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.
P0801 Reverse Inhibit Control Circuit
P0803 1-4 Upshift (Skip Shift) Solenoid Control Circuit
P0804 1-4 Upshift (Skip Shift) Lamp Control Circuit
P0805 Clutch Position Sensor Circuit
P0806 Clutch Position Sensor Circuit Range/Performance
P0807 Clutch Position Sensor Circuit Low
P0808 Clutch Position Sensor Circuit High
P0809 Clutch Position Sensor Circuit Intermittent
P0810 Clutch Position Control Error
P0811 Excessive Clutch Slippage
P0812 Reverse Input Circuit
P0813 Reverse Output Circuit
P0814 Transmission Range Display Circuit
P0815 Upshift Switch Circuit
P0816 Downshift Switch Circuit
P0817 Starter Disable Circuit
P0818 Driveline Disconnect Switch Input Circuit
P0820 Gear Lever X-Y Position Sensor Circuit
P0821 Gear Lever X Position Circuit
P0822 Gear Lever Y Position Circuit
P0823 Gear Lever X Position Circuit Intermittent
P0824 Gear Lever Y Position Circuit Intermittent
P0825 Gear Lever Push-Pull Switch (Shift Anticipate)
P0830 Clutch Pedal Switch “A” Circuit
P0831 Clutch Pedal Switch “A” Circuit Low
P0832 Clutch Pedal Switch “A” Circuit High
P0833 Clutch Pedal Switch “B” Circuit
P0834 Clutch Pedal Switch “B” Circuit Low
P0835 Clutch Pedal Switch “B” Circuit High
P0836 Four Wheel Drive (4WD) Switch Circuit
P0837 Four Wheel Drive (4WD) Switch Circuit Range/Performance
P0838 Four Wheel Drive (4WD) Switch Circuit Low
P0839 Four Wheel Drive (4WD) Switch Circuit High
P0840 Transmission Fluid Pressure Sensor/Switch “A” Circuit
P0841 Transmission Fluid Pressure Sensor/Switch “A” Circuit Range/Performance
P0842 Transmission Fluid Pressure Sensor/Switch “A” Circuit Low
P0843 Transmission Fluid Pressure Sensor/Switch “A” Circuit High
P0844 Transmission Fluid Pressure Sensor/Switch “A” Circuit Intermittent
P0845 Transmission Fluid Pressure Sensor/Switch “B” Circuit
P0846 Transmission Fluid Pressure Sensor/Switch “B” Circuit Range/Performance
P0847 Transmission Fluid Pressure Sensor/Switch “B” Circuit Low
P0848 Transmission Fluid Pressure Sensor/Switch “B” Circuit High
P0849 Transmission Fluid Pressure Sensor/Switch “B” Circuit Intermittent
P0600 Serial Communication Link
P0601 Internal Control Module Memory Check Sum Error
P0602 Control Module Programming Error
P0603 Internal Control Module Keep Alive Memory (KAM) Error
P0604 Internal Control Module Random Access Memory (RAM) Error
P0605 Internal Control Module Read Only Memory (ROM) Error
P0606 ECM/PCM Processor
P0607 Control Module Performance
P0608 Control Module VSS Output “A”
P0609 Control Module VSS Output “B”
P0610 Control Module Vehicle Options Error
P0615 Starter Relay Circuit
P0616 Starter Relay Circuit Low
P0617 Starter Relay Circuit High
P0618 Alternative Fuel Control Module KAM Error
P0619 Alternative Fuel Control Module RAM/ROM Error
P0620 Generator Control Circuit
P0621 Generator Lamp “L” Terminal Control Circuit
P0622 Generator Field “F” Terminal Control Circuit
P0623 Generator Lamp Control Circuit
P0624 Fuel Cap Lamp Control Circuit
P0630 VIN Not Programmed or Mismatch – ECM/PCM
P0631 VIN Not Programmed or Mismatch – TCM
P0635 Power Steering Control Circuit
P0836 Power Steering Control Circuit Low
P0637 Power Steering Control Circuit High
P0638 Throttle Actuator Control Range/Performance (Bank 1)
P0639 Throttle Actuator Control Range/Performance (Bank 2)
P0640 Intake Air Heater Control Circuit
P0645 A/C Clutch Relay Control Circuit
P0646 A/C Clutch Relay Control Circuit Low
P0647 A/C Clutch Relay Control Circuit High
P0648 Immobilizer Lamp Control Circuit (“Immobilizer” pending SAE J1930 approval)
P0649 Speed Control Lamp Control Circuit
P0650 Malfunction Indicator Lamp (ML) Control Circuit
P0654 Engine RPM Output Circuit
P0655 Engine Hot Lamp Output Control Circuit
P0656 Fuel Level Output Circuit
P0660 Intake Manifold Tuning Valve Control Circuit (Bank 1)
P0661 Intake Manifold Tuning Valve Control Circuit Low (Bank 1)
P0662 Intake Manifold Tuning Valve Control Circuit High (Bank 1)
P0663 Intake Manifold Tuning Valve Control Circuit (Bank 2)
P0664 Intake Manifold Tuning Valve Control Circuit Low (Bank 2)
P0665 Intake Manifold Tuning Valve Control Circuit High (Bank 2)
P0500 Vehicle Speed Sensor
P0501 Vehicle Speed Sensor Range/Performance
P0502 Vehicle Speed Sensor Circuit Low Input
P0503 Vehicle Speed Sensor Intermittent/Erratic/High
P0505 Idle Control System
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected
P0508 Idle Control System Circuit Low
P0509 Idle Control System Circuit High
P0510 Closed Throttle Position Switch
P0512 Starter Request Circuit
P0513 Incorrect Irnmobilizer Key (“Immobilizer pending SAE J1930 approval)
P0515 Battery Temperature Sensor Circuit
P0516 Battery Temperature Sensor Circuit Low
P0517 Battery Temperature Sensor Circuit High
P0520 Engine Oil Pressure Sensor/Switch Circuit
P0521 Engine Oil Pressure Sensor/Switch Range/Performance
P0522 Engine Oil Pressure Sensor/Switch Low Voltage
P0523 Engine Oil Pressure Sensor/Switch High Voltage
P0524 Engine Oil Pressure Too Low
P0530 A/C Refrigerant Pressure Sensor Circuit
P0531 A/C Refrigerant Pressure Sensor Circuit Range/Performance
P0532 A/C Refrigerant Pressure Sensor Circuit Low Input
P0533 A/C Refrigerant Pressure Sensor Circuit High Input
P0534 Air Conditioner Refrigerant Charge Loss
P0540 Intake Air Heater Circuit
P0541 Intake Air Heater Circuit Low
P0542 Intake Air Heater Circuit High
P0544 Exhaust Gas Temperature Sensor Circuit (Bank 1)
P0545 Exhaust Gas Temperature Sensor Circuit Low (Bank 1)
P0546 Exhaust Gas Temperature Sensor Circuit High (Bank 1)
P0547 Exhaust Gas Temperature Sensor Circuit (Bank 2)
P0548 Exhaust Gas Temperature Sensor Circuit Low (Bank 2)
P0549 Exhaust Gas Temperature Sensor Circuit High (Bank 2)
P0550 Power Steering Pressure Sensor Circuit
P0551 Power Steering Pressure Sensor Circuit Range/Performance
P0552 Power Steering Pressure Sensor Circuit Low Input
P0553 Power Steering Pressure Sensor Circuit High Input
P0554 Power Steering Pressure Sensor Circuit Intermittent
P0560 System Voltage
P0561 System Voltage Unstable
P0562 System Voltage Low
P0563 System Voltage High
P0564 Cruise Control Multi-Function Input Signal
P0565 Cruise Control On Signal
P0566 Cruise Control Off Signal
P0567 Cruise Control Resume Signal
P0568 Cruise Control Set Signal
P0569 Cruise Control Coast Signal
P0570 Cruise Control Accel Signal
P0571 Cruise Control/Brake Switch A Circuit
P0572 Cruise Control/Brake Switch A Circuit Low
P0573 Cruise Control/Brake Switch A Circuit High
P0574 Cruise Control System – Vehicle Speed Too High
P0575 Cruise Control Input Circuit
P0576 Cruise Control Input Circuit Low
P0577 Cruise Control input Circuit High
P0578 through P0580 Reserved for Cruise Control Codes
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