P0172 P0175 - System Too Rich - Troubleshooting Steps

TheJoeFletch · May 18, 2024

TLDR; should I just start with cleaning the MAF sensor? Do I need to record anything else besides 4g/s on the MAF sensor before proceeding?

Car

2011 Honda Odyssey
Original owner
129,750 miles
VCM Muzzled

I overanalyze things and try to document as much as possible (I try to use OdyClub for all of my Odyssey issues). So hang in there with me with all of this information!

I have an ODBII reader and the Torque app (I also have another handheld reader if needed).

I have the both P0172 P0175 codes on my car. Showed up about 1-2 weeks ago and didn't get a chance to troubleshoot it.

Research shows that it could be the Mass Air Flow (MAF) sensor or an Oxygen Sensor.

Cleaning the MAF sensor seems like a quick and cheap potential fix. But before doing that, any suggestions on what I should record before proceeding? Or is there no harm in preventatively cleaning the sensor?

I have seen a few YouTube videos where they remove the connector to the MAF to see if the car stalls indicating that the MAF is good. Is it worth doing this?

From Torque.

If I recall correctly, the Evaporative System always showed incomplete in Torque. So I do not think that this is a valid test from Torque.

The O2 Sensor is showing "complete"; not too sure what that means but could this be a false-positive?

At idle, the MAF is showing about 4g/s.

All of the tests passed.

Except for these here. I don't know if the EVAP monitor is available on my car.

TheJoeFletch · May 18, 2024

Do you think, that this is the problem? There's also a tear on the other side.

2011.2017.odyssey · May 18, 2024

Considering the MAF has been exposed to unfiltered air for who knows how long, I think you have your start point.

Get a new tube, dealer or big box carry them, clean the MAF the big box stores will have the cleaner in a can, also do the throttle body cleaning.

MrRangerZr1 shows the procedure on his youtube channel.

TheJoeFletch · May 18, 2024

2011.2017.odyssey said:
Considering the MAF has been exposed to unfiltered air for who knows how long, I think you have your start point.

Yeah, makes sense. With the break in the tube, do you think it is possible that there could be further concerns that come out of this issue? I do have a decent drive coming up. Just wondering if I should not take this car.

2011.2017.odyssey said:
Get a new tube, dealer or big box carry them

I have one ordered from Advanced Auto Parts. It is ready for pickup.

2011.2017.odyssey said:
clean the MAF the big box stores will have the cleaner in a can

I bought the MAF / Throttle Body cleaning kit from Walmart earlier this week.

2011.2017.odyssey said:
also do the throttle body cleaning.

MrRangerZr1 shows the procedure on his youtube channel.

This video? 2005-2010 Honda Odyssey Throttle Body Cleaning

For reference, I also found this on his channel. Honda Odyssey MAP Sensor Replace & Clean DIY

Thank you for the reply and the insight on this!

2011.2017.odyssey · May 18, 2024

The reason it tore is more concerning, likely VCM related.
Tube replacement and cleaning of the MAF clear the codes, is likely all you need.

That throttle body cleaning video is good enough to follow, His Honda Civic one is also good.
The second video on the MAP doesn't apply.

When you remove the intake boot and airbox cover, the MAF is right there inside the tube opening on the cover for you to spray.
Dont use any cleaning tools on it, just douse it with cleaner and let it air dry.
This fellow shows cleaning it by removing it, which isn't necessary in most cases.

The toothbrush method on the throttle body with a good rag, will get the dirt off the plate and throttle body.
just be gentle with the plate cleaning.

TheJoeFletch · May 18, 2024

2011.2017.odyssey said:
The reason it tore is more concerning, likely VCM related.

I don't follow this. Why would the VCM cause it to tear?

2011.2017.odyssey said:
When you remove the intake boot and airbox cover, the MAF is right there inside the tube opening on the cover for you to spray.
Dont use any cleaning tools on it, just douse it with cleaner and let it air dry.

Got it.

2011.2017.odyssey said:
This fellow shows cleaning it by removing it, which isn't necessary in most cases.

Since I have to take the boot out, I can probably leave it in the hood to clean it. But that will be a decision when I am working on it.

2011.2017.odyssey said:
The toothbrush method on the throttle body with a good rag, will get the dirt off the plate and throttle body.
just be gentle with the plate cleaning.

Will do. Thanks again.

oldskewel · May 18, 2024

Great debugging info here.

The intake tube can be a VCM victim indirectly. The VCM causes rough running, which kills the engine mounts, which allow too much engine rocking, which flexes the tube too much, leading to those cracks. But I had the exact same cracks in my intake tube at around 145k miles, even having been muzzled for a long time. Vs. never having that failure on my '99 Odyssey at 240k miles. So, the material may be weaker. Not a big deal. Cheap and easy replacement.

The throttle body will be easily accessible for cleaning when the tube is off.

Full agreement with all of @2011.2017.odyssey 's comments. The MAF and MAP are different. The MAF sensor is very delicate, so be sure to not touch or damage the thin film / sensor wire.

But I would not expect fixing the tube to fix your problem. A torn tube like that will let in unmetered air (air that gets sucked in due to Venturi effect, after most of the intake air gets measured as it flows past the MAF), so you'd have extra air. So, then the nominal fuel injection amount would result in a mixture that has less fuel than it should (perfect would be stoichiometric, a mass ratio of about 14.7 parts of air to 1 of fuel).

Your readings there show AFR (c) and (m) of slightly less than 14.7. Do you know if the c is for calculated (prob based on the MAF and calculated fuel injection) and m is for measured (inferred from the A/F sensor readings)? They are shown as green and are close enough to 14.7 that it appears right then, nothing was wrong.

So, at torn tube would make your mixture LEAN, not RICH as you are getting. That would be P0171 and P0174 for banks 1 and 2.

The upstream O2 sensors are the A/F (air - fuel mixture) type, which provide a feedback signal for the fuel injection to optimize the air fuel ratio. I don't know exactly how the car decides to set those codes you got, but it probably finds itself needing to inject less fuel than it expected to maintain the A/F readings from the A/F O2 sensors on banks 1 and 2. Those sensors are downstream of the engine, and upstream of the bank1/2 cats.

So I'd still do everything you're planning to do. It's all good, needed, and should not hurt. But I will not be surprised if you find those codes still around.

The EVAP readiness (BTW, the only one not required for CA smog) can take a really long time to become ready, so I would not worry about that. Good that you've got a few different OBD2 tools. They can give different results on things when you really try to get into a not-obvious problem.

A general debugging tip here - your codes are showing for both banks. So it is more likely that whatever root cause you've got is something that affects both banks rather than just one. (Assumptions here - that you've got only one root cause, and that it is not likely that the same failures would occur independently on both banks - are probably true, but may not be). So something related to fuel pressure or air intake (which affects both banks equally) would be more likely than an O2 sensor (which is an independent sensor on each bank - although they could both be damaged by the same engine problem, so it is not impossible).

How long ago was the engine muzzled? Maybe some damage was done.

Other than the codes, does it run well? If you track your MPG, has anything changed?

Just a guess here - have you noticed any pressure release when opening the gas cap? Just wondering if you do have an EVAP problem (system that regulates vapor pressure in your fuel tank), maybe your tank is over pressurized, which may lead to higher fuel pressure, which may lead to too much fuel being injected, giving a rich mixture. Ideally, to confirm this, you would have a situation where your OBD2 is showing a problematic AFR, then you open the gas cap and see it go to normal. Problem with these codes is that they get set, even when the problem comes and goes - as they should, but it can be confusing.

TheJoeFletch · May 18, 2024

oldskewel said:
The intake tube can be a VCM victim indirectly. The VCM causes rough running, which kills the engine mounts, which allow too much engine rocking, which flexes the tube too much, leading to those cracks. But I had the exact same cracks in my intake tube at around 145k miles, even having been muzzled for a long time. Vs. never having that failure on my '99 Odyssey at 240k miles. So, the material may be weaker. Not a big deal. Cheap and easy replacement.

oldskewel said:
How long ago was the engine muzzled? Maybe some damage was done.

I have had the engine muzzled since 2018. Details below but documented here.

June 2018: On a 1,000 mile road trip with the family. Check engine light comes on. Engine vibration. 87,600 miles. I was able to get it to the dealer. Found OdyClub. Typical VCM issue based on what I have read here. Replaced piston rings and spark plugs (among a couple of other things). After this repair, I installed a crappy VCM muzzle. ECO mode is limited to traffic conditions.

oldskewel said:
Full agreement with all of @2011.2017.odyssey 's comments. The MAF and MAP are different. The MAF sensor is very delicate, so be sure to not touch or damage the thin film / sensor wire.

I missed the difference but I understand the process for cleaning.

oldskewel said:
But I would not expect fixing the tube to fix your problem. A torn tube like that will let in unmetered air (air that gets sucked in due to Venturi effect, after most of the intake air gets measured as it flows past the MAF), so you'd have extra air. So, then the nominal fuel injection amount would result in a mixture that has less fuel than it should (perfect would be stoichiometric, a mass ratio of about 14.7 parts of air to 1 of fuel).

Oh damn. haha

oldskewel said:
So, at torn tube would make your mixture LEAN, not RICH as you are getting. That would be P0171 and P0174 for banks 1 and 2.

Yeah, that is a good point.

oldskewel said:
So I'd still do everything you're planning to do. It's all good, needed, and should not hurt. But I will not be surprised if you find those codes still around.

Damn again...

oldskewel said:
Other than the codes, does it run well? If you track your MPG, has anything changed?

It feels fine to me. No out of the ordinary vibration or feeling while driving. I tracked my MPG for the longest time and it was the same value forever. I stopped quite some time ago. Looks like I should never have stopped.

oldskewel said:
Just a guess here - have you noticed any pressure release when opening the gas cap?

No, I have not noticed this.

Thank you for the detailed reply! I'll keep an eye on it after making this fix.

2011.2017.odyssey · May 18, 2024

TheJoeFletch said:
Since I have to take the boot out, I can probably leave it in the hood to clean it. But that will be a decision when I am working on it.

when you unclip the top section from the airbox, and unscrew the clamp on the intake tube, the top cover comes off so you can clean it on the bench / over some newspaper or rags.

WiiMaster · May 18, 2024

Even my non-VCM Ody has had this failure. Whenever motor mounts wear out on the J series, regardless of how it happened, this tube is one of the first things to go.

But since my Odyssey is not a MAF vehicle, it did not have any other symptoms.

oldskewel · May 18, 2024

So 88k unmuzzled, now at 130k. Makes sense that the intake tube went a little early here. You might take that failure as an early indicator of bad engine mounts too - keep an eye on them.

The core problem of the rings in the engine will fix itself once muzzled, but exterior damage - mounts, intake tube, possibly exhaust issues with O2 sensors and cats, will not self repair.

BTW, when my intake tube was found to be cracked at 145k miles, I had no symptoms and no codes. I just happened to notice it one day. I posted pics on here somewhere, and it was pretty well cracked in both locations, but still no codes.

TheJoeFletch · May 18, 2024

oldskewel said:
So 88k unmuzzled, now at 130k. Makes sense that the intake tube went a little early here. You might take that failure as an early indicator of bad engine mounts too - keep an eye on them.

What would be the signs of bad motor mounts? Excessive vibration?

oldskewel said:
The core problem of the rings in the engine will fix itself once muzzled, but exterior damage - mounts, intake tube, possibly exhaust issues with O2 sensors and cats, will not self repair.

Anything proactive I should be doing here? Or just wait for a failure? (Which I may already have.)

oldskewel said:
BTW, when my intake tube was found to be cracked at 145k miles, I had no symptoms and no codes. I just happened to notice it one day. I posted pics on here somewhere, and it was pretty well cracked in both locations, but still no codes.

Which could mean that I have something else going on here. Thanks for the feedback.

TheJoeFletch · May 18, 2024

WiiMaster said:
Even my non-VCM Ody has had this failure. Whenever motor mounts wear out on the J series, regardless of how it happened, this tube is one of the first things to go.

In all of my research around VCM and muzzling, I never noticed any mention of the tube failure. I was aware of the motor mounts, but not the tube.

WiiMaster · May 18, 2024

TheJoeFletch said:
In all of my research around VCM and muzzling, I never noticed any mention of the tube failure. I was aware of the motor mounts, but not the tube.

It is mentioned in the megathread.

TheJoeFletch · May 19, 2024

Damn. I can't seem to get the small metal hose at the top back into the rubber duct. No amount of forcing it can get it to move. Any suggestions? Silicone based lubricant? Or is that suggested on the intake of the engine?

TheJoeFletch · May 19, 2024

TheJoeFletch said:
Damn. I can't seem to get the small metal hose at the top back into the rubber duct. No amount of forcing it can get it to move. Any suggestions? Silicone based lubricant? Or is that suggested on the intake of the engine?

I finally got it. Order of operations matter. This tube needs to be attached after the air filter and throttle body are connected. I really had to force the tube in.

phattyduck · May 20, 2024

Once that intake tube is fixed, check the LTFT and STFT (long term fuel trim and short term fuel trim) during all driving conditions. There will be a pattern there that will be helpful for diagnosis.

This may be a leaking fuel injector, it may be some other sensor not working, etc.

-Charlie

TheJoeFletch · Jun 28, 2024

After replacing the tube, we have driven the car over 700 miles. No issues. Thank you all for your support!

egads · Jul 1, 2025

A Data point (that I will update if anything changes)
I got these two codes 180 miles from a fill up of cheap gas. Came on after a quick pee stop. Drove the rest of the way home, including a mountain pass (aggressively) without issue. Got the codes read (and MAF sensor cleaning) the day after. The fill up from the cheap place was an almost full 18+ gallons, something my 2015 EXL is not used to, being a Top Tier queen.
Air intake does not look to be in bad shape, engine muzzled at 28K, currently at 82K. OEM filter changed about 4K ago. So if you get these codes at lower miles without the obvious tear, it could just be shitty gas. I should take my own advice and not be cheap.

P0172 P0175 - System Too Rich - Troubleshooting Steps

TheJoeFletch

TheJoeFletch

2011.2017.odyssey

TheJoeFletch

2011.2017.odyssey

TheJoeFletch

oldskewel

TheJoeFletch

2011.2017.odyssey

WiiMaster

oldskewel

TheJoeFletch

TheJoeFletch

WiiMaster

TheJoeFletch

TheJoeFletch

phattyduck

TheJoeFletch

egads

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