92 Accord EXR – Code 1, 41, 43

Hi RichWhitehead,

Interesting conditions regarding NOx (oxides of nitrogen) and CO (carbon monoxide). I am sure Eric will be licking his chops when he reads your post. Here are a few comments:

1. Based on code 41, the oxygen sensor would appear to need replacing.

2. Based on the gas analysis, were HC, O2, and CO2 also measured? If so, what were their readings please?

NOx is typically formed when the combustion chamber reaches temperatures greater than 2,300 degrees F. Check to make sure you have proper coolant flow and that your thermostat works. The EGR also helps to lower the combustion temperature by supplying exhaust fumes (hence less gas is being burned in the combustion chamber). I believe Eric mentioned this was a common occurrence with a plugged EGR (http://www.ericthecarguy.com/videos.aspx?vi=d8N-SE047VY)
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3. The first part of the catalytic converter (Rhodium coated honeycomb) takes the NOx gases and reduces them to N2 and O2. The generated O2 gas aids complete combustion (oxidation) of any HC or CO in the second part of the catalytic converter (Palladium coated honeycomb), yielding H2O and CO2.
Hey…I am putting my Chemistry background to use!

If the first part of the converter is no longer working, elevated levels of NOx will be seen, and there will not be generated O2 gas from the NOx reduction. Thus, any CO present in the exhaust would not be oxidized properly. You could have a combination of a bad O2 sensor, causing an incorrect air:fuel ratio (rich condition) along with a bad converter.

4. A faulty MAP could also produce a rich condition. However, given the info above, I would tend to lean towards the O2 sensor.

5. How many kilometer is on the converter? Keep us posted.

Thanks for the updated information. As inxs and twiggy02919 mention, confirm the connections and operation of the oxygen sensor. Does it cost an additional fee for a retry of a failed emissions test in Canada?

Your car has only one O2 sensor. Accords started having two O2 sensors in 95 for the V6 and 96 for the 4-cylinder.

There are several codes for the O2 sensor for different problems with the sensor. One code is for the internal heater of the sensor. The other code is something wrong with the signal from the O2 sensor.

I was almost positive I commented on this the other day, it all kind of runs together after a while.I:| Anyway it does sound like an O2 issue or at least that’s where you want to start. Anytime you have a heater code it usually means you need an O2 but be sure to check the wires just to be on the safe side as I’ve seen more than one occation where the wires got pulled out of the back of the connector. After you get the O2 in if you still fail you might want to check for vacuum leaks as they are a common cause of O2 codes, beware of exhaust leaks before the O2 also as this will also throw off the readings. Good luck.

Quoted From inxs:

All three codes are pointing towards a problem with the O2 sensor or the wiring. I would check the wiring first.

I would make sure that the O2 sensor is still plugged in. If it is, unplug the O2 sensor and see if there is any oil or corrosion on the pins in the electrical connector. There are some tests you can do on the oxygen sensor if you have a volt meter. Check for any damaged wiring on the sensor or the harness.

The emissions numbers are likely related to these codes. Once you eliminate the codes, then you can analyze the emisisons.

FYI, high NOx levels by itself is typically due to clogged EGR ports on the intake manifold. Google T2T013.pdf and you will find a good procedure on how this is done on a 90-93 accord. The first hit called TSB 013 on the tegger.com site (an excellent site for general honda diagnostics) is what you want to download. Diagnose those codes before doing this.

I agree to start with replacing the O2 but there may be other issues with the EGR or cat as inxs mentioned, personally I think your EGR passages may be clogged as well. I would start with the O2, reset everything and redo the test to see where your at. Keep us posted.