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P0420 engine code

96K views 54 replies 28 participants last post by  speedlever 
#1 ·
i have 112000 miles on my rts, everything runs as it should and all of a sudden my check engine light popped up, telling me.... catalist blah blah blah bank 1, in the past that meant oxygen sensor, (pre-cat).... anyone had this issue.

i erasaed the code and it hasent popped up yet,
any advice would be great, thank
w
 
#2 ·
I have the same code, I needed to pass inspection....my mechanic told me I needed a new "bank1" cat. I took it to Honda they told me the same...I bought a new cat and the light still comes on.

I took it for inspection again and my mechanic (not Honda) told me that Honda replaced the wrong cat...in fact they replaced one that doesn't even have a sensor on it.

I am going to call them this morning about it.
 
#3 ·
P0420: Rear Bank Catalyst System Efficiency Below Threshold(Bank 1)
There is a test proceedure to see if the problem is intermittent or steady. If steady, the rear WU-TWC needs to be replaced (catalytic converter).
After replacement, the re-learn proceedure should be followed to reset the ECM.
Make sure all lectrical accessories are off (AC, lights radio, etc)
Reset the PCM with the HDS (if you don't access to the HDS, there is a manual method that requires disconnecting the battery)

Turn iginition to on for 2 seconds (dont crank the motor)
Start the motor and run at 3000 rpm until the radiator fan comes on.

Idle the motor for 5 minutes ( don't touch the gas pedal)

If the fan comes on again, dont count the time it is running as part of the 5 minutes ( so if the fan comes on for 30 seconds every 2 minutes, you will run for about 6 1/2 minutes total)
 
#4 ·
I'm not a Honda technician, but I was a Lexus technician. The cats rarely fail. 99% of the time when we got a inefficient cat code, it was the sensor. Oxygen sensor. If it came on immediately after the code was cleared, it was usually a short in the heating circuit. Change the sensor, and no more problems.
 
#7 ·
hmmm, well I am going to the dealer in an hour...the service woman told me that there is only 1 cat that can be replaced...and that's the one that was done.

I find it funny that there are sensors on the 2 warm up cats (that can't be replaced, according to her) but no sensors on the one they replaced.
 
#12 ·
well keep in mind, its winter, anywere it gets cold is switching to "winter gas". basicly alittle more alcohol, conbined with all this ethonol that internal conbuston engines just LOVE! is a contributing factor. i have come to the conclutsion at least in my case that its the cat, not a O2 sensor, because mine comes and goes. mostly after hard acceleration or during towing, if it was an O2 sensor it would always be on. (i have alittle experiance in the area, my cars have always had one problem or another):D

ima just go the cheap route weld on a cat myself, but thanks for all your imput i guess i have a honda im allowed one problem;)
 
#15 ·
Any opinion on using one of these devices to keep the CEL off: http://store.kteller.biz/product.as...&strPageHistory=search&numSearchStartRecord=1

If it can keep the light from coming on with no cat, it should surely keep it off if you do have a cat thats just tired. It basically moves the O2 sensor away from the direct exhaust stream thus it doesn't sense all the HC's so it won't trigger a P0420/P0430 code. Obviously if your cat has had a melt down it won't help but if its just triggering the code now and then from old age, it may help you put off replacing the cat if you need a emissions inspection.
 
#18 ·
My '06 ridgeline with 190,000 km's on it just posted this code today.
I cleared the code with my code reader but also noted that I have an Evaporative system monitor not responding.
I took the truck for a ride after clearing the code and it hasn't returned yet.
Not sure if these are related, might try the dealership to see what they have to say.
 
#20 ·
Update: After 1 week the light came back on for 1 day. The light has not been on since. I have been filling the RL consistantly since the 1st incident with premium.

Question: Has there been any damage done that would affect future engine performance? Would there be any reason to replace the cat or the o2 sensor?
 
#21 · (Edited)
Hey all- new member here. Got RTL with 93,993 miles on it and now getting the 420 code on bank 1. is there anyway to tell whether the downstream or upstream o2 sensor should be replaced, or should they be replaced in tandem? I wanted to this before investing in a new cat....was going to go with ngk sensors if available...are these any better than the bosch sets? thanks for your input!
 
#22 ·
Try switching just the upstream one with a sensor from bank 2. If you still get 420, then you know it's the downstream one on Bank 1. If you get a 430 (I think that's the one for Bank 2) then you know it's the upstream one (now) in bank 2. No need to pay for two if only one is bad - they aren't cheap nor returnable.
 
#25 ·
#26 ·
ok now have had this twice but last time reset it and changed gas to premium ran for around 2000 miles and just popped on again on the way home. Had decided to try 87 oct again about 2 tanks back and yesterday filled up with 93+. My dilemma is this if I take it to Dealer are likely to look at it charge me and then say it is a tank of gas after resetting it. They really do not like to do anything that may or may not be under warranty, and I thought there was an 80000 mile emissions warranty, but when looked up the info on fed site and honda states manufacturers usually cover it underpowertrain and Honda states 3yr 36000 for the powertrain. any body know of anywhere in particular that has the federal guidelines that state otherwise? I do not want to pay for a deductble on the extended warranty for them to do nothing per say. Or am I just worrying to much and it is just the winter mixture again. I wouldnt mind changing the sensors out and checking them if I could, but I have done the unthinkable ( I have not purchased a book!). LOL I have been meaning to but yeah I know. I would appreciate any suggestions. Or think I should try to argue with the dealer and see if they will cover the sensors/Cat? btw 62000 miles. thanks
 
#28 ·
Where I am in Virgina, or Taxginia as we call it, this is the scam they use. 1st they drive your car into the stall and if any lights are on you automatically fail but have to pay. Then you get a waiver to fix it. If they drive it into the stall and there are no lights but they connect to the computer and it shows a code, stored, whatever, automatic fail and repeat waiver process.

On older cars, usually pre 1996, they put the probe in your tailpipe (that sounds weird) and test the actual emissions, which is way more accurate IMO.

The old method gave you a range and if your emissions were in that range then you were fine. If not then a fail. The computer does not give you a snowballs chance in hell. A bad sensor can cause a fail when your car is actually withing established limits.

Just another way to screw ya!
 
#29 ·
Just got this code the other day along with some others. Went and bought a code reader that can reset them and did that the following day and drove all day today and it did not come back on.

One thing I noticed is typically my truck is driven all day and rarely goes out at night. The night it went on I went out and the truck was parked outdoors in temps below 20 degrees and it went on when I was on my way back home.

I've noticed a few oddities with my ridge (and 06 of which i'm the original owner) the last couple months when it's bitterly cold out. I'm seeing the airbag light go on and off also, when it warms back up it goes off again.

I'm thinking if this truck was kept outdoors regularly that I'd be having way more issues with it than I've had, which up until the last month was zero issues in 166,000 miles.
 
#30 ·
I have been getting this code for about six months now and the code reader indicates Bank 1. I am not sure if this is the CAT between the radiator and engine or the one between the bulkhead/firewall and engine. Can anyone tell me? I continue to reset it and it comes on every couple of weeks. Now, my Ridge has 138,000 miles on also. Do I need to stay with OEM CAT or is there a a pretty good aftermarket CAT I can use?
 
#31 ·
Bank 1 is the rear one.

 
#32 ·
You are Awesome speedlever! Thank you for the clear detail. Any comment on OEM replacement versus aftermarket?
 
#33 ·
Sorry, I don't know about that. My daughter recently had to have her Pilot's cats replaced in the 116k mile range and the mechanic (local guy, not a dealer) went with OEM over aftermarket... but I don't recall why.
 
#34 ·
Why doesn't that look like it's real easy to get up into? Or am I wrong?

I'm on day two of of no return of the light. Temps have been warm, around freezing and the truck has not been sitting not running in the cold for any extended amount of time. I don't know if i'm onto something or not, just an odd theory as when my light came on that my truck was used at a different time.
 
#35 ·
I suspect it's not easy to get to. I know the mechanic that did my daughter's Pilot said the rear one was a beyatch to do... or words to that effect. I bet the RL is similar.
 
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