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Discussion Starter #1
I've already searched previous posts and none have definitive answers. My 06 throws a check engine light P0172 off and on as well as the VTM-4 off and on. Sometimes it has a hard time starting and other times no problems at all. A rough idle is also intermittent even by weeks at a time.

I've done plugs, coils, and battery but am hesitant to move forward with ordering parts like O2 sensors and various valve adjustments and parts till I really feel confident with the issue.

What say you guys?
 

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P0172 is usually a truthful code, as opposed to some others that really mean very little because they are a shot gun approach to diagnostics.

1. Inspect the Air Filter and its housing for debris from a rodent nest.
2. Try some fuel system cleaner, you may have a sticky injector.





Home Articles P0172 OBD-II Trouble Code: System Too Rich (Bank 1)
P0172 OBD-II Trouble Code: System Too Rich (Bank 1)
by Blake Griffin on April 13, 2016
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P0172 code definition?

P0172 is a trouble code that is set when the ECU senses that there may be too much gasoline present in the air-fuel mixture of the engine.

A proper air-fuel ratio of about 14.7:1 is vital to obtain maximum engine power and fuel economy.

What the P0172 code means

P0172 indicates that there is too much gasoline being detected in the exhaust gases exiting the combustion chamber. The ECU uses a number of instruments, such as the mass air flow sensor (MAF), oxygen sensors, and manifold absolute pressure (MAP) to monitor the air-fuel ratio of the engine.

Most routinely, the air-fuel ratio will be measured through the oxygen sensors calculating the amount of oxygen and carbon monoxide present in exhaust gases. The best air-fuel ratio modernly known to man is 14.7:1. This particular ratio was chosen because it was discovered to have the highest power output but lowest fuel consumption rate.

The ECU has the ability to slightly adjust the air-fuel ratio if it is rich. However, if the margin of compensation is too large, then a P0172 code will likely set. The term “rich” in this case means that there is too much gasoline and not enough oxygen detected in the air-fuel ratio of the engine.

What causes the P0172 code?

A dirty mass air flow sensor overstating the amount of air entering the engine which may cause excessive fuel delivery
A bad oxygen sensor
A leaking fuel injector allowing too much fuel to enter the combustion chamber
A faulty fuel regulator, which may not be regulating the pressure of the going to the engine as it should
A vacuum leak
A possible fault in the coolant system such as a stuck thermostat or bad coolant temperature sensor
Worn spark plugs


NOTE THAT THE UNDERLINED CAUSES ARE LESS LIKELY, AS THEY WOULD USUALLY AFFECT BOTH BANKS. Also, your 2006 doesn't have a Mass Air Flow Sensor.

Also, an exhaust leak before the Primary 02 sensor (Bank 1, Sensor 1) can cause a P0172


What are the symptoms of the P0172 code?

A Check Engine Light being set
Higher fuel consumption
Black smoke coming from the exhaust
How does a mechanic diagnose the P0172 code?

By performing a fuel pressure test
Using noid lights to check fuel injector pulse
Checking the vehicle for vacuum leaks
Inspecting the Mass Air Flow Sensor and Oxygen Sensors
Checking the Air intake system for clogging
Common mistakes when diagnosing the P0172 code

A technician may not inspect the coolant temperature sensor and cooling system. When the engine is cold, more fuel is added to help warm it up to a desirable temperature. If the coolant temperature sensor is not sending the proper signal there is a possibility that the engine ECU may assume that it is always running cold.

How serious is the P0172 code?

The car may not be able to pass a state vehicle inspection because of the P0172 code setting the Check Engine Light.

If the the air-fuel ratio is rich enough, a black smog will come out of the exhaust, which is harmful to the environment.

What repairs can fix the P0172 code?

A repair of a vacuum leak
A replacement of a faulty fuel injector, fuel pump, or fuel regulator
Replacement of an excessively restricted air filter
Replacement of the thermostat or coolant temperature sensor
A replacement of the spark plugs
A cleaning of the oxygen sensors and mass air flow sensor
Additional comments for consideration regarding the P0172 code

It is highly recommended to check the condition of the spark plugs and the operation of the coolant temperature sensor.

 

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Discussion Starter #4
That's a lot of good info.

Air filter is new as of 2 months ago but I'll check it again. I did a fuel system treatment about a month before it started showing these systems.

Considering what I've done, where should I go from here?
 

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Had a somewhat similar incident - 2005 MDX

I had a very strange problem after replacing the battery on a 2005 MDX. All my indicator lights were intermittently on/off - airbag, stability, VTM-4, fuel gauge would go to zero and then bounce back, oil pressure light, absolutely everything. The car would drive fine but it's un-nerving. The radio would turn off if I turned the headlights on. The main light in the instrument panel would flicker constantly. Everything, I mean every indicator light on the panel was intermittent on/off. I don't own a code reader. All I did was change the battery. I had a friend at a body shop do a quick check and the battery cables were fine. I called another acquaintance at his repair garage and he had no answer other than some cars need more time / drive-cycles to restore the ECU. I did some research online at various Acura user sites.

I found one possible fix: Turn off every light, radio, Garmin, etc. Turn the key to the on position but do not start it. Press the accelerator pedal to the floor for 30 seconds. Turn the key off and remove it. Release the pedal. --- It worked. It cleared everything. No more haunted electrical system. The radio stays on when it is supposed to. No stray indicator lights. Everything is normal.

You have nothing to lose. Try it.
 

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I had a very strange problem after replacing the battery on a 2005 MDX. All my indicator lights were intermittently on/off - airbag, stability, VTM-4, fuel gauge would go to zero and then bounce back, oil pressure light, absolutely everything. The car would drive fine but it's un-nerving. The radio would turn off if I turned the headlights on. The main light in the instrument panel would flicker constantly. Everything, I mean every indicator light on the panel was intermittent on/off. I don't own a code reader. All I did was change the battery. I had a friend at a body shop do a quick check and the battery cables were fine. I called another acquaintance at his repair garage and he had no answer other than some cars need more time / drive-cycles to restore the ECU. I did some research online at various Acura user sites.

I found one possible fix: Turn off every light, radio, Garmin, etc. Turn the key to the on position but do not start it. Press the accelerator pedal to the floor for 30 seconds. Turn the key off and remove it. Release the pedal. --- It worked. It cleared everything. No more haunted electrical system. The radio stays on when it is supposed to. No stray indicator lights. Everything is normal.

You have nothing to lose. Try it.
Your issue is quite obvious - weak original battery, continued electrical issue after new battery - alternator is dying. Unless you got really unlucky with a weak new battery.
 

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Funny you should say that. I checked the alternator before replacing the battery 2 months ago. It was providing the proper voltage to the battery and I assumed it was okay.

Fast forward to yesterday. I was driving normally. Nothing unusual was happening. When I drove home I put the gear in park and removed the ignition key and the car was absolutely dead. No lights of any kind, no radio, no fan, nothing electrical. And of course, it's not going to start without current to the ignition switch. I spent a lot of hours searching for an answer on the internet but I found nothing. This evening I came back to this site and find your post. Now it makes sense, I think, because I'm not a car expert. The alternator stopped (or very weakly) charging the battery to the point that now it's dead. Dead battery = no current to the ignition switch, no current to anything electrical. Wow! That makes sense. Tomorrow I'll check the alternator - Thanks!
 

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Discussion Starter #8
UPDATE:

I gave in and took it into the shop. My local Acura dealer said that they aren't sure what is causing it and recommended repairs that I have already done.

I'm thinking I'll do O2 sensors next, and just keep going till I find it and know that at least it's getting fresh parts. :mad:
 

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The O2 sensors (aft of converter) only detect catalytic converter efficiency and don't affect fuel trim. The upstream sensors are Air/Fuel sensors and much more expensive than O2 sensors.

Bank 1 is the rear bank so you could replace only the rear AF sensor.

If your scanner has some monitoring capability, the long term fuel trim (LTFT), and rear O2 sensor voltage can confirm if B1 AF sensor is responding correctly. Check for high negative LTFT (rich mixture trimmed to limit, perhaps negative 25-35%) and high (0.7v or higher) B1 O2 sensor voltage. This would indicate mixture is indeed rich and AF sensor is responding correctly. Also you can cause a false lean by adding air (pull vacuum brake booster vacuum line). LTFT should begin to come down (less negative) and B1 O2 sensor voltage should go low (< 0.2v).

If you confirm these tests you will gain nothing by replacing AF sensor and problem is due to excess fuel or air starvation on one or more cylinders (blockage). Air starvation seems unlikely but possible.

good luck
 

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Discussion Starter #10
The O2 sensors (aft of converter) only detect catalytic converter efficiency and don't affect fuel trim. The upstream sensors are Air/Fuel sensors and much more expensive than O2 sensors.

Bank 1 is the rear bank so you could replace only the rear AF sensor.

If your scanner has some monitoring capability, the long term fuel trim (LTFT), and rear O2 sensor voltage can confirm if B1 AF sensor is responding correctly. Check for high negative LTFT (rich mixture trimmed to limit, perhaps negative 25-35%) and high (0.7v or higher) B1 O2 sensor voltage. This would indicate mixture is indeed rich and AF sensor is responding correctly. Also you can cause a false lean by adding air (pull vacuum brake booster vacuum line). LTFT should begin to come down (less negative) and B1 O2 sensor voltage should go low (< 0.2v).

If you confirm these tests you will gain nothing by replacing AF sensor and problem is due to excess fuel or air starvation on one or more cylinders (blockage). Air starvation seems unlikely but possible.

good luck
Great advice, thank you. I'll check the numbers tomorrow and see what happens. I'll keep you all posted.
 

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Discussion Starter #11
Okay, next update. After looking over the live data, it looks like it's not the/a O2 sensor(s). Pics of live data below.

Also, it's showing P0171, which is the other bank. So now both banks are reading rich. It also has 4 pending codes, all misfires: 0303, 0304, 0306, & 0300.

So, fuel pump? Coolant Temp Sensor? What do you guys think?
 

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Valve adjustment is usually the culprit in 030X issues.

It's $300 with a local guy, see if the dealer will give you a better price.
 

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Discussion Starter #13
But those are just pending codes, most likely they only come on during extreme rich loads. I'm more focused on the 0171/2 codes.
 

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Posted pics don't indicate a problem that would set code P0171 or P0172. Suggest posting the freeze frame data for the set code to see what was happening at time of code setting.

Posted data indicate trending rich (negative LTFT) condition (at the moment of data capture) but show STFT is managing (0% STFT) to achieve desired A/F ratio (usually about 14.7/1). The codes (P0171 and P0172) are set when combination of STFT and LTFT for a bank exceeds some preset limit; usually about 25-35%.

Unlikely that new AF sensors will resolve problem.

Not sure if tight exhaust valves would cause P0171 or P0172, however at your mileage valve adjustment is likely indicated. I recently performed valve adjustment on my03 MDX (not missing) and found 3 exhaust valves slightly tight (< spec).

good luck
 

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I missed something on my first pass through your screen captures. Both equivalence ratios are indicating extreme rich condition. I suspect that an equivalence ratio of 1.99 is not possible unless something is wrong w/ AF sensor, AF sensor wiring, or connector (perhaps a short to ground, but both sensors is strange). This may be a default maximum value. Only way to know is to check directly w/ VOM or O'scope for values of AF sensor output voltage at the sensor connectors using a back-probe pin (T-pin).

I attach page from shop manual for P0171, P0172, P0174, P0175.

good luck
 

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That's one thing I really like about the Torque app - it lets you chart the output of your O2 sensors graphically - very handy when you're chasing an odd problem like this one. Of course, it only works on Android phones, but for less than $30 (for the bluetooth OBD dongle and Torque Pro app), you have the kind of technology only F1 teams had not that long ago.
 

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Discussion Starter #17
Okay, update (sorry for the zombie thread). I sucked it up and did the valve adjustment to see if that was the demon causing these problems. It's been several weeks now and no CELs, hesitation, or misfires. Idle is much better and my average MPG has gone from 14.1 to a whopping 15.2. Oh DANG! :D

If any future forum goers have these symptoms (or similar) refer to this thread as a reference!
 

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Valve Adjustment is one of the hardest thing to wrap around your head that you need when you need it.

I did that to a honda, spent $200+ dollars on parts I could change myself and poof, it was a $100 valve adjustment.

BTW XsV what did you spend on the adjustment? I spent $300 at my local shop.
 
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