"Service engine soon" light is

Well if indeed you need a converter is can cause a complete failure to get your exhaust out of your engine and the energy has to go somewhere like maybe blowing a head gasket which can be very expensive. It is a good idea to change out the O2 sensor with the converter. But if you want to feel safer get a 2nd opinion however I think this guy is being honest. You can try one more thing...take the negative battery cable off and reset your computer by putting it back on after a minute. If after 10 minutes it comes back on...it does need servicing.

False, if the sensor is bad then all it will do is cost you more fuel, and if the converter is clogged, then it will make the engine hard to run(drive with power loss). you did not tell me what vehicle is so this is best I can say with what I know about the vehicle. let me know

I would go to an Autozone or Oreillys and get a free scan. Get the code numbers from the Autoparts man and see if it jives with what you were told earlier. There can be an effect on the car later because the Engine Management system makes adjustments automatically to compensate for problems. It can overcompensate in regulating fuelmix.

When you get your Codes from the Autoparts man you can contact us again with the reply feature for help. Ask the man to clear your computer and see if the service light returns. For the way the diagnostics work, the problems go in sequence and that causes some errors in reporting.

Your Catalytic converter may have an O2 sensor before and after it. Like a,b and c. When c goes bad it may blame b for causing it. You replace c and try it because the scanner can be wrong in saying b is bad too. The tests for b, the Catalytic converter, depends on c, the sensor to accurately measure the exhaust chemicals. If the sensor(c) is bad, putting on a new sensor will tell you if the exhaust chemicals are good.

You will continue to get a light for 25-35 Startups if the computer is not cleared. I hope you find my solution helpful. The aftermarket for Cat converters is more reasonable now.

You need the actual codes (the numbers) - that mechanic should know that a bad O2 sensor will affect drivability, gas mileage and possibly lots of other things-and, how did he determine the cat is bad? You don't mention the year or engine in your truck, but if the cat is bad and it has a bank 2 sensor, that sensor can measure the ability of the cat to do it's job (get hot enough to burn unburned fuel)-therefore the O2 sensor is good. Also, a new cat is expensive-I souldn't buy one unless I knew it was defective (like plugged, but then your truck would barely/not run).

Wont damage engine if its just the oxygen sensor, but if engine light is on, you dont get as good fuel milage. so i recommend replacing the sensor first but only do the converter if you dont have any top end power