Acura MDX SUV Forums banner

1 - 20 of 32 Posts

·
Registered
Joined
·
111 Posts
Discussion Starter #1
2005 MDX Touring doesn't emit any weird rotten egg smells and only shows P0420 intermittently in winter/cold weather. We have no CEL/MIL in Summer/warmer weather. I haven't seen a noticeable drop in mileage or performance, since having this issue. From millions of posts I read, according to Honda/Acura techs, 99% of this code is the cat failing. I would like to be sure so I ordered an IR thermometer and OBDII dongle for my android. I will use Torque Pro to read voltage on O2 sensors and use the IR thermometer to read the temp in front of and behind the cat. That is if I can reach those areas. I have also read that you can use a shop vac and some soapy water to locate any possible leaks in the manifold or cat. I will also tap on the cat with a rubber mallet to see if I hear any part of the honey comb broken up.

If it ends up being the cat, I plan on removing and replacing it with this OEM cat:
CONVERTER, RR. PRIMARY for 2005 Acura MDX 5-DOOR|18290-RCA-L00 : Acura Parts | OEM Acura Parts | Factory Acura Parts

I will also use the OE gasket and any applicable fasteners I need. At ~$300 the cat is actually less than I was thinking it would be. From what I have read about Pilots and Ridgelines, you need to remove or move the CV Axle to gain access to the bank 1 cat. I do have an impact wrench, though I am wondering if I should get an air ratchet for this part. If I do need to remove the axle, I read I might need an additional tool for that. Never removed an axle, but I have changed brakes, calipers, and struts assembles before.

I look forward to getting this done as I want to drive this for another year and sell it as an honest person at a good price. I live in NY and I do not want to put a spacer or anything to fool the system.

My last worry is I wonder exactly why this failed, I had the timing belt, spark plugs, and other major maintenance done about 4 winters ago. I haven't seen any other MIL/CIL. I also changed it with Mobile 1 synthetic, since I have owned it. I used to use 87 octane, though this past winter I started to use higher octane to see if that fixed the issue as well as tried a bottle of injector cleaner w/ no avail. The light will go off at random times, then seems to come on during my 30 min commute to work. Storing it in the garage, seemed to help a bit, until it got really cold. I think temperature is key factor in this right now as metal tends to contract with colder temperature, then expands when heated. I wonder if their is a leak between the exhaust manifold and cat. It just seems very odd to see issues at only at ~40F or below.

What do you guys think?
 

·
Registered
Joined
·
1,750 Posts
My experience is the opposite - the cats seldom fail, but the O2 sensors are a maintenance item (the general rule is that they're suspect beyond 100,000 miles). It's a WHOLE lot easier to replace a downstream O2 sensor than a cat, so I'd seriously suggest doing that first if there are no performance issues (which could indicate a clogged cat, which does need to be replaced). There are a host of other possibilities, including a loose connection (common on cars that are driven on salty roads). But if it was my vehicle, first I'd check the output of the O2 sensor with my Torque app (or similar), and replace the O2 sensor first, just playing the odds.
 

·
Registered
Joined
·
111 Posts
Discussion Starter #3
My experience is the opposite - the cats seldom fail, but the O2 sensors are a maintenance item (the general rule is that they're suspect beyond 100,000 miles). It's a WHOLE lot easier to replace a downstream O2 sensor than a cat, so I'd seriously suggest doing that first if there are no performance issues (which could indicate a clogged cat, which does need to be replaced). There are a host of other possibilities, including a loose connection (common on cars that are driven on salty roads). But if it was my vehicle, first I'd check the output of the O2 sensor with my Torque app (or similar), and replace the O2 sensor first, just playing the odds.
Thanks, I will check it out, are you a tech or something? I will check the readings of the O2 sensor, if this OBDII reader will ever arrive. Amazon Prime lost it twice, so they are sending me another one....grr...

The sensor is about 1/4 of the price of the Cat. From what I read the O2 sensors have their own code.
 

·
Registered
Joined
·
1,750 Posts
I'm just a shadetree mechanic, but one who's been around the block a few dozen times (and have trouble-shot / fixed several cars with cat and/or O2 sensor problems before).

The P0420 code could be a bad cat or a bad sensor (kind of hard to tell from just the code). The Torque app I use on my Android phone (with a $20 OBD Bluetooth dongle) is great because it lets me do a real-time graph of the O2 sensor status and outputs. Really helpful for determining where the problem is. I can't recommend the app enough ($10 I think - best diagnostic money you'll ever spend if your phone will work with it - there are other options for non-Android phones that probably work well, too - though some cost more).

A lot of Amazon (and others') shipments are going missing this time of year - just the nature of the season.

The fact the sensor is 1/4 the price of the cat (or $30 or so from Rockauto.com) is good - but the real advantage is that they're about 2% of the effort of swapping out the cat. I did both of my upstream sensors on my (at the time) 170,000 mile car "just because" - my mileage was down a bit, and I considered it regular maintenance. I didn't change the downstream (post-cat) sensors just because there's no real reason to - the upstream (pre-cat) sensors will affect your fuel mileage if they go soft, while the downstream ones just sniff the exhaust and give you a binary good/bad output. If they don't fail, there's no reason to replace them, but they're cheap and easy, so it's worth a shot to do the suspect sensor in a case like yours.

Hope that helps...
 

·
Registered
Joined
·
111 Posts
Discussion Starter #5
I'm just a shadetree mechanic, but one who's been around the block a few dozen times (and have trouble-shot / fixed several cars with cat and/or O2 sensor problems before).

The P0420 code could be a bad cat or a bad sensor (kind of hard to tell from just the code). The Torque app I use on my Android phone (with a $20 OBD Bluetooth dongle) is great because it lets me do a real-time graph of the O2 sensor status and outputs. Really helpful for determining where the problem is. I can't recommend the app enough ($10 I think - best diagnostic money you'll ever spend if your phone will work with it - there are other options for non-Android phones that probably work well, too - though some cost more).

A lot of Amazon (and others') shipments are going missing this time of year - just the nature of the season.

The fact the sensor is 1/4 the price of the cat (or $30 or so from Rockauto.com) is good - but the real advantage is that they're about 2% of the effort of swapping out the cat. I did both of my upstream sensors on my (at the time) 170,000 mile car "just because" - my mileage was down a bit, and I considered it regular maintenance. I didn't change the downstream (post-cat) sensors just because there's no real reason to - the upstream (pre-cat) sensors will affect your fuel mileage if they go soft, while the downstream ones just sniff the exhaust and give you a binary good/bad output. If they don't fail, there's no reason to replace them, but they're cheap and easy, so it's worth a shot to do the suspect sensor in a case like yours.

Hope that helps...
I took a look under and I can see how the down stream looks easy to swap out, compared to wherever the upstream is. Are the O2 sensors from Rockauto just as good as OEM? I heard for Cats you really want to stick with OEM. Once I get the scanner, I will use Torque Pro w/ it and will post my findings here.
 

·
Registered
Joined
·
278 Posts
You can also use a thermal gun to see the temperature of the cat. It should be be higher at the outgoing side than the incoming side. I think eric the car guy on YouTube had a video doing this test on an acura vigor oe another sedan but I assume it's similar test for all cars.
 

·
Registered
Joined
·
962 Posts
Retired Honda/Acura tech here. My experience with these brands is that P0420 is always cat related, not sensor related. When sensors get out of range, they throw sensor codes. You are describing a classic loss of catalyst efficiency. That is why it is temperature related. Cats are always more efficient in warmer weather. As they age and become less efficient, they often show P0420 beginning in cold conditions.

Question: Why are you considering changing the cat? Do you have to pass a state emissions test?

FYI, loss of efficiency has no effect on vehicle performance. It just increases emissions somewhat.

Removing the axle on a lift, with the proper tools, is an easy job. Doing it on jack stands can be a headache. You need a large socket on a powerful air gun to remove the outer axle nut. Getting the lower ball joint stud apart from the knuckle is no easy job either. You will need a very large screwdirver or pry bar to pop the inner CV joint out of the transmission. You will also need a good torque wrench for reassembly.

If you do tackle the job, spray rust bust on all the nuts on the old catalyst a few times for about a week before doing the job, and make sure that the socket you use on those nuts is a 6 point, not a 12 point. Adding heat with a torch just before removing them can be helpful.
 

·
Registered
Joined
·
962 Posts
The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor). A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase. When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.

The Honda PGMFI system is smart enough to see improper sensor operation, and not confuse it for a cat problem. Not knowing other car brands, I cannot comment on them.

More details here:

http://www.totalcardiagnostics.com/support/Knowledgebase/Article/View/47/6/o2-sensors--catalytic-converter-diagnostics
 

·
Registered
Joined
·
111 Posts
Discussion Starter #9
Retired Honda/Acura tech here. My experience with these brands is that P0420 is always cat related, not sensor related. When sensors get out of range, they throw sensor codes. You are describing a classic loss of catalyst efficiency. That is why it is temperature related. Cats are always more efficient in warmer weather. As they age and become less efficient, they often show P0420 beginning in cold conditions.

Question: Why are you considering changing the cat? Do you have to pass a state emissions test?

FYI, loss of efficiency has no effect on vehicle performance. It just increases emissions somewhat.

Removing the axle on a lift, with the proper tools, is an easy job. Doing it on jack stands can be a headache. You need a large socket on a powerful air gun to remove the outer axle nut. Getting the lower ball joint stud apart from the knuckle is no easy job either. You will need a very large screwdirver or pry bar to pop the inner CV joint out of the transmission. You will also need a good torque wrench for reassembly.

If you do tackle the job, spray rust bust on all the nuts on the old catalyst a few times for about a week before doing the job, and make sure that the socket you use on those nuts is a 6 point, not a 12 point. Adding heat with a torch just before removing them can be helpful.
I live in NY, so we have CA emission standards. I am planning on selling this vehicle within a year or so. Granted I could sell it and have the person deal with it, during the following winter. My inspection is up in January, so it is always pretty cold, though the past 2 years I was able to bring it in when the light was off for a quick inspection. With these symptoms, do you think there is anything wrong with the car that could have caused the Cat to fail? For the most part, from what I have read, Cats usually don't fail on their own. I have dropped so almost the value of the vehicle into this car, when the Tranny went. I put on new tires a month before that. I went ahead this fall and put on a new caliper and new rotors/pads all around.

From what you are saying and from what I have read from other Techs it is going to be the Cat. I guess other cars don't have as smart of an ECM and might allow for a lazy o2 sensor, w/o throwing a code for the o2 sensor? I have to throw money at a problem and that is why I wanted to make sure I properly diagnose the issue. Though from what you are saying, I can't figure out how it could be anything else.

I bought a larger compressor, impact wrench, and 6pt. metric impact sockets for replacing my wife's strut assembles on her Avalon this summer. I also have a breaker bar and various other tools. I heard of people just moving the wheel one way, instead of removing the axle. I will spray the nuts as you suggested, I tried that with my wife's jam nuts on her tie rods, though they had to replace them as they were seized. The larger bolts for the struts came out easier than I thought, the control arms were a bit fun. Seems like the smaller the bolt and the lower it is, the harder it is to remove. Got to love salt! I few places quoted me about ~$300+ for the labor, if I provided the ~$300 part. It just hurts spending more money and I also enjoy doing things myself.

My biggest concern other than removing the axle, is what caused it to fail?
 

·
Registered
Joined
·
432 Posts
Much respect, Hostage, for doing your part as a good human and not screwing over the next owner of your MDX.
 

·
Registered
Joined
·
111 Posts
Discussion Starter #11
I got my OBDII wifi adapter and Torque Pro. My wife and I carpool most of the time as we work .5 miles away, so it gave me some time to futz with it. It took me about 15mins to figure out how to get it working. It isn't really showing as many stats as I was hoping. According to Torque it lists available sensors that the ECU can read. It didn't have as many O2 sensors as I was hoping it showed the following among other things. I am unsure if I can get the info for what I was hoping for as I guess the vehicle is more limited than the scan tool or OBDII adapter I have? Again I am very new to this and I am still figuring out Torque Pro. It seems it is a lot more for people who want to race, instead of diagnostics.

Also forgot to mention I see this:

TID:$03 CID:$01
Low sensor Voltage for switch time calculation

Min: 150
Current:868

It shows it in green with a check "Ok", I guess it is working and I need a better understanding of this tool.
 

Attachments

·
Registered
Joined
·
1,750 Posts
Hmmmm... must be a different version of Torque Pro than I have. I could only get to the list of available items by going into the "add display" option - the available ones were in blue, as I recall.

I'll try to see what my downstream O2 sensor monitoring looks like - I've never HAD to use that for my MDX, but have used it on a number of other cars over the years. It really is a great too, and it's nice to put together a "road trip display" with all the sensors you would use to keep an eye on things going on under the hood. I wish I could monitor more of the transmission with Torque, but I always have the option of using my HDS clone for that (though it's not really something that's convenient to use "just driving around".

FWIW, I don't want to contradict someone who was a pro mechanic on Hondas and Acuras, but on every other car on earth, it's not at all unusual for an O2 sensor to fail.
 

·
Registered
Joined
·
111 Posts
Discussion Starter #14
I can modify this to remove and add other things like RPM, distance traveled, etc or any other usefull data. The only thing is it looks like I can only see the voltage of 2 o2 sensors, Bank 1 & 2 for sensor 2.

From what I thought the o2 sensors for sensor 2/down stream was supposed to show fairly strait line for a good cat, though in this, it looks like they are everywhere. Though the sensor 2 could be for a different sensor 2 or something else that I don't know about. I am good with IT related stuff and figuring out how things work, though just don't have the back ground knowledge to interpret things.
 

Attachments

·
Registered
Joined
·
1,179 Posts
Equivaence ratio is an indicator of AF sensor results (Upstream sensor) and is fine at near 1.

The two downstream (of cat) O2 sensors indicate performance of catalytic converter. P0420 is fault for rear (bank 1) cat and your bank1 O2 voltage has numerous voltage swings. Also your scanner is likely missing some voltage swings and peak values due to long update time step. It appears to be consistent w/ P0420 code. The shop manual does not specify the conditions (Number of voltage swings per unit time) leading to P0420 being set.

good luck
 

·
Registered
Joined
·
111 Posts
Discussion Starter #16
Equivaence ratio is an indicator of AF sensor results (Upstream sensor) and is fine at near 1.

The two downstream (of cat) O2 sensors indicate performance of catalytic converter. P0420 is fault for rear (bank 1) cat and your bank1 O2 voltage has numerous voltage swings. Also your scanner is likely missing some voltage swings and peak values due to long update time step. It appears to be consistent w/ P0420 code. The shop manual does not specify the conditions (Number of voltage swings per unit time) leading to P0420 being set.

good luck
I took a sample for the whole time, instead of just the short one I first listed. It looks towards the end the Voltage for the second one is even more crazy towards the end.

Edit: I added the Short term fuel trim values. It looks like my bank 1 values are running a bit lean, compared to bank 2. Could this cause the degradation of my cat? If so what is causing it?
 

Attachments

·
Registered
Joined
·
1,179 Posts
Both banks are slightly lean, which may indicate something or not. LTFT's indicate a trend (too much air/fuel or lack of same). Equivalence ratio around 1 indicates fuel control is achieving desired AF ratio.

good luck
 

·
Registered
Joined
·
962 Posts
Hostage: Can you get a graph of only B1S1 and B1S2 readings? That would indicate the health of the B1 cat. You need to be comparing input vs. output of just the one cat., not a comparison between both cats.

Also, if you are not aware, looking at as few parameters (data streams) as possible increases resolution of the ones that you want to see. It's a bandwidth limitation in low speed multiplexed systems.

As far as failure reasons, it was not uncommon to see vehicles of your vintage have catalyst failures in the 125K-150K mile area. They do wear out in time, just like all other components.
 

·
Registered
Joined
·
962 Posts
For further education, this is a good video source. He tends to be a bit long-winded, but he knows his stuff - as opposed to 98% of the idiots on youtube.

https://youtu.be/vyVnhCIMDnw

The important point he makes is that a catalyst with good waveforms from the O2 sensors can sometimes fail the oxygen storage test that the OBD2 system actually uses to compute efficiency, and possibly throw a P0420/P0430.
 

·
Registered
Joined
·
962 Posts
Why oxygen storage is important to the operation of three-way-catalysts:

Since 1981, “three-way” (oxidation-reduction) catalytic converters have been used in vehicle emission control systems in the United States and Canada; many other countries have also adopted stringent vehicle emission regulations that in effect require three-way converters on gasoline-powered vehicles. The reduction and oxidation catalysts are typically contained in a common housing, however in some instances they may be housed separately. A three-way catalytic converter has three simultaneous tasks:

Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O.
These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. This point is between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline. The ratio for Autogas (or liquefied petroleum gas (LPG)), natural gas and ethanol fuels is each slightly different, requiring modified fuel system settings when using those fuels. In general, engines fitted with 3-way catalytic converters are equipped with a computerized closed-loop feedback fuel injection system using one or more oxygen sensors, though early in the deployment of three-way converters, carburetors equipped for feedback mixture control were used.

Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and lean (excess oxygen) conditions. However, conversion efficiency falls very rapidly when the engine is operated outside of that band of air-fuel ratios. Under lean engine operation, there is excess oxygen and the reduction of NOx is not favored. Under rich conditions, the excess fuel consumes all of the available oxygen prior to the catalyst, thus only stored oxygen is available for the oxidation function. Closed-loop control systems are necessary because of the conflicting requirements for effective NOx reduction and HC oxidation. The control system must prevent the NOx reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage material to maintain its function as an oxidation catalyst.

Three-way catalytic converters can store oxygen from the exhaust gas stream, usually when the air-fuel ratio goes lean. When insufficient oxygen is available from the exhaust stream, the stored oxygen is released and consumed. A lack of sufficient oxygen occurs either when oxygen derived from NOx reduction is unavailable or when certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to supply oxygen.
 
1 - 20 of 32 Posts
Top