Need help - DTC P0171, P0174 Chk Engine Light, VSC off, VSC TRAC - Toyota Tundra Forums : Tundra Solutions Forum
 
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post #1 of 3 (permalink) Old 03-26-2019, 06:14 PM Thread Starter
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Need help - DTC P0171, P0174 Chk Engine Light, VSC off, VSC TRAC

Hi all,
I'm extremely happy with my '07 Sequoia, bought it in 2009 and have put about 180,000 miles on it since and it has been nothing but reliable. Just rolled over 200,000 as well.
The check engine, VSC TRAC, and VSC OFF lights are all illuminated.
Everything about the vehicle's drivability is normal, no power loss or hesitation during normal driving and WOT. The real issue is that my gas mileage has gone from ~14mpg down to 8-9mpg per the trip computer in the headliner. Really hurting the wallet and I'm only getting about 200 miles per tank.
I've tried most of the simple things, like cleaning the MAF sensor, and visually inspecting the vacuum lines and other parts of the intake, but I'm not sure what to do next besides throwing parts at it.
To further diagnose the issue, I purchased a mini vci cable to go with Toyota's techstream software so I can pull the codes and access other sensor data.

I pulled these codes from the ECU and VSC computer:
P0171 - System Too Lean (Bank 1)
P0174 - System Too Lean (Bank 2)
C1201 - Engine Control System Malfunction

My understanding is that the VSC computer is not happy with the lean codes, and therefore disabling the VSC system?
I've also look at the fuel trims and O2 sensor data at idle, various engine speeds and during driving and I'm not exactly sure how to interpret all the data.

Data @ idle:
Engine Speed: 694 rpm
MAF: 4.12 gm/sec
Intake Air: 127 F
Short FT B1S1: 0.0%
Short FT B2S1: 0.7%
Long FT B1S1: 36.7%
Long FT B2S1: 44.5%

Data @ ~3000rpm:
Engine Speed: 3071 rpm
MAF: 20.56 gm/sec
Intake Air: 126 F
Short FT B1S1: -2.4%
Short FT B2S1: -2.4%
Long FT B1S1: 29.6%
Long FT B2S1: 32.8%

Again, not exactly sure how to read this data. Bank 2 seems a bit off, but what I'm confused about is that the STFT stays +-5% from 0 when I rev the engine, but the LT trim's are so skewed.
I read online that the LTFT's going down on RPM increase would suggest a vacuum leak, and LTFT's going up on rpm increase would suggest issues with the fuel system, so would it be safe to assume that this is a vacuum or exhaust leak?
I also should note that when stopped and idling in my driveway, occasionally I can faintly smell exhaust gases from inside the cabin with the A/C on and all doors/windows closed. Leaking exhaust manifolds seem to be common with these Sequoias, however I don't hear the infamous ticking noise or any other obvious signs of an exhaust leak.

I know this thread is a bit of a mess, so if you need something cleared up or any more data please let me know. Any help or pointers would be appreciated!
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post #2 of 3 (permalink) Old 03-26-2019, 07:19 PM
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Re: Need help - DTC P0171, P0174 Chk Engine Light, VSC off, VSC TRAC

Do a search on this site just by typing in the codes you have. Read through some of these and see if they help you narrow it down.


https://www.tundrasolutions.com/foru...6-p0174-p0171/


https://www.tundrasolutions.com/foru...l-p0171-p0174/

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post #3 of 3 (permalink) Old 04-13-2019, 03:12 AM
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Re: Need help - DTC P0171, P0174 Chk Engine Light, VSC off, VSC TRAC

I would surely search there. . . .
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