System Too Lean – Bank 1

Description:

How does a P0171 code trigger the check engine light? This code will trigger the check engine light as follows:

The adaptive fuel strategy in the vehicle’s computer constantly monitors the fuel delivery system to make sure the engine is running at an optimum air to fuel ratio, which is 14.7:1. The computer adjusts injector pulse width to regulate the amount of fuel going into the engine. The oxygen sensors relay information to the Powertrain Control Module (computer), informing it of the oxygen content in the exhaust. This information is translated by the computer, and used to determine if more or less fuel is needed. The computer will then adjust fuel flow (and possibly other related engine operating characteristics), to keep the correct air fuel mixture. This loop continues as long as the engine is running. Please refer to our article Oxygen Sensor Code Diagnosis for more info on this system. A P0171 check engine light code is set when the computer has reached a rich calibration limit and can not add enough fuel to maintain the correct mixture.

Possible Causes:

Refer to our Oxygen Sensor Code Diagnosis article for a list of all possible causes. The following is an overview of P0171 check engine light code possible causes.

Fuel System:

Leaking or faulty fuel pressure regulator
Plugged or dirty fuel filter or lines
Fuel pump weak or defective check valve
Injectors leaking or faulty
Low fuel pressure or running out of fuel
Leaking EVAP system components
Faulty FRP (Fuel Rail Pressure Sensor)

Air Intake System

Vacuum leaks
Contaminated, damaged or faulty Mass Air Flow sensor
PCV valve leak or stuck open
Air induction turbulance caused by wrong filter
Oil dipstick not seated
Air leaks after the Mass Air Flow Sensor (MAF)
Oil coated aftermarket air filter

Exhaust System

Any exhaust leak before or near the oxygen sensors

EGR System

Vacuum line disconnected from EGR System Module (ESM)
EGR valve, tube or gasket leak
EGR vacuum regulator valve leaking

Secondary Air Injection System

Mechanically stuck secondary air injection valve

Mass Air Flow (MAF) Circuit Low Input

Description:

How does a P0102 code trigger the check engine light? The engine light will come on if the following concern is present:

The Mass Air Flow Sensor circuit is monitored by the powertrain control module (computer), for low voltage (which translates to low air flow) through the Comprehensive Component Monitor (CCM). With the key on and engine running, if the voltage drops below a minimum value this code will be set, causing the check engine light to illuminate.

Possible Causes:

MAF Sensor disconnected
MAF Sensor circuit open to computer
Vehicle Power circuit open to MAF Sensor
Power Ground circuit open to MAF Sensor
MAF Sensor Return circuit open to PCM
MAF Sensor circuit shorted to Ground
Intake air leak near MAF Sensor
Damaged MAF Sensor
Damaged computer

Diagnostic Help:

Refer to an appropriate manual for specification. If MAF Sensor voltage reading is below minimum limit with key on engine running then concern is a hard fault (present now). If all values are in spec proceed with intermittent diagnosis (refer to our “Intermittent Diagnosis Help” article through the “articles” link on the Navigation Bar). You may also use the “Get Help” link if you need specifications or have any other related questions.

Recent Comments
  • RESET ENGINE OIL LIFE CADILLAC CT6 ON 2014-2017
    How to reset oil life for Cadillac CT6 from years 2016, 2017 To turning off the Oil Life Light on 2016, 2017 Cadillac CT6, conform to the following instructions: Press SEL button on the steering wheel Scroll to Info Pages and press SEL button Hit the Up/Down button until you see the “OIL LIFE REMAINING” […]
  • RESET ENGINE OIL LIFE HYUNDAI VELOSTER ON 2014-2017
    How to reset oil life for Hyundai Veloster from years 2014, 2015, 2016, 2017 To turning off the Oil Life Light on 2014, 2015, 2016, 2017 Hyundai Veloster, conform to the following instructions: Turn the ignition to position On without starting the engine. Press and hold the TRIP button until you enter to “User Setting” […]
  • Reset Oil Change Warning Light for Dacia Duster 2009-2015
    How to Reset Oil Change Warning Light for Dacia Duster 2009-2015: Step-by-Step Guide Introduction If you own a Dacia Duster from 2009-2015, it’s essential to know how to reset the oil change warning light. This light serves as a reminder to change your engine oil at the required intervals, ensuring your vehicle’s optimal performance. In […]
  • Service light reset dashboard BMW X5 and BMW X6
    How do you reset maintenance light, reset service light indicator BMW X5 and BMW X6, year 2000-2013. For reset maintenance light and that can be made manually by use button on car dashboard. Reset oil service light, engine oil life BMW X5 and BMW X6, year 2000-2013 oil reset instructions: Turn the ignition to the […]
  • Service light reset dashboard BMW with 20 pin connector
    How do you reset maintenance light, reset service light BMW with 20 pin connector. For reset maintenance light and that can be made manually by use button on car dashboard. Reset service light, engine oil life BMW with 20 pin connector, oil reset instructions: How to reset oil maintenance light on BMW with 20 pin […]