#
DTC P0171

id010200818400

## Without WU-TWC

DTC P0171 | Fuel trim system too lean
--- | ---
DETECTION CONDITION | • The PCM monitors the short term fuel trim (SHRTFT) and the long term fuel trim (LONGFT) values during the closed loop fuel control. If the fuel trim exceeds the preprogrammed criteria, the PCM determines that the fuel system is too lean. Diagnostic support note • This is a continuous monitor. (FUEL SYSTEM) • The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. • The PENDING CODE is available if the PCM detects the above malfunction conditions during first drive cycle. • The FREEZE FRAME DATA is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE | • Misfire • HO2S deterioration • HO2S heater malfunction • Pressure regulator malfunction • Fuel pump malfunction • Fuel filter clogged or restricted • Fuel leakage on the fuel line from the fuel delivery pipe and fuel pump • Fuel return hose clogged • Leakage in the exhaust system • The Purge solenoid valve malfunction • The Purge solenoid hoses are improperly connected • Insufficient compression • The Variable valve timing control system is improperly connected operation

Diagnostic procedure

STEP | INSPECTION | ACTION
--- | --- | ---
1 | PERFORM DTC CONFIRMATION PROCEDURE • Perform the DTC CONFIRMATION PROCEDURE. (See DTC CONFIRMATION PROCEDURE.) • Is the same DTC present? | Yes | Go to the next step.
No | Intermittent concern exists. Go to the INTERMITTENT CONCERN TROUBLESHOOTING procedure. (See INTERMITTENT CONCERN TROUBLESHOOTING.)
2 | VERIFY RELATED PENDING CODE OR STORED DTCS • Turn the ignition switch off, then to the ON position (Engine off). • Verify the related PENDING CODE or stored DTCs. • Are other DTCs present? | Yes | If a misfire DTC is present, go to step 7. If an other DTC is present, go to the appropriate DTC troubleshooting procedures. (See DTC TABLE.)
No | If a driveability concern is present, go to Step 7. If not, go to the next step.
3 | IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0171 displayed in FREEZE FRAME DATA? | Yes | Go to the next step.
No | Go to the troubleshooting procedures for the DTC on the FREEZE FRAME DATA.
4 | VERIFY CURRENT INPUT SIGNAL STATUS (IGNITION SWITCH TO ON/IDLE) • Access the ECT, MAF, TP, and VSS PIDs using the WDS or equivalent. (See PCM INSPECTION [WITHOUT WU-TWC], PCM INSPECTION [WITH WU-TWC].) • Is there any signal that is way off the specification when the ignition switch is in the ON position and the engine is running? | Yes | Inspect the suspected sensor and excessive resistance in related wiring harnesses. Repair or replace if necessary. Then go to Step 17.
No | Go to the next step.
5 | VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION • Inspect the same PIDs as Step 4 while simulating the FREEZE FRAME DATA condition. • Is there any input signal which causes drastic changes? | Yes | Inspect the suspected sensor and related wiring harnesses, and repair or replace it. Then go to Step 17.
No | Go to the next step.
6 | VERIFY CURRENT INPUT SIGNAL STATUS OF HO2S • Access the O2S11 for P0171 PID using WDS or equivalent. • Check the PID under the following accelerator pedal conditions (in PARK (ATX) or NEUTRAL (MTX)). • Is the PID reading normal? - 0.55 V or more when the accelerator pedal is suddenly depressed (rich condition). - 0.55 V or less just after releasing of accelerator pedal (lean condition) | Yes | Inspect for air suction at the following due to cracks, damage or loose parts: • From the air cleaner to throttle body • From the throttle body to dynamic chamber • From the dynamic chamber to the intake manifold • Vacuum hoses Note • Engine speed may change if a rust penetrating agent is sprayed on the air suction area. Repair or replace any the malfunctioning part, then go to Step 17.
No | Visually inspect for any gas leakage between the exhaust manifold and HO2S. • If there is no leakage, replace the HO2S. Then go to Step 17.
7 | INSPECT MAF PID • Start the engine. • Access the MAF PID using the WDS or equivalent. • Verify that the MAF PID changes quickly according to the RPM when racing the engine. • Is the MAF PID response normal? | Yes | Go to the next step.
No | Replace mass air flow sensor, then go to Step 17.
8 | INSPECT FOR EXCESSIVE AIR SUCTION OF INTAKE AIR SYSTEM • Visually inspect for loose, cracked or damaged hoses in the intake air system. • Is there any malfunction? | Yes | Repair or the replace source of the air suction, then go to Step 17.
No | Go to the next step.
9 | INSPECT FUEL LINE PRESSURE • Turn the ignition switch off. Note • If the engine won't start, inspect the fuel line pressure with the ignition switch in the ON position. • Inspect the fuel line pressure while the engine is running. (See FUEL LINE PRESSURE INSPECTION.) • Is fuel line pressure normal? | Yes | Go to step 13.
No | • If the fuel line pressure is too high: Go to the next step, then go to Step 17. • If the fuel line pressure is too low: Go to next step 11.
10 | VERIFY VACUUM IS LEADING TO PRESSURE REGULATOR • Disconnect the vacuum hose from the pressure regulator. • Verify that a vacuum is felt at the open port of the disconnected vacuum hose. • Is a vacuum felt? | Yes | Inspect the fuel pump maximum pressure and the fuel return hose. • If any problem is found, repair or replace the if necessary part. • If all the above items are normal, replace the pressure regulator. Then go to Step 17.
No | Verify that the vacuum hoses are connected correctly. • If normal, go to the next step. • If not normal, reconnect the vacuum hoses, then go to Step 17.
11 | INSPECT FUEL PUMP MAXIMUM PRESSURE • Perform a fuel pump maximum pressure test. • Is the fuel pump maximum pressure within 500-850 kpa {5.1-8.6 kgf/cm 2, 73-120 psi}? | Yes | Go to step.
No | Inspect the fuel pump circuit for an open or poor connections. Repair or replace the suspected circuit, then go to Step 17. If the circuit is normal, replace the fuel pump, then go to Step 17.
12 | INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE • Visually inspect the fuel line for any leakage. • Is any fuel leakage found? | Yes | Replace the suspected fuel line, then go to Step 17.
No | Inspect fuel filters for the following: • Restriction or clogging at the fuel filter (high-pressure). • Foreign material or staining inside the fuel filter (low-pressure) Perform the following actions. • If restriction or clogging is found at the fuel filter (high-pressure), replace the fuel filter (high-pressure). • If foreign material or staining are found inside the fuel filter (low-pressure), clean out the fuel tank and the filter. • If all items above are normal, replace the pressure regulator. Then go to Step 17.
13 | INSPECT IGNITION SYSTEM • Carry a out spark test. • Is a strong blue spark visible at each cylinder? | Yes | Go to the next step.
No | Repair or replace the malfunctioning parts according to the the spark test results. Then go to Step 17.
14 | INSPECT ENGINE COMPRESSION • Inspect the engine compression. (See COMPRESSION INSPECTION [ZJ, ZY].) • Is it normal? | Yes | Go to the next step.
No | Implement the engine overhaul for repairs, then go to Step 17.
15 | INSPECT VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION • Inspect the variable valve timing control system operation. (See Variable Valve Timing Control System Operation Inspection, Variable Valve Timing Control System Operation Inspection.) • Does the variable valve timing control system work properly? | Yes | Go to the next step.
No | Repair or replace the malfunctioning parts according to variable valve timing control system inspection results, then go to Step 17.
16 | INSPECT FUEL INJECTOR OPERATION • Remove the fuel injector. • Inspect injector operation. • Is the fuel injector normal? | Yes | Go to the next step.
No | Replace the fuel injector, then go to the next step.
17 | VERIFY TROUBLESHOOTING OF DTC P0171 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from the PCM memory using the WDS or equivalent. • Perform the KOER self-test. (See KOEO/KOER SELF-TEST.) • Is the same DTC present? | Yes | Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION.)
No | Go to the next step.
18 | VERIFY AFTER REPAIR PROCEDURE • Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE.) • Are any DTCs present? | Yes | Go to the applicable DTC troubleshooting. (See DTC TABLE.)
No | Troubleshooting completed.

## With WU-TWC

DTC P0171 | Fuel trim system too lean
--- | ---
DETECTION CONDITION | • The PCM monitors the short term fuel trim (SHRTFT) and the long term fuel trim (LONGFT) values during the closed loop fuel control. If the LONGFT and the sum total of these fuel trims exceeds the preprogrammed criteria, the PCM determines that the fuel system is too lean. Diagnostic support note • This is a continuous monitor. (FUEL SYSTEM) • The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. • The PENDING CODE is available if PCM detects the above malfunction conditions during the first drive cycle. • The FREEZE FRAME DATA is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE | • Misfire • HO2S deterioration • HO2S heater malfunction • MAF sensor malfunction • Pressure regulator (built-in fuel pump unit) malfunction • Fuel pump malfunction • Fuel filter clogged or restricted • Fuel leakage on the fuel line from the fuel delivery pipe and fuel pump • Leakage in the exhaust system • Purge solenoid valve improper operation • Purge solenoid valve malfunction (stuck open) • The purge solenoid hoses are improperly connected • Air suction in intake-air system • Insufficient engine compression • The variable valve timing control system operation is improper • PCM malfunction

Diagnostic procedure

STEP | INSPECTION | ACTION
--- | --- | ---
1 | PERFORM DTC CONFIRMATION PROCEDURE • Perform the DTC CONFIRMATION PROCEDURE. • Is the same DTC present? | Yes | Go to the next step.
No | Intermittent concern exists. Go to the INTERMITTENT CONCERN TROUBLESHOOTING procedure.
2 | VERIFY RELATED PENDING CODE OR STORED DTCS • Turn the ignition switch off, then to the ON position (Engine off). • Verify the related PENDING CODE or stored DTCs. • Are other DTCs present? | Yes | If a misfire DTC is present, go to step 7. If any other DTC is present, go to the appropriate DTC troubleshooting procedures.
No | If a driveability concern is present, go to Step 7. If not, go to the next step.
3 | IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0171 displayed in FREEZE FRAME DATA? | Yes | Go to the next step.
No | Go to the troubleshooting procedures for the DTC on the FREEZE FRAME DATA.
4 | VERIFY CURRENT INPUT SIGNAL STATUS (IGNITION SWITCH TO ON/IDLE) • Access the ECT, MAF, TP, and VSS PIDs using the WDS or equivalent. • Is there any signal that is way off the specification when the ignition switch is in the ON position and the engine is running? | Yes | Inspect the suspected sensor and excessive resistance in related wiring harnesses. Repair or replace if necessary. Then go to Step 17.
No | Go to the next step.
5 | VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION • Inspect the same PIDs as Step 4 while simulating the FREEZE FRAME DATA condition. • Is there any input signal which causes drastic changes? | Yes | Inspect the suspected sensor and related wiring harnesses, and repair or replace it. Then go to Step 17.
No | Go to the next step.
6 | VERIFY CURRENT INPUT SIGNAL STATUS OF HO2S • Access the O2S11 for P0171 PID using the WDS or equivalent. • Check the PID under the following accelerator pedal conditions (in PARK (ATX) or NEUTRAL (MTX)). • Is the PID reading normal? - 0.45 V or more when the accelerator pedal is suddenly depressed (rich condition). - 0.45 V or less just after releasing accelerator pedal (lean condition) | Yes | Inspect for air suction at the following due to cracks, damage or loose parts: • From the air cleaner to the throttle body • From the throttle body to the dynamic chamber • From the dynamic chamber to the intake manifold • Vacuum hoses Note • Engine speed may change if a rust penetrating agent is sprayed on the air suction area. Repair or replace any the malfunctioning part, then go to Step 17.
No | Visually inspect for any gas leakage between the exhaust manifold and HO2S. • If there is no leakage, replace the HO2S. Then go to Step 17.
7 | INSPECT MAF PID • Start the engine. • Access the MAF PID using the WDS or equivalent. • Verify that MAF PID changes quickly according to the RPM when racing the engine. • Is the MAF PID response normal? | Yes | Go to the next step.
No | Replace the mass air flow sensor, then go to Step 17.
8 | INSPECT FOR EXCESSIVE AIR SUCTION OF INTAKE AIR SYSTEM • Visually inspect for loose, cracked or damaged hoses in the intake air system. • Is there any malfunction? | Yes | Repair or replace the source of the air suction, then go to Step 17.
No | Go to the next step.
9 | INSPECT FUEL LINE PRESSURE • Turn the ignition switch off. Note • If the engine won't start, inspect the fuel line pressure with the ignition switch in the ON position. • Inspect the fuel line pressure while the engine is running. • Is fuel line pressure normal? | Yes | Go to step 13.
No | • If the fuel line pressure is too high: Go to the next step, then go to Step 17. • If the fuel line pressure is too low: Go to next Step 11.
10 | VERIFY VACUUM IS LEADING TO PRESSURE REGULATOR • Disconnect the vacuum hose from the pressure regulator. • Verify that a vacuum is felt at the open port of the disconnected vacuum hose. • Is a vacuum felt? | Yes | Inspect the fuel pump maximum pressure and the fuel return hose. • If any problem is found, repair or replace parts if necessary. • If all the above items are normal, replace the pressure regulator. Then go to Step 17.
No | Verify that the vacuum hoses are connected correctly. • If normal, go to the next step. • If not normal, reconnect the vacuum hoses, then go to Step 17.
11 | INSPECT FUEL PUMP MAXMUM PRESSURE • Perform the fuel pump maximum pressure test. • Is the fuel pump maximum pressure within 500-850 kpa {5.1-8.6 kgf/cm 2, 73-120 psi}? | Yes | Go to step.
No | Inspect the fuel pump circuit for an open circuit or poor connections. Repair or replace the suspected circuit, then go to Step 17. If the circuit is normal, replace the fuel pump, then go to Step 17.
12 | INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE • Visually inspect the fuel line for any leakage. • Is any fuel leakage found? | Yes | Replace the suspected fuel line, then go to Step 17.
No | Inspect the fuel filters for the following: • Restriction or clogging at the fuel filter (high-pressure). • Foreign material or staining inside the fuel filter (low-pressure) Perform the following actions. • If restriction or clogging is found at the fuel filter (high-pressure), replace the fuel filter (high-pressure). • If foreign materials or staining are found inside the fuel filter (low-pressure), clean out the fuel tank and the filter. • If all items above are normal, replace the pressure regulator. Then go to Step 17.
13 | INSPECT IGNITION SYSTEM • Carry a out spark test. • Is a strong blue spark visible at each cylinder? | Yes | Go to the next step.
No | Repair or replace the malfunctioning parts according to the spark test results. Then go to Step 17.
14 | INSPECT ENGINE COMPRESSION • Inspect the engine compression. • Is it normal? | Yes | Go to the next step.
No | Implement the engine overhaul for repairs, then go to Step 17.
15 | INSPECT VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION • Inspect the variable valve timing control system operation. • Does the variable valve timing control system work properly? | Yes | Go to the next step.
No | Repair or replace the malfunctioning parts according to the variable valve timing control system inspection results, then go to Step 17.
16 | INSPECT FUEL INJECTOR OPERATION • Remove the fuel injector. • Inspect injector operation. • Is the fuel injector normal? | Yes | Go to the next step.
No | Replace the fuel injector, then go to the next step.
17 | VERIFY TROUBLESHOOTING OF DTC P0171 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from the PCM memory using the WDS or equivalent. • Perform the "PCM Adaptive Memory Procedure Drive Mode". • Is the PENDING CODE for this DTC present? | Yes | Replace the PCM, then go to the next step.
No | Go to the next step.
18 | VERIFY AFTER REPAIR PROCEDURE • Perform the "AFTER REPAIR PROCEDURE". • Are any DTCs present? | Yes | Go to applicable DTC troubleshooting.
No | Troubleshooting completed.