lean code PO174
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Mountain Pass
Joined: Jul 2019
Posts: 135
Likes: 2
lean code PO174
Po174 lean on drivers side. There seems to be a small leak on the throttle body on DS, confirmed with spraying some carb cleaner. Pulled one of the driver spark plug it was carboned up pretty bad. I dropped it off at the shop, they said with code it's probably a throttle body leak, since the truck runs well, and it's old then to just wait, until it starts to misfire. Any thoughts?
01 f150 4.2 220,000 miles
01 f150 4.2 220,000 miles
Fleet Mechanic
Joined: Jul 2019
Posts: 1,304
Likes: 310
I’m not sure a TB leak only applies to one cylinder bank.
That carboned plug…well, these 4.2s burn oil once they get up in miles.
You ever do the intake manifold gasket and isolator bolts? At this mileage, I’d probably just ride it into the ground unless you love the truck and it’s a keeper for life. Then, I’d debate a remanned engine or younger year or mileage swap.
That carboned plug…well, these 4.2s burn oil once they get up in miles.
You ever do the intake manifold gasket and isolator bolts? At this mileage, I’d probably just ride it into the ground unless you love the truck and it’s a keeper for life. Then, I’d debate a remanned engine or younger year or mileage swap.
Fleet Mechanic
Joined: Jun 2023
Posts: 1,352
Likes: 374
From: WA
Many gasket based leaks happen only when the engine is cold. A good shop will look at freeze frame data and fuel trims.
"Wait for a misfire" means they just don't want to work on your old truck. You need to look at fuel trims to know how close you are to that point. Get a cheap OBD port tool and a free phone app and look for yourself.
https://veepeak.com/products/obdcheck-ble
https://play.google.com/store/apps/d...hl=en_US&pli=1
"Wait for a misfire" means they just don't want to work on your old truck. You need to look at fuel trims to know how close you are to that point. Get a cheap OBD port tool and a free phone app and look for yourself.
https://veepeak.com/products/obdcheck-ble
https://play.google.com/store/apps/d...hl=en_US&pli=1
Cargo Master
Joined: Oct 2011
Posts: 2,862
Likes: 765
From: SoCal/Wyoming
Just had this on mine four days ago. P0174, system too lean bank 2. I pulled the MAF sensor and cleaned it, installed a new air filter, checked for any vacuum leaks and that was it. Cleared the code and four days later, all is still good.
Hotshot
Joined: Jul 2020
Posts: 10,270
Likes: 2,566
From: Near Salt Lake City
Not sure the 01's have the same isolator bolts but I sure would pull the upper plenum off and replace the gaskets and bolts if available
Last 4.2 I had with a perpetual lean condition had failing injectors
I replaced all 6 with some China knockoff Motorcraft injectors 6 for 54 bucks or some unGODly cheap price
5 worked, took me a while to figure the 6th one was intermittently inop
Put one of the old ones that worked back in, lean solved, passed I/M ran great for years until I sold it when I got another lemon truck basically given to me again
Last 4.2 I had with a perpetual lean condition had failing injectors
I replaced all 6 with some China knockoff Motorcraft injectors 6 for 54 bucks or some unGODly cheap price
5 worked, took me a while to figure the 6th one was intermittently inop
Put one of the old ones that worked back in, lean solved, passed I/M ran great for years until I sold it when I got another lemon truck basically given to me again
Hotshot
Joined: Jul 2020
Posts: 10,270
Likes: 2,566
From: Near Salt Lake City
You need to be able to check the fuel trims and watch the front O2 sensors switch.
Can you do that with your scan tool in live data?
Can you do that with your scan tool in live data?
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Fleet Mechanic
Joined: Jun 2023
Posts: 1,352
Likes: 374
From: WA
I was just pointing out that with the lean codes sometimes what looks like a fix is not actually a long-term fix.
The internet says "dirty MAF sensor" for lean codes across all brands. But a person really needs to know what they're working with. You could fix a code in the spring and it will stay gone until the fall. When it gets cold. Freeze frame tells you conditions when the codes set. That's why the engineers created freeze frame.
The internet says "dirty MAF sensor" for lean codes across all brands. But a person really needs to know what they're working with. You could fix a code in the spring and it will stay gone until the fall. When it gets cold. Freeze frame tells you conditions when the codes set. That's why the engineers created freeze frame.
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Thread Starter
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Mountain Pass
Joined: Jul 2019
Posts: 135
Likes: 2
Many gasket based leaks happen only when the engine is cold. A good shop will look at freeze frame data and fuel trims.
"Wait for a misfire" means they just don't want to work on your old truck. You need to look at fuel trims to know how close you are to that point. Get a cheap OBD port tool and a free phone app and look for yourself.
https://veepeak.com/products/obdcheck-ble
https://play.google.com/store/apps/d...hl=en_US&pli=1
"Wait for a misfire" means they just don't want to work on your old truck. You need to look at fuel trims to know how close you are to that point. Get a cheap OBD port tool and a free phone app and look for yourself.
https://veepeak.com/products/obdcheck-ble
https://play.google.com/store/apps/d...hl=en_US&pli=1
Long term fuel trim #1 -7.6
Short term fuel trim #2 -6.
What's a good range?
Thanks
Thread Starter
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Mountain Pass
Joined: Jul 2019
Posts: 135
Likes: 2
Redid test, could not post a pic, sorry. ---------------------------------------FREEZE DATA
engine temp.189 ---------------------------------------------------------------------165
Short Term fuel trim bank one -18 to -7 ------------------------------------------Neg.1.6
LT bank one 9.4----------------------------------------------------------------------- 7.8
st fuel trim bank 2 -14 to -3---------------------------------------------------------- 0
long term bank 2 28.1 ---------------------------------------------------------------10.2
rpm 860 --------------------------------------------------------------------------------1278
load 8.2 --------------------------------------------------------------------------------45.5
engine temp.189 ---------------------------------------------------------------------165
Short Term fuel trim bank one -18 to -7 ------------------------------------------Neg.1.6
LT bank one 9.4----------------------------------------------------------------------- 7.8
st fuel trim bank 2 -14 to -3---------------------------------------------------------- 0
long term bank 2 28.1 ---------------------------------------------------------------10.2
rpm 860 --------------------------------------------------------------------------------1278
load 8.2 --------------------------------------------------------------------------------45.5
Last edited by Michael Lizotte; Feb 11, 2026 at 06:52 PM.
Fleet Mechanic
Joined: Jun 2023
Posts: 1,352
Likes: 374
From: WA
Sorry, but I can't tell what you're trying to show there. Are the numbers to the right the freeze frame data numbers? The numbers under the word FREEZE? They don't show lean, P0174, values. Fuel trims look okay.
Fleet Mechanic
Joined: Jun 2023
Posts: 1,352
Likes: 374
From: WA
Long term bank 2 is high and would probably set the lean code. Any chance you got your columns backward, or just the bank 2 numbers?
You'll probably get a better feel for how things work if you keep messing with it. I "tested" my system by starting the engine cold, and watching fuel trims as I sprayed just a very small amount of carb cleaner on the side of the intake manifold. As the liquid ran down and got sucked in the fuel trims dropped. Then they went back up again. That told me that the intake manifold gasket was leaking.
But my freeze frame numbers showed a cold engine and high positive fuel trims. Plus my engine only had 75,000 easy miles on it and ran great once it warmed up. I can't tell what your freeze frame numbers are showing. Might be worthwhile to get Forscan working smoothly so you can watch live data.
You'll probably get a better feel for how things work if you keep messing with it. I "tested" my system by starting the engine cold, and watching fuel trims as I sprayed just a very small amount of carb cleaner on the side of the intake manifold. As the liquid ran down and got sucked in the fuel trims dropped. Then they went back up again. That told me that the intake manifold gasket was leaking.
But my freeze frame numbers showed a cold engine and high positive fuel trims. Plus my engine only had 75,000 easy miles on it and ran great once it warmed up. I can't tell what your freeze frame numbers are showing. Might be worthwhile to get Forscan working smoothly so you can watch live data.