 7 days a week between 7AM-9PM. We currently cover over 10k cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Brake Pad Replacement reviews

Excellent Rating


YourMechanic Brake Pad Replacement Service

Average Rating

4.9/5

Number of Reviews

11,884

Rating Summary
11,350
339
70
35
90
11,350
339
70
35
90

Jose

8 years of experience
33 reviews
Jose
8 years of experience
BMW 325i - Brake Pads Replacement (Front) - Redwood City, California
I had a few mechanics from YM and _all_ of them arrived late (some even 2 hours late) , but not Jose! He arrived right on time! I gave him the keys and let him do his job. I am a curious person so I asked him a few questions about his techniques and he had no problem answering them all with detailed explanations! He did run into a problem on my car because of stripped bolts, but he literally went above and beyond and found a way to remove it. Best mechanic ever.
Lexus CT200h - Brake Pads Replacement (Front) - South San Francisco, California
Jose was on time and did a great job on my brakes. He was friendly and explained the entire process. Would highly recommend.

Augustine

11 years of experience
35 reviews
Augustine
11 years of experience
Chevrolet Equinox - Brake Pads Replacement (Front) - Rio Rancho, New Mexico
Augustine was amazing. He was the perfect example of customer service all around. While he was working, I was recommending him to my neighbors. Next time I need work, I will be requesting Augustine specifically!!!!! Please give him a raise or bonus!!!
Toyota Corolla - Brake Pads Replacement (Front) - Albuquerque, New Mexico
Mr. Sanchez showed up on time and finished replacing my rotors and break pads. He was very informative and treats your car like his own. He was very time efficient and communicated very well. I highly recommend Mr. Sanchez’s services!!!!

John

26 years of experience
552 reviews
John
26 years of experience
GMC Yukon XL 1500 - Brake Pads Replacement (Rear) - League City, Texas
I am so happy John is back. I trust him very much. He is efficient and has a tremendous amount of mechanical knowledge. He is a true asset to Your Mechanic.
Ford F-150 - Brake Pads Replacement (Front, Rear) - Alvin, Texas
I like John because he is very knowledgeable about all my vehicles. In addition he is very organized regarding how he performs his work.

Wesley

8 years of experience
45 reviews
Wesley
8 years of experience
Dodge Nitro - Brake Pads Replacement (Front) - Peoria, Arizona
Great experience. Very professional, friendly, and knowledgeable. Highly recommended and will continue to use for future work.

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE