I recently got a check engine light @ 38K miles on my 08 FIT & replaced the O2 sensor. At that time, the dealer also performed a "software update" for which I was charged. Recently I noticed that I am getting about 4-5 Miles per gallon better mileage (I was getting 29-30 mpg previously consistently during the lifetime of the car ownership -- which I had put down to city traffic and driving style). Has any one seen this? Is it due to a under performing O2 sensor or the software update or something else?

 

wow.. interesting. I'd like to get 3-5mpg better

 

I am surprised they charged for the update. How much did they charge you? The O2 should of lasted longer too but if it threw a code then it needed to be replaced. O2's should last to 110000 miles but start losing efficiency at 50,000 miles on average. I have a '00 year van with 138000 miles and it still has the original plugs and O2s.

 

Overall, they charged me ~ 500$ which included the diagnostic for the check engine light, O2 sensor replacement and software update. According to him, the part itself was ~ 350$. I didn't question him on why he charged me for the software update. I thought it was something routine he had to do when he changed the O2 sensor (recalibration or something?). I know that it is not routine to have this repair so soon, but the car is out of warranty and has been trouble free till now - so I didn't think too much about it. Even the best made parts / cars have a failure rate -- so I am just putting it down to chance.

 

BTW Welcome to Fit Freak. Not to make you feel bad but they overcharged you but you didn't have the headache of buying the wrong part and changing it yourself, so it might be worth it in the long run. It should be warrantied for a year or 12000 miles. Here is a Honda parts website so you can look up any parts that you might need in the future. Majestic Honda - The Internet's #1 Honda Automotive Parts Store Also use the search feature on this site for researching any questions and feel free to ask if you need more help.

If they did add new software that is a good thing but they might of did a what is called a idle relearn procedure. It basically erases the Random Access Memory which stores corrected maps for fuel and timing based on sensor readings with different weather and fuel changes.

 

Ouch! Did they at least take you out for a dinner and movie first??

A dying or "lazy" O2 sensor could definitely affect your gas mileage, but who knows what the software update did. Your mileage was kind of low to begin with, so it's probably just closer to normal now.

 

Thanks for the responses. As a followup, I have ~ 33 mpg over 600 miles and three fill ups in my usual mix of city / highway driving including several traffic jams. So the mpg increase is for real and not just wishful thinking on my part. As you said, may be this is what I should have been getting from the beginning -- well, better late than never.

As far as the software update goes, as you say they may have charged me for the idle learn procedure.

On the other hand, I read some of the other threads on this site and I found the following TSB talking about a software update related to the O2 sensor replacement -- however, I have a 2008 fit which is not covered by the TSB.

http://www.driveaccord.net/forums/at...8&d=1207174855

Either way, I am happy that this is resolved.

 

I did check the bill of materials -- it does say "Updated PCM" which is closer to the TSB I mentioned in the previous post than the idle learning procedure. Hope this helps others in a similar situation.

 

My check engine light went on at around 64K miles for the lower 02 sensor and then two weeks later for the uppper 02 sensor. I replaced each with OEM's (NTK from the dealer) for 200 dollars or so each. Next time will get Denso 02 sensors from Amazon.com. I took the opportunity to adjust the valves and replace plugs with Denso Long-Life Iridium and then after idle relearn (all I do is start the car after reconnecting the battery and let it go through 4 fan cycles) and I picked up at least 3 mpg. It will do 35-36 overall if I'm light-footed and 40 mpg. at 60 mph on the highway. But it looked like one plug had not been tightened all the way from the factory and it benefitted either from that and/or the valve adjustment.

 

Regarding the O2 sensor:


Yes, a "lazy" (slow-reacting) O2 will result in poor mileage (on ANY car, not just Fits or Hondas).

That said, I thought the US government mandated a long warranty (8 years/100K k miles???) on emissions components. Might be worthwhile to call Honda Customer Service and ask, you may get a refund for some of the money.

 

Here is the EPA warranty. http://www.epa.gov/otaq/consumer/warr95fs.txt

Its the latest I could find.