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What does it mean to "fuel trim too lean" and "valve cover cracked at the oil fill neck"?

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It means vacuum leak, with valve cover crack, that will give you a lean problem, replace valve cover and clear codes.Should be good to go.

Posted on Aug 19, 2010


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What is Pc171 Code

It's P0171 & P0174 not Pc 171 & Pc174 ! The engine computer has detected a lean condition ! That mean's it's not getting enough fuel or has a vacuum leak , bad O2 sensor ! fuel pump getting weak . fuel pressure regulator weak !
P0171 - System to Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. Refer to Section 1 , Powertrain Control Software, Fuel Trim for more information. Air Measurement System
  • MAF sensor (contaminated, damaged, malfunctioning, etc.)
Fuel System
  • Fuel pressure regulator (leaking, malfunctioning, etc.).
  • Fuel filter plugged, dirty.
  • Fuel pump (weak, check valve leaking, etc.).
  • Leaking/contaminated fuel injectors.
  • Low fuel pressure or running out of fuel.
  • EVAP canister purge valve leaking (when canister is "clean").
  • Fuel supply line restricted.
  • Fuel rail pressure sensor (incorrect reading).
Air Induction System
  • Air leaks after the MAF.
  • Vacuum Leaks.
  • PCV system (leak, valve stuck open, etc.)
  • Improperly seated engine oil dipstick.
Exhaust System
  • Exhaust leaks before or near the HO2Ss (exhaust manifold gasket, mating gaskets, etc.).
EGR System
  • EGR valve tube/gasket leak
  • EVR solenoid vacuum leak
Secondary Air Injection
  • Damaged/malfunctioning secondary air injection system (mechanically stuck valve).
  • P0174 - System to Lean (Bank 2) The Adaptive Fuel Strategy continuously monitors the fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. Refer to Section 1 , Powertrain Control Software, Fuel Trim for more information. See Possible Causes for DTC P0171. See Diagnostic Aides for DTC P0171
View Freeze Frame Data to determine operating conditions when DTC was set. Observe LONGFT1 and 2 PID(s). Refer to Section 2 , Adaptive Fuel DTCs Diagnostic Techniques for more information.

Feb 12, 2015 | 2002 Ford Escape

2 Answers

Why do you get code p0171,p0174/

Code 171 means the fuel mixture is too lean on bank one and code 174 is the same thing for bank two. So I doubt the O2 sensors are faulty. Chances are you have a fuel problem, maybe low fuel pressure.

Aug 04, 2014 | 2003 Ford Explorer Sport XLT

1 Answer

I am getting po171 on my 1996 jeep

only that code???????
which engine? of the 3. (ill pretend 4 liter I-6,)
how many miles one engine, and do you service it? fully?
the fsm covers this. need that?
171 is lean AFR. lean AIR/FUEL/RATIO. (or lean fuel mix)
it means the 02 front sensor B1S1 is lean.
the fsm lists 10 causes after a new 02 , dont cure it.
first is low fuel pressure.
in geek speak (ASE) it means fuel trim show gross lean.
the OBD2 systems have trim level trip points.
if you were to scan the PCM youd see LTFT way the heck off.
and id fix that first.
the 171 means the 02 is stuck at 0v. super lean.
or is shifted lean,, only looking at it with a scope or scan tool shows
you what it is DOING.
if stuck at 0v, idling, its bad, the sensor or there is and exhaust leak
allowing outside 20% oxygen to hit this sensor and slam it horrid lean for ever.
that is why you just scan it and look. not just a useless code reader.
good scan tools you can scan and graph the 02,
and see this.
if i dont see this, i then work this full time. with a battery of tests.
there are many causes.. over 20.

see blue line in the full scan graph?
we can scan and graph 12 values at once, 1996 car too. any car.
see DSO photos(scope)

the full manual is here chapter 9 cover this 100%

me,. i try an new 02 , and with that i know it can't lie.
and then use the to find why.
weak MAF (Dirty)
intake leaks (maf engines)
exhaust cracks. hoepless this.
gross misfire sends 20% oxgen down stream, so i look for misfire like a hawk. felt , heard or see engine shake that is misfire.
low fuel pressure 58psi is good.
those are the big ones.

good luck.

btw, if a V6? or other V engine
a bad maf will cause both banks to go lean. (mines a 3.8L v6)
so.............. no engine stated, no details....

Mar 01, 2014 | 1996 Jeep Grand Cherokee

2 Answers

P0174 P0172 P0171 P0300 p0101 P0175

I had the trooper in for an oil change and emmissions check. Next day, it almost stalled. After a couple trips, it started to stall every time it stopped and I tried to start up again.

Turned out, the tubing coming out of the MAF has a hose clamp around it. That hose clamp could freely spin around. I tightened it up. The truck started running better. And after 3-4 trips, the codes cleared themselves.

Reading about it, there are a lot more causes, but this was apparently mine. IDK why it was loose. Something at the inspection place. Maybe they did it on purpose because they wanted nearly $80 to replace the fuel filter (a $10 part) and I refused.

Nov 05, 2013 | 1999 Isuzu Trooper

2 Answers

Fuel trim bank 1 permissible range exceeded

If it's only on bank1, you may have poor flow from the injectors. If you get the code for bank 2 show even as "p/d" then a possible vacuum leak. Unmetered air is telling the pre-cat O2 sensor a lean condition. The computer will add more fuel, up to 20% and then it throws the code. Suggest you do a fuel injector cleaner in-tank next fillup. If code persists have the smoke test done to check for vacuum leak. Q: How's is your idle?

Oct 25, 2013 | BMW Cars & Trucks

1 Answer

2002 suburban

Are you sure it is a trans code. Everything that I have found states that P0170 is a fuel trim problem?P0170 Fuel Trim Malfunction (Bank 1)

The code P0170 means that the air-fuel mixture coming in to the engine is too lean, or too rich. Usually it's the lean condition that causes this code. The code P0173 means the same, only for the Bank 2. Some car manufacturers list the description for the code P0170 as self adaptation out of limits.
The code P0170 could be caused by a number of reasons, such as vacuum leaks, bad PCV valve, or other parts of crankcase ventilation system, low fuel pressure, bad oxygen sensor, bad MAF sensor or even a bad EGR vlave.

Apr 05, 2012 | Chevrolet Suburban 1500 Cars & Trucks

3 Answers

My mom has a 2003 ford windstar and just last week the check engine light came on. We took it in to have it looked and it came up with the codes PO171 and PO174, what can those codes mean?

it means you may have a big vacuum leak, or the maf sensors little wires inside of it are dirty and need to be cleaned, or the maf sensor failed. Also there is a TSB that says to remove the PCV valve on the valve cover near the radiator, Then remove the little rubber grommet and look inside. At about the 5 oclock position you may see a little hole on the plate that is above the valves . If you see the hole then your suppose to replace the valve cover.
If all this fails to fix the problem then you need to remove the intake plennun and inspect and replace the gaskets.

Jan 12, 2010 | 2003 Ford Windstar

1 Answer

99 CHEVY trouble shoot code P0171

LEAN TROUBLE CODES (P0171 or P0174) A code P0171 or P0174 indicate the engine is running lean. This means there is too much air and/or not enough fuel. You can confirm the engine is running lean by looking at Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Normally, STFT and LTFT should be plus or minus 8 from zero. If STFT and/or LTFT are more than about +10 or higher, it indicates the engine is running LEAN. Negative numbers (-10 or more) indicates the engine is running RICH. A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

______________________________-- Causes A code P0171 may mean that one or more of the following has happened:
  • The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
  • There could be a vacuum leak downstream of the MAF sensor.
Possible Solutions Possible solutions include:
  • In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
  • Inspect all vacuum and PCV hoses, replace if necessary
  • Check for a dirty fuel filter and proper fuel pressure

Jan 02, 2010 | 2001 Dodge Ram 1500 Truck 2WD

1 Answer

I neeed the part that the oil filler cap attaches to. What is it called?

You mean the oil filler neck that attaches to the valve cover? Are you talking about a filler neck?

Jul 28, 2009 | 2000 Jeep Grand Cherokee

1 Answer

Code p1131 on a 1999 mercury cougar

Lack of HO2S-11 Switch, Indicates Lean.Right bank front 02 sensor. When an HO2S sensor indicates lean at the end of a test, the system is trying to correct for an over-lean condition. The code is set when the fuel control system no longer detects switching for a calibrated amount of time.In other words the 02 sensor is indicating lean and the fuel trim has reached the programed limit trying to correct it.
There are many things that could cause this like a bad 02 sensor,a vacuum leak,a leaking or contaminated fuel injector/s,a stuck open PCV valve,leak in hose between MAF sensor and engine causing un-metered or unmeasured air entering the engine,exhaust leak,improperly seated oil dipstick,stuck EGR valve.
Check PCV valve first if it is stuck open if you pull the hose off of the valve cover that hooks to the air tube between MAF and engine you will feel a strong vacuum pull there,normal you would hardly feel it.

Mar 11, 2009 | 1999 Mercury Cougar

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