P0171 but not running lean?

[Coppertone82]

Hey all,

2002 146k mild tune from JDM otherwise stock. I have a check engine light for Bank 1 running lean, but when I checked the fuel trims on my tuner it says they’re all running normal. I cleaned the MAF as an easy start, but no luck. Any idea what this could be?
Thanks!

 

[FleeMan]

It's more than likely a vacuum leak. I would start checking the PCV hoses and the elbow that's underneath the turkey pan.

 

[Coppertone82]

It's more than likely a vacuum leak. I would start checking the PCV hoses and the elbow that's underneath the turkey pan.

Excellent, thank you for the response.

 

[Vinnie_B]

P0171 - System to Lean (Bank 1)


Check the following as a possible cause for this DTC:


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).

* View Freeze Frame Data to determine operating conditions when DTC was set. Observe LONGFT1 and 2 PID'S



Obtain Freeze Frame Data

Freeze Frame Data can be helpful in duplicating and diagnosing adaptive fuel concerns. This data (a snapshot of certain PID values, recorded at the time the DTC was stored in Continuous Memory) is helpful to determine how the vehicle was being driven when the fault occurred, and can be especially useful on intermittent concerns. Freeze Frame Data, in many cases, can help to isolate possible areas of concern as well as rule out others


Using the LONGFT1 and LONGFT2 (dual bank engines) PIDs

The LONGFT1/2 PIDs can be useful for diagnosing fuel trim concerns. A negative PID value indicates that fuel is being reduced to compensate for a rich condition, while a positive PID value indicates that fuel is being increased to compensate for a lean condition. It is important to know that there is a separate LONGFT value that is used for each rpm/load point of engine operation. When viewing the LONGFT1/2 PIDs, the values may change a great deal as the engine is operated at different rpm and load points. This is because the fuel system may have learned corrections for fuel delivery concerns that can change as a function of engine rpm and load. The LONGFT1/2 PIDs will display the fuel trim currently being used at that rpm and load point. Observing these changes in LONGFT1/2 can help when diagnosing fuel system concerns.



Lightning FastElectrical Automotive Repair LLC
PM Me or [email protected]
Website: Lightning Fast Electrical Automotive Repair LLC
Remote or Local (On Site) Technical Repair

 

[Coppertone82]

P0171 - System to Lean (Bank 1)


Check the following as a possible cause for this DTC:


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).

* View Freeze Frame Data to determine operating conditions when DTC was set. Observe LONGFT1 and 2 PID'S



Obtain Freeze Frame Data

Freeze Frame Data can be helpful in duplicating and diagnosing adaptive fuel concerns. This data (a snapshot of certain PID values, recorded at the time the DTC was stored in Continuous Memory) is helpful to determine how the vehicle was being driven when the fault occurred, and can be especially useful on intermittent concerns. Freeze Frame Data, in many cases, can help to isolate possible areas of concern as well as rule out others


Using the LONGFT1 and LONGFT2 (dual bank engines) PIDs

The LONGFT1/2 PIDs can be useful for diagnosing fuel trim concerns. A negative PID value indicates that fuel is being reduced to compensate for a rich condition, while a positive PID value indicates that fuel is being increased to compensate for a lean condition. It is important to know that there is a separate LONGFT value that is used for each rpm/load point of engine operation. When viewing the LONGFT1/2 PIDs, the values may change a great deal as the engine is operated at different rpm and load points. This is because the fuel system may have learned corrections for fuel delivery concerns that can change as a function of engine rpm and load. The LONGFT1/2 PIDs will display the fuel trim currently being used at that rpm and load point. Observing these changes in LONGFT1/2 can help when diagnosing fuel system concerns.



Lightning FastElectrical Automotive Repair LLC
PM Me or [email protected]
Website: Lightning Fast Electrical Automotive Repair LLC
Remote or Local (On Site) Technical Repair

Oh wow, a lot to unpack here haha. Thanks for the info!