P0401 and P0420 Check Emissions - Acura MDX Forum : Acura MDX SUV Forums
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post #1 of 18 (permalink) Old 1 Week Ago Thread Starter
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P0401 and P0420 Check Emissions

So my 2007 MDX is now conveniently throwing these codes less than 2 weeks before my annual emissions check. Last week the message came up but it went away after filling up with Premium gas and making sure the cap is on tight. This weekend it's been on since Friday evening. I added more premium gas and even changed the air filter but the message remains. This is a big problem for me since this car is the family's only vehicle. From what I read so far, I should focus on the P0401 code as this may be triggering the P0420 code. The P0401 points to the EGR valve. It may be dirty or it may just need to be replaced. I watched a video which shows the replacement of the valve. It looks kind of involved. Definitely not something I think I could do myself.
My question is this: If I should be able to get the message to go away will I still be able to pass the emissions test? Will the computer store those codes and cause me to fail? ill removing the battery clear the codes temporarily? Right now the car runs normally. I don't notice any lack of power or stuttering or surging when driving. I have a feeling that once I drive out the current tank of gas and fill it up the code may go away. I really need the car to pass inspection so I can renew my registration and legally drive the car.

Does anyone have any experience with this code? Any help would be appreciated.

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post #2 of 18 (permalink) Old 1 Week Ago Thread Starter
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Thanks for replying. I'm really hoping I can get past this emissions test. I'll take another look at the video for replacing and or cleaning the EGR and the port.

**Edit** There was a response that I was replying to but I no longer see it.
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post #3 of 18 (permalink) Old 1 Week Ago
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That was me it was not accurate! You have a few areas to check in terms of wire harness's and sensor harness's before moving onto replacing the actual EGR valve and sensor. If the EGR valve passage is blocked with carbon you will need to clean it out as well. If you get things working than yes pull battery cable to clear codes.


https://www.obd-codes.com/p0401
https://www.obd-codes.com/p0402
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post #4 of 18 (permalink) Old 6 Days Ago
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How many miles are on your 2007 MDX?
Have you noticed a loss of MPG (20%ish)?
Has your check engine light come on (I think so, because of the 0401 & 0420 codes)?

Without spending any money and just getting you thru the next emissions test:

Remove the cables from the battery for 2 - 3 minutes.
Write down the odometer value.
Drive the car and note how many miles, until the check engine light comes on.

I my case it was 7.3 miles. I located the emissions shop that I wanted to use and drove away from it 7.1 miles. I pulled over and pulled my battery cables for 2 - 3 minutes. I reconnected them and drove to the emissions shop. When I arrived, there was no check engine light and it passed.

Good luck, until you deal with your erg passages and clogged catalytic converter.
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post #5 of 18 (permalink) Old 6 Days Ago
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Quote:
Originally Posted by logisticalstyle View Post
So my 2007 MDX is now conveniently throwing these codes less than 2 weeks before my annual emissions check. Last week the message came up but it went away after filling up with Premium gas and making sure the cap is on tight. This weekend it's been on since Friday evening. I added more premium gas and even changed the air filter but the message remains. This is a big problem for me since this car is the family's only vehicle. From what I read so far, I should focus on the P0401 code as this may be triggering the P0420 code. The P0401 points to the EGR valve. It may be dirty or it may just need to be replaced. I watched a video which shows the replacement of the valve. It looks kind of involved. Definitely not something I think I could do myself.
My question is this: If I should be able to get the message to go away will I still be able to pass the emissions test? Will the computer store those codes and cause me to fail? ill removing the battery clear the codes temporarily? Right now the car runs normally. I don't notice any lack of power or stuttering or surging when driving. I have a feeling that once I drive out the current tank of gas and fill it up the code may go away. I really need the car to pass inspection so I can renew my registration and legally drive the car.

Does anyone have any experience with this code? Any help would be appreciated.
First question: Do you own a code reader? If not, where are you getting the codes from?

Second: What state are you in?

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post #6 of 18 (permalink) Old 6 Days Ago
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^ Maybe he has a TECH? the NAV shows OBDII codes in the 2G MDX.

To OP.. Try cleaning the EGR passages first in the intake manifold, You can use my DIY for the valve adjustment to clean the passages: https://www.mdxers.org/forums/74-sec...acura-mdx.html
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post #7 of 18 (permalink) Old 6 Days Ago
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^ Maybe he has a TECH? the NAV shows OBDII codes in the 2G MDX.
Thanks for the reminder. I never owned a Gen 2, and always used a scanner anyway. BTW: Can the built-in OBD2 on the NAV do a reset?

I agree that doing the EGR first is the best way to go. Once that is taken care of, a few tricks should get the cat problem past inspection.

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post #8 of 18 (permalink) Old 6 Days Ago
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No it can only store long term codes as a reminder/notes, To delete those "notes" you have to enter the "Secret NAV Menu" intended for techs.

But its in no way attached to ECU control, To delete/reset the actual code you have to plug the OBDII scanner or guetto remove them by unplugging the battery..

Deleting the actual code first WONT delete the "reminder/note" in the NAV.

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post #9 of 18 (permalink) Old 6 Days Ago Thread Starter
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Thanks for the replies. First I'll answer the questions and then give an update.

How many miles are on your 2007 MDX? I don't recall off hand but I am well over 200k
Have you noticed a loss of MPG (20%ish)? Not at all
Has your check engine light come on (I think so, because of the 0401 & 0420 codes)? The Check Emissions System message comes on and the engine symbol which I equate with a Check Engine Light

First question: Do you own a code reader? If not, where are you getting the codes from? I have two different code readers. 1 is a bluetooth version that I use with an app on my phone and the other is a cheap $10 unit I bought off of ebay.

Second: What state are you in? Georgia

Maybe he has a TECH? the NAV shows OBDII codes in the 2G MDX. Mine isn't a Tech, just a base model 2007 MDX.

**Update**
When my wife came to pick me up from the train yesterday evening the light didn't come on. We drove home, about 7 miles, and made a stop at the grocery store. When I got home I checked for a code using my bluetooth reader and app. Although the light wasn't on, the scanner picked up the same codes. I used the app to clear the codes and then went for a run to the store. Still no light. When I got back home I decided to disconnect the battery overnight so that I could be sure that any codes were really gone. This morning I get up and there was still no codes showing and no light on the dash board. I immediately went to get my inspection done and I still FAILED. It failed due to the on board computer not being READY. The technician asked me if I had recently had work done on the car. I told him no and explained that the light went off by itself last night. He told me that whenever the light is cleared, the computer has to reset and get into a ready mode before I can get tested. He advised me to drive the car for about 60 miles before I come back for my free re-testing. I looked at the print out and sure enough it passed every aspect of the inspection except for the Readiness test. M wife has to run a few errands today while I am at work so hopefully she can get enough miles on it so that I can try again tomorrow or sometime before that light comes back on. I'll post an update later.

One thing I did find out is my state can give you a 30 day extension if your registration is about to expire and you need more time to get the issue fixed.
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Thanks for the detailed update. I was going to mention the readiness system, but you now know about it. Some good info on the internet if you search. It is a good thing if you can get to understand how the monitors run under specific conditions, and in a certain order. It is also good to understand about "Pending" codes.

A trick I used for many years on customer vehicles with P0420 was to run all monitors EXCEPT the catalyst. At the time, in New York, the vehicle would pass with one monitor not set to ready, so the inspection would pass. I am not sure if this loophole still exists, as it based on Federal guidelines. Maybe a local shop can tell you about this. If the loophole has closed, there is another simple trick to legally sneak through with a failing catalyst. Also be aware that as the weather gets warmer, the catalyst efficiency increases, so you may have the catalyst test naturally pass as Summer approaches.

After you clean the EGR system, see if the P0420 still sets. Try to keep the fuel tank level between 3/8 and 7/8 full to allow the EVAP. test to complete.
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Every time you reset the ECU (Like by disconnecting the battery) the ECU has to relearn itself to proper mappings… This is done by simply driving! this is why is not recommended to clear the ECU and go do an inspection right away.

Another recommendation is to never do an Inspection while cold! drive your car in the highway for some time prior to taking it to inspection this will make sure all Cats/Sensors/Oils/etc are in operating temp ready for the test.

I live in California so I know the pains… Specially buying California ONLY Cats.

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I haven't gone back for a re-test yet. I found a PDF of the service manual on line that states that the system is not ready if the dashboard light blinks 5 times after I turn the key to the ON position. My light is still blinking. I've driven it over 200 miles now with a mixture of Highway and city driving. No Check Emission message or Check engine lights come on and my scanners don't ready any codes. My cheap ebay scanner also showed me that the the only readiness test that is incomplete is the EVAP monitor. I wonder, if I take it to the dealership for an emission inspection, can they get the system to Ready mode so that I can go ahead and pass this test? The dead line is my birthday which i this coming Wednesday. On Saturday I'll take it back to the original inspection shop for my free retest. If it fails there I don't think I will have any option other than to take it to the dealership.
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Here are some great videos to watch regarding getting rid of the P0401 & P0402 codes (EGR Valve)

There's a little something for everyone! 1st Generation MDX & 2nd Generation MDX

Hope this helps someone.
Good luck.


How to Clean Out the EGR Port on a 2004-2008 Acura TL (Code P0401) (just for an Acura TL)




HOW TO CLEAN EGR VALVE AND PORTS P0401 P0404 P0406




1st Generation MDX:
Acura MDX EGR Valve Replacement Guide

How to clean or change the EGR (exhaust gas recirculation) valve in a 1st generation 2001 to 2006 Acura MDX
https://www.paulstravelpictures.com/...ide/index.html





2nd Generation MDX:
2007 Acura MDX EGR P0401 (EGR VALVE DIY)



Parts list:
Genuine Honda EGR Valve (18011-RCA-A00) $199.75
https://www.acurapartswarehouse.com/...c118;et=1%2c2)

Genuine Honda Gasket, In. Manifold (17105-RCJ-A01) $28.45
https://www.acurapartswarehouse.com/...5-rcj-a01.html


Brake Parts Cleaner (2-3 cans)


Genuine Honda EGR Pipe (17181-RCJ-A00) $55.66
https://www.acurapartswarehouse.com/...1-rcj-a00.html


Genuine Honda Gasket Throttle Body (16176-RCA-A02) $1.21
https://www.acurapartswarehouse.com/...6-rca-a02.html


Genuine Honda Manifold Cover Gasket (17146-R70-A01) $23.55
https://www.acurapartswarehouse.com/...6-r70-a01.html
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I think I might be back in business. My wife just tested it today while I'm at work and the light isn't blinking anymore so that should mean the car is Ready. I'll check with my scanner when I get home tonight and then get tested in the morning.
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Here is the trick to get the Evap. monitor to run:

Fuel tank between 3/8 and 7/8 full. Near to half full is best.

Let the vehicle sit overnight.

Next day start up and let it run at idle in park for 2 minutes.

That should do it.
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