DTC P0171 [LF, L3]


DTC P0171	Fuel trim system too lean
DETECTION CONDITION	• The PCM monitors short term fuel trim (SHRTFT) and long term fuel trim (LONGFT) values during 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 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 • Front HO2S deterioration • Front 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 • Purge solenoid valve malfunction • The purge solenoid hoses are improperly connected • Insufficient compression • The variable valve timing control system operation (L3 engine) is improper


STEP	INSPECTION		ACTION
1	PERFORM DTC CONFIRMATION PROCEDURE • Perform the DTC CONFIRMATION PROCEDURE. (See DTC CONFIRMATION PROCEDURE [LF, L3].) • Is the same DTC present?	Yes	Go to the next step.
1		No	Intermittent concern exists. Go to the INTERMITTENT CONCERN TROUBLESHOOTING procedure. (See INTERMITTENT CONCERN TROUBLESHOOTING [LF, L3].)
2	VERIFY RELATED PENDING CODE OR STORED DTCS • Turn the ignition switch to the OFF, then ON (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. (See DTC TABLE [LF, L3].)
2		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 the FREEZE FRAME DATA?	Yes	Go to the next step.
3		No	Go to the troubleshooting procedures for the DTC in FREEZE FRAME DATA.
4	VERIFY CURRENT INPUT SIGNAL STATUS (IGNITION KEY TO ON/IDLE) • Access the ECT, MAF, TP, and VSS PIDs using the WDS or equivalent. (See PCM INSPECTION [LF, L3].) • Is there any signal that is far out of specification when the ignition switch is in the ON position and the engine is running?	Yes	Inspect the suspected sensor for excessive resistance in the related wiring harnesses. Repair or replace if necessary. then go to Step 18.
4		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 18.
5		No	Go to the next step.
6	VERIFY CURRENT INPUT SIGNAL STATUS OF FRONT HO2S • Access the O2S11 for the 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? - Above 0.55 V when the accelerator pedal is suddenly depressed (rich condition). - Below 0.55 V just after accelerator pedal is released (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 malfunctioning part, then go to Step 18.
6		No	Visually inspect for any gas leakage between the exhaust manifold and front HO2S. • If there is no leakage, replace the FRONT HO2S. then go to Step 18.
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.
7		No	Replace the mass air flow sensor, then go to Step 18.
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 18.
8		No	Go to the next step.
9	INSPECT FUEL LINE PRESSURE • Turn the ignition switch to the OFF. Note • If the engine won't start, inspect the fuel line pressure with ignition switch to the ON. • Inspect the fuel line pressure while the engine is running. (See FUEL LINE PRESSURE INSPECTION [LF, L3].) • Is the fuel line pressure normal?	Yes	Go to step 11.
9		No	• If the fuel line pressure is too high: Replace fuel pump unit, then go to Step 18. • If the fuel line pressure is too low: Go to the next step.
10	INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE • Visually inspect fuel line for any leakage. • Is any fuel leakage found?	Yes	Replace the suspected fuel line, then go to Step 18.
10		No	Inspect the fuel filters for the following: • Restriction or clogging at fuel filter (high-pressure side). • Foreign materials or stain inside fuel filter (low-pressure side) Perform following actions as result. • If restriction or clogging is found at fuel filter (high-pressure side), replace fuel pump unit. • If foreign materials or stain is found inside the fuel filter (low-pressure side), clean the fuel tank and filter. • If all the above items are normal, replace the fuel pump unit. then go to Step 18.
11	CHECK IGNITION COIL OPERATION AND HIGH-TENSION LEAD WITH TIMING LIGHT • Verify blinking condition on each cylinder using the timing light at idle. • Do all the cylinders show a blinking condition?	Yes	Go to Step 15.
11		No	Go to the next step.
12	CHECK HIGH-TENSION LEADS FOR NO BLINKING CYLINDER • Turn the ignition switch to the OFF position. • Inspect high-tension leads for installation condition, corrosion on terminal, open lead and damaged cover. • Is the condition of high-tension lead normal?	Yes	Go to the next step.
12		No	Replace the malfunctioning high-tension lead, then go to Step 18.
13	INSPECT POWER SUPPLY TERMINAL AT IGNITION COIL CONNECTOR • Disconnect the ignition coil connector. • Turn the ignition switch to the ON position (Engine off). • Check the voltage at the ignition coil connector terminal B (harness-side) and body ground. • Is the voltage B+?	Yes	Go to the next step.
13		No	Check for an open circuit between the ignition coil connector and the ignition switch. Repair or replace the wiring harness, then go to Step 18.
14	INSPECT IGNITION COIL RESISTANCE • Check the ignition coil resistance. (See IGNITION COIL INSPECTION [LF, L3].) • Is the coil resistance normal?	Yes	Go to the next step.
14		No	Replace the ignition coil, then go to Step 18.
15	INSPECT ENGINE COMPRESSION • Inspect the engine compression. (See COMPRESSION INSPECTION [LF, L3].) • Is it normal?	Yes	Go to the next step.
15		No	Implement the engine overhaul for repairs, then go to Step 18.
16	INSPECT VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION Note • The following test should be performed for the variable valve timing control system. Go to the next step for vehicles without the variable valve timing control system. • Inspect the variable valve timing control system operation. (See Variable Valve Timing Control System Operation Inspection (L3 Engine Models).) • Does the variable valve timing control system work properly?	Yes	Go to the next step.
16		No	Repair or replace the malfunctioning part according to variable valve timing control system inspection results, then go to Step 18.
17	INSPECT FUEL INJECTOR OPERATION • Remove the fuel injector. • Inspect the injector operation. • Is the fuel injector normal?	Yes	Go to the next step.
17		No	Replace the injector, then go to the next step.
18	VERIFY TROUBLESHOOTING OF DTC P0171 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from PCM memory using the WDS or equivalent. • Perform the KOER self-test. (See KOEO/KOER SELF-TEST [LF, L3].) • Is the same DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [LF, L3].)
18		No	Go to the next step.
19	VERIFY AFTER REPAIR PROCEDURE • Perform the "After Repair Procedure". (See AFTER REPAIR PROCEDURE [LF, L3].) • Are any DTCs present?	Yes	Go to the applicable DTC troubleshooting. (See DTC TABLE [LF, L3].)
19		No	Troubleshooting completed.