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Discussion Starter #1
Hello! I have an 06 ridgeline RTL I've had for several years. Love the vehicle and have taken care of it. I purchased from a guy who worked for the Honda dealer and they all explicitly told me how well it was maintained there for all its years. It has 230k. Runs great, starts great, drives great. I have done the waterpump/timing belt, tune up (plugs wires pcv etc), new tires, and a few other odds and ends all in the last two years. It sat for about 9 months in storage as I didn't need it for a while....right after all that work. Popped right on and drove great.

I always got about 24 mpg highway - lots of long trips with this car, towing and not towing. ALWAYS over 20mpg unloaded. In the last four months I have watched the fuel mileage plummet to 15 MPG Highway. Went to Chicago and back from mid Michigan last week and I was 15.2 solid highway on cruise control there and back. Something is definitely not right. I just cant figure out what it is. I know winter blended fuel is probably a factor being in norther Michigan - but in years past I never noticed a real difference in MPG.

It is throwing codes P0430 and PO420. well discussed topics on here I know. However it is running seemingly fine everywhere else but fuel consumption. There is not excessive heat coming from the cats or exhaust - temps are normal. There is no loss of flow whatsoever. Doesn't seem to be clogged and both could be working fine? Shop did an oil change and said bone dry not leaking fuel anywhere, filters are clean, etc. When I bought the truck it had a code I do not know anymore that I was told was upstream oxygen sensor at autozone. I did not change that yet BUT it is not throwing a code for that anymore. Just the 430/420.

This is now my wife's car actually for work. She drives upwards of 200 miles per day and is EATING through gas worse than my Escalade EXT or Duramax ever has! Need some help and suggestions on where to start trying to get the mileage back where it should be!! oxygen sensors? injectors? I trust my shop guys saying they don't condemn the Cats yet and in Michigan we have no emissions tests - could care less about the light being on - JUST WANT MY MILEAGE BACK!

Thanks in advance!
 

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2006 Ridgeline RTS in Steel Blue
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Here's a few things I could find quickly. I'll add more but "Highly" recommend searching P420 & P430 using the vB search in the upper right side of the site.
 

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Thanks for that information. I did do quite a bit of research on those codes before posting. I couldn't seem to find anything exactly like my issue. The cats seem to be preforming as expected, just throwing codes. I have cleared them and they come back about about 3-5 starts. I feel like I should start with all the up/down sensors but still feeling unsure.
 

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2014 Sport
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Check your air box for mice. Make sure your exhaust is solid and not leaking. At 230k you should replace all your up / down sensors. Start there and then consider the Cats. Have you ever had your valves adjusted? Do you have a fender liner / under engine plastic panel falling down and catching the breeze? Did you just put on a roofrack? You could get an OBD reader and take a look at the fuel trims using an App like Torque.

How certain are you of your "before" MPG? 20mpg average with 24 on the highway is astronomically good for the first gen Ridgeline's particularly those prior to the 09 update. Are you running non ethanolated gas to get those numbers? Typical winter gas mileage is 15 or less in true city driving and 18-20 on the highway unless you are driving steady 50-55mph where you might get 21.
 

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Discussion Starter #5
I've always done the mpgs by hand every tank since I bought it. Best I saw was 25.2 to Cleveland and back. Always hung right around 23-24 pure highway and I knew it was good for the vehicle at the time.

I've never had the valves adjusted since I've owned it at about 150k. It does not have a roof rack and seemingly everything is in its proper place, it doesn't have a bed cover, no rattles either.

I did just get an estimate over the phone on all 4 o2 sensors installed for $758 out the door. I think i will probably start there unless getting valves adjusted would be more beneficial?
 

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The 0420 are cat codes,not o2 sensors..
 

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2006 Ridgeline RTS in Steel Blue
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Personally I know I could do the upper two, A/F sensors which are commonly referred to as o2 sensors but they are actually Air/Fuel sensors. If the sensors have failed then the incorrect fuel trim information is going into the fuel management part of the OBD system. Unfortunately, that can cause the system to run rich, which can thereby damage the cats.

There are several options at this point. But if fuel economy is the goal, getting the emissions controls running correctly can improve fuel economy.

If I lived somewhere where there were no emissions requirements I would start looking at threads where some of the system has been bypassed and free flowing manifolds and less restrictive cats.

YMMV
 
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