Looking for P0172 writeup

[psraff]

Hey guys... I've started throwing the famous P0172 Error and even though my Scangauge will clear it, it keeps returning every couple of days so I know it's not a freak thing.

I've been searching for days on info and I'm hoping to find a good write up explaining the who's and what's on this error. As we all know, multiple pieces could cause this to happen, and even multiple different combinations of them as well making this very hard to track down.

Is there a write up here, or on another thread that anyone knows about that has a good starting point (most common cause, or most obvious cause) so I'm not running around in circles and spending money on wasted parts? Besides poor fuel mileage, I can't see any difference in the truck running.

Thanks everyone!!!

 

[ferkkila]

P0172

This error code was driving me crazy too on my 1999 4runner. The code was very intermittent and didn't really seem to be affecting the way it ran at all. I could drive 200 miles and not see the code then shortly after I start it I would see the code again. I kept my tool to clear the code in the car because the CEL always drives me crazy. I did find that after I cleaned the MAF sensor it would seem to go longer without seeing the code. I finally broke down and bought a $25 Chinese MAF sensor just to see what it would do. I am happy to say I have not seen the code since I replaced the part. I don't know how long this cheap Chinese sensor will last but right now it's working fine and no more CEL. I was also looking high and low for an answer to this issue. Hope this helps.

 

[TucsonMike]

p0172 question

Sorry to revive an old thread but had to sign up again due to inactivity. I do have a 4runner, but my issue is with my Sequoia and since this forum is so helpful I'm hoping someone can help me out. Recently my sequoia has been throwing the PO172. The vehicle has over 200k and still has the original 02 sensors (I know they should be changed due to mileage, but was waiting for 02 specific code to come up). I don't want to throw money at it but was wondering if this is the issue. The MAF has been cleaned (new air filter as well) a while back and I could clean that again.

I do have scanner and have the following info: This was taken at idle approx 700rpm with engine warmed up. Hopefully this info. can help determine if I do have an issue with the 02 or not.

02B1S1 voltage 3.263, 02B2S1 voltage 3.270, O2B1S2 voltage .680, O2B2S2 voltage .740.

Short Fuel Trim bank2 -2.3%, Long Fuel Trim bank2 -25.8%

Short Fuel Trim bank1 -.8%, Long Fuel Trim bank1 -28.1%

Also add the car runs fine. I don't detect black smoke or engine miss. If it wasn't for this code popping up, I wouldn't know anything is wrong with the vehicle.

Appreciate if someone can provide any suggestions.

Thanks

MikeM

 

[T.Tech]

If you lean out the mixture by disconnecting a vacuum line, possibly the one for the purge vsv, you should see sensor 1s be about 3.8 v or higher and sensor 2s be close to 0 if they are sensors most likely not the cause.

 

[LittleCaesar]

Sorry to revive an old thread but had to sign up again due to inactivity. I do have a 4runner, but my issue is with my Sequoia and since this forum is so helpful I'm hoping someone can help me out. Recently my sequoia has been throwing the PO172. The vehicle has over 200k and still has the original 02 sensors (I know they should be changed due to mileage, but was waiting for 02 specific code to come up). I don't want to throw money at it but was wondering if this is the issue. The MAF has been cleaned (new air filter as well) a while back and I could clean that again.

I do have scanner and have the following info: This was taken at idle approx 700rpm with engine warmed up. Hopefully this info. can help determine if I do have an issue with the 02 or not.

02B1S1 voltage 3.263, 02B2S1 voltage 3.270, O2B1S2 voltage .680, O2B2S2 voltage .740.

Short Fuel Trim bank2 -2.3%, Long Fuel Trim bank2 -25.8%

Short Fuel Trim bank1 -.8%, Long Fuel Trim bank1 -28.1%

Also add the car runs fine. I don't detect black smoke or engine miss. If it wasn't for this code popping up, I wouldn't know anything is wrong with the vehicle.

Appreciate if someone can provide any suggestions.

Thanks

MikeM

Mike,

Given your long term trim numbers are negative, it indicates that your 2UZ is running rich.

How many O2 sensors does your Sequoia have?

To rule out a vacuum leak, at least most of the time, warm up the Sequoia to operating temp, then rev the engine to around 2000 rpms and check those long term fuel trim values. If they decrease towards zero, then it usually indicates that a vacuum leak exists.

Ever clean the MAF?

 

[TucsonMike]

Thanks for the responses guys. I did notice when I rev it up to 2500rpm the long term values I believe decrease slightly but don't recall what those values were. I'll check it again tomorrow. It has 4 total. I have cleaned the MAF about a year or so ago. Will have to verify when.

I'll pull a vacuum hose off and see what happens to those readings

Thanks again

MikeM

 

[TucsonMike]

At 2000 RPM long fuel trims dropped down to -15.6 for both banks. As I raved it higher they continued to drop some. Does that indicate possible vacuum leak? MAF was cleaned less than 10k miles ago

Thanks

 

[LittleCaesar]

At 2000 RPM long fuel trims dropped down to -15.6 for both banks. As I raved it higher they continued to drop some. Does that indicate possible vacuum leak? MAF was cleaned less than 10k miles ago

Thanks

While you possibly have a vacuum leak, it isn’t large enough to trip the money light. Usually, but not always, if you have one present those long term numbers would be close to zero while reving the engine to around 2000 rpms.

When warmed up what is your MAF value at idle in g/s?

 

[Bad Luck]

Vacuum leaks 99 percent of the time cause the vehicle to run lean and your fuel trim values to be positive. I would check your spark plugs condition. Toyota oxygen sensors seem to last around 200k so I would also recommend replacing the upstream oxygen sensor. The downstream oxygen sensor is mainly used to monitor catalytic converter efficiency. Since both banks are running rich I wouldn’t suspect coolant in the cylinders or a leaky injector.

Does the 2UZ have an EGR system? A stuck open EGR valve can cause a false O2 reading.

 

[TucsonMike]

At idle MAF reads 4.53 g/s at 2500RPM 16 40g/s Appears to be the correct range from what I've read. Also new air filter less than 5000miles ago. From what I've read I dont think motor has a EGR. Could fuel pressure regulate be bad?

 

[LittleCaesar]

Those MAF numbers are right to spec, no problem there.

I don’t if you can read the fuel rail pressure for the 2uz through the ECM or a pressure gauge is needed like for the 5vz.

From here, if I were in your shoes, I would look at the voltages values and the switching of the 02 sensors in graph form, to see if there are any anomalies. Then clear the code(s) and wait for the money light to come back on. Then take a look at the Freeze Frame data, to see which of of the data values is out of spec.

Usually when I have dealt with PO 171 and 172 codes, and the car/truck seems to run OK to well, I usually suspect the oxygen sensors have become lazy. It happens with time and mileage.

 

[TucsonMike]

Thanks for the suggestions. I'll see what my scanner can do and how much of a pain it is to check fuel pressure. Since car 05 model with 220k on original 02 and fuel pump it certainly can be those. If 02 aren't too terrible to change out probably not bad idea to replace them anyway due to age and mileage. Appreciate everyone taking time to respond. I'll follow up once I get this thing fixed

 

[RoxToy00]

Hey Mike, similar problem, ever finally resolve yours? My '00 4runner 2wd v6 auto with 240k miles started running ruff when accelerating, threw P0301 code (cyl. 1 miss), replaced all 3 coil pacs, all wires, 6 plugs, 6 injectors (injector in cyl. 1 came out in two pieces, literally), and ran great for 10 min, then CEL back on, idle never dropped from 1200, throwing P0172 code (sys too rich bank 1 - which is bank 1, dr or pass?). I let it sit overnite, again drove around the block, CEL stayed on, parked and plugged in a CAN OBD2 little red scanner and pulled the following information:
DICFR2F P0172 and CEL
FUEL SYS 1 CL
FUEL SYS 2 NA
LOAD PCT 18.4

ETC 178
SHRT FT1 -20.3
LONG FT1 -19.5
RPM 795
VSS 21
IAT 86

MIL STAT OFF
MISFIRE MON OK
FUEL SYS MON OK
COMP COMPON OK
CAT MON INC
HTD CAT NA
EVAP SYS MON INC
SEC AIR SYS NA
A/C REFRIG MON NA
OXY SEN MON INC
OXY SYS HTR OK
EGR SYS NA

Then i cleared the codes, CEL went off, drove again around the block a couple time, and no CEL, and no codes, and 790 idle. I am a believer in Toyota greatness, but come on, a self-repairing car? Any ideas? And what does a flashing CEL mean? receiving codes, or what?

 

[spartacus]

flashing cel mostly means unburned fuel, misfire. Bank one is on passenger side.

 

[TucsonMike]

I haven't fixed mine but since the check engine light hasn't come on in awhile I'm going to wait until it comes on more constantly

 

[gamefreakgc]

A rich code, P0172 means unburnt fuel is getting downstream to the O2 sensor. Low compression, I mean really low, can cause this code as the fuel doesn't completely burn off, such as a cracked exhaust valve that allows the fuel just to float downstream during the compression stroke. Ever done a compression test?

 

[TucsonMike]

Follow up: Since I had over 220k on O2s I decided to replace them with new denso units. Looking at the data I could see I was getting better response but the LTFT were still high. About 100miles later code came back on. I decided to take it to dealer and see what they could find out. They disconnected the battery and cleaned the throttle body. They said throttle body was gummed up which surprised me as I thought I had cleaned it (I didnt) and by disconnecting the battery it erased memory. As of now all is fine and data looks good and worth the $150.

Thanks

MikeM

 

[Granulated_sugar]

Trying to find the solution to my p0172 - did cleaning the throtte body actually fix your CEL?

 

[TucsonMike]

Yes. So far so good but in my case it could have been a combination of old O2 sensors and gummed up throttle body. Good luck. How does the MAF look? Is it cleaned? What all have u done?