2007 Honda Accord SE 2.4 liter keeps failing emissions…NOx too high

I’d start by looking at fuel trims to see if it’s running lean and figure out whats behind those 2 DTC?s Both of those could be where your issue is.

Please post gas Analysis… besides that, some basic scan data page would be very helpful. These would include graphed data of MAF, MAP, STFT, LTFT, RPM

Here is the NOx graph

I don't think cat is up to the task-quality issue. Is this direct fit or universal. If fuel trims are good, the cat looks like it's getting overwhelmed, not loaded correctly or big enough-again, your trims have to be tight though.

Here in California, I don't see IM240 failures, so I'm not familiar with diagnosing that particular test. Seeing how NOx is jumping up and down, I'd look closely at the A/F sensor, and the rear O2 sensor. I'm thinking wide mixture swings. How about collecting a graph of the sensors as you're traveling down the road at about 25 and 50 mph for 2 minutes at each speed?

What testing was done for listed dtc's specially for P0135. What brand and number was the Cat replaced?

Make sure your running honda upstream o2 and denso or ntk downstream. Ecm update.

Jeremy, I only use OEM or NTK on Honda, but I got burned once using NTK on a 2005 K24A4 Accord which uses the same federal emissions downstream sensor part number as the OP's 2007 Accord. I installed a new NTK downstream sensor (24647) for a heater code (it was a slam dunk diagnosis), but afterward a downstream sensor performance code would occasionally set after days/weeks/months of driving…

All combustion engines require good inputs to produce good outputs. I see an input problem described by the information you provided. Have the codes been cleared and then came back? O2 sensor circuit needs to be corrected. High NOX can be cause by excess lean mixture issues. Exhaust temps go high and so does NOX. I would start by cleaning and re gapping plugs (or replace them), then clean MAF…

Those dtc you have for knock sensor could be mechanical issues , the 02 sensor will not perform well with out the Heather portion not operating correctly besides that will fail emission for monitors o dtc present

OEM catalytic converter, right? If not, I'd start there.

Have you checked the distribution manifold for the egr? I have seen many plug up the further you get away from the egr valve. There are removable plugs to allow cleaning

I cleaned the manifold when I cleaned the EGR valve and it got better as I said. Went from 3 to 2.

Sorry missed that

Probably never had a valve adjustment, so I would do that first. Honda's valve clearances are best done cold. I was a Honda Tech for 20 years and from what I remember that could be the cause.

If the heater circuit is good and it needs a front sensor, you really should put a Honda sensor in, when I get these kind of problems the ATS e- scan can quickly get you thru fuel trim and converter issues, OE converters are a must , like it has been mentioned Honda's from this vintage and this 2.4 often have tight valves that need to be adjusted, but your trouble really sounds like a fuel trim…

Someone suggested valve adjustment… That is absolutely a possibility. With a lack of valve adjustment you will lack valve overlap and a introduction of EGR to the cylinder. properly adjusted valve clearances increase overlap and will improve EGR redistribution. To help in for valve overlap is correct we could reflect on the MAP voltage. Please tell us what MAP voltage is during a hot…

Did you put a factory catalytic converter on it? Did you put the correct O2 sensor in it? Did you repair the Knock sensor code? Is it still setting the codes? If you did not put a factory catalytic converter in it, I would start there. There is a reason California will not let us install aftermarket cats on some OBDII cars. They are the ULEV and SULEV cars. How much carbon is in the motor…

Michael, EGR rarely if ever fixes a modern vehicle IM240 NOx failure. Your vehicle is running too lean and your converter can't reduce NOx so you can't test the converter until you get Lambda under control. Give my office a call and we can bring it in and I will help you figure this one out.

Hi Randy, your comment about EGR repairs “rarely if ever fixes an IM 240 NOx failure” surprises me. I’m not challenging you but I’d be interested in the logic behind that statement. Happy Trails

That caught my eye too. I think he means that of all the causes for high nox that he sees, EGR issues are in the minority. I'm assuming they fix more mixture, VVT, and converter related problems than EGR problems for high nox complaint. A lot of modern vehicles don't have EGR valves now so that skews the trend as well.

This older model Honda has no vvt and has a very mild camshaft profile so an egr valve and system is most critical to low nox, small thinks like retarded timing, vacuum leaks, wrong o2 sensors or converters can greatly affect nox, I had some cases in the shop where cylinder heads were machined and the edges of the combustion chambers were not chamfered and the sharp edges cause hot spots which…

Tony, Rusty, I seriously meant what I wrote. I rarely give EGR a second thought on a NOx failure. Do you still believe that's why engineers put those little gadgets on the engine? :) When I do live presentations I like to disable EGR on at least 1 vehicle in front of the group and I yet to have seen NOx change much. Usually 0 - ½ gram per mile and sometimes up to 1 but that's unusual. My…

But Randy, what about those new fangled engines with variable valve timing, doesn't that create a built in EGR valve? If the VVT fails doesn't NOx go off the charts? lol No, I don't really need an answer, just being an axx. Eric