DTC P0171 [L3]


DTC P0171	Fuel trim system too lean
DETECTION CONDITION	• PCM monitors short term fuel trim (SHRTFT) and long term fuel trim (LONGFT) values during OBD DRIVE MODE operation. If fuel trim exceeds preprogrammed criteria, PCM determines that the fuel system is too lean. Diagnostic support note • This is a continuous monitor. (FUEL SYSTEM) • MIL illuminates if 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. • PENDING CODE is available if PCM detects the above malfunction conditions during first drive cycle. • FREEZE FRAME DATA is available. • 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 in fuel line from fuel delivery pipe and fuel pump • Fuel return hose clogged • Leakage exhaust system • Purge solenoid valve malfunction • Purge solenoid hoses improper connection • Insufficient compression


STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA HAS BEEN RECORDED • Has FREEZE FRAME DATA been recorded?	Yes	Go to next step.
1		No	Record FREEZE FRAME DATA on repair order, then go to next step.
2	VERIFY RELATED SERVICE INFORMATION AVAILABILITY • Check for related Service Information availability. • Is any related Service Information available?	Yes	Perform repair or diagnosis according to available Service Information. • If vehicle is not repaired, go to next step.
2		No	Go to next step.
3	VERIFY RELATED PENDING CODE OR STORED DTCS • Turn ignition key to OFF, then ON (Engine OFF). • Verify related PENDING CODE or stored DTCs. • Is any other DTC present?	Yes	If misfire DTC is present, go to step 8. If other DTC is present, go to appropriate DTC troubleshooting procedures. (See DTC TABLE [L3].)
3		No	If drive ability concern is present, go to Step 8. If not, go to next step.
4	IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0171 on FREEZE FRAME DATA?	Yes	Go to next step.
4		No	Go to troubleshooting procedures for DTC on FREEZE FRAME DATA.
5	VERIFY CURRENT INPUT SIGNAL STATUS (IGNITION KEY TO ON/IDLE) • Access ECT, MAF, TP and VSS PIDs using WDS or equivalent. (See PCM INSPECTION [L3].) • Is there any signal that is far out of specification when ignition key is at ON and engine is running?	Yes	Inspect suspected sensor and excessive resistance in related wiring harnesses. Repair or replace if necessary. Then go to Step 18.
5		No	Go to next step.
6	VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION • Inspect same PIDs as Step 5 while simulating FREEZE FRAME DATA condition. • Is there any input signal which causes drastic changes?	Yes	Inspect suspected sensor and related wiring harnesses, and repair or replace it. Then go to Step 18.
6		No	Go to next step.
7	VERIFY CURRENT INPUT SIGNAL STATUS OF FRONT HO2S • Access O2S11 PID using WDS or equivalent. • Inspect PID under following accelerator pedal condition (in NEUTRAL). - Above 0.55 V when accelerator pedal is suddenly depressed (rich condition). - Below 0.55 V just after release of accelerator pedal (lean condition) • Is PID reading okay?	Yes	Inspect for air suction in following due to cracks, damage and loose parts: • From air cleaner to throttle body • From throttle body to dynamic chamber • From dynamic chamber to intake manifold • Vacuum hoses Note • Engine speed may change when rust penetrating agent is sprayed on the air suction area. Repair or replace any faulty part, then go to Step 18.
7		No	Visually inspect for any gas leakage between exhaust manifold and front HO2S. • If there is no leakage, replace front HO2S. Then go to Step 18.
8	INSPECT MAF PID • Start engine. • Access MAF PID using WDS or equivalent. • Verify that MAF PID changes quickly according to engine RPM while racing engine. • Is MAF PID response okay?	Yes	Go to next step.
8		No	Replace Mass air flow sensor, then go to Step 18.
9	INSPECT FOR EXCESSIVE AIR SUCTION OF INTAKE-AIR SYSTEM • Visually inspect for loose, cracked or damaged hoses in intake-air system. • Is there any malfunction?	Yes	Repair or replace source of air suction, then go to Step 18.
9		No	Go to next step.
10	INSPECT FUEL LINE PRESSURE • Turn ignition key to OFF. Note • If engine won't start, inspect fuel line pressure with ignition key at ON. • Inspect fuel line pressure while engine running. (See FUEL LINE PRESSURE INSPECTION [L3].) • Is fuel line pressure okay?	Yes	Go to step 12.
10		No	• If fuel line pressure is too high: Replace fuel pump unit, then go to Step 18. • If fuel line pressure is too low: Go to next step.
11	INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE • Visually inspect fuel line for any leakage. • Is any fuel leakage found?	Yes	Replace suspected fuel line, then go to Step 18.
11		No	Inspect fuel filters for following: • Restriction or clogging in fuel filter (high-pressure side). • Foreign materials or clogging in fuel filter (low-pressure side) Perform following actions depending on the result above. • If restriction or clogging is found in fuel filter (high-pressure side), replace fuel pump unit. • If foreign materials or clogging is found in fuel filter (low-pressure side), clean out fuel tank and filter (low-pressure side). • If all items above are okay, replace fuel pump unit. Then go to Step 18.
12	CHECK IGNITION COIL OPERATION AND HIGH-TENSION LEAD WITH TIMING LIGHT • Verify blinking condition for each cylinder using timing light at idle. • Do all cylinders show blinking condition?	Yes	Go to Step 16.
12		No	Go to next step.
13	CHECK HIGH-TENSION LEADS OF NON- BLINKING CYLINDER • Turn ignition key to OFF. • Inspect high-tension leads for installation condition, corrosion on terminal, open lead and damaged cover. • Is condition of high-tension lead okay?	Yes	Go to next step.
13		No	Replace faulty high-tension lead, then go to Step 18.
14	INSPECT POWER SUPPLY TERMINAL AT IGNITION COIL CONNECTOR • Disconnect ignition coil connector. • Turn ignition key to ON (Engine OFF). • Check voltage at ignition coil connector terminal B (harness-side) and body ground. • Is voltage B+?	Yes	Go to next step.
14		No	Inspect for open circuit between ignition coil connector and ignition switch. Repair or replace wiring harness, then go to Step 18.
15	INSPECT IGNITION COIL RESISTANCE • Inspect ignition coil resistance. (See IGNITION COIL INSPECTION [L3].) • Is coil resistance okay?	Yes	Go to next step.
15		No	Replace ignition coil, then go to Step 18.
16	INSPECT ENGINE COMPRESSION • Inspect engine compression. (See COMPRESSION INSPECTION [L3].) • Is compression okay?	Yes	Go to next step.
16		No	Implement engine overhaul for repairs, then go to Step 18.
17	INSPECT FUEL INJECTOR OPERATION • Remove fuel injector. • Inspect injector operation. (SeeFUEL INJECTOR INSPECTION [L3].) • Is fuel injector okay?	Yes	Go to next step.
17		No	Replace injector, then go to next step.
18	VERIFY TROUBLESHOOTING OF DTC P0171 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear DTC from PCM memory using WDS or equivalent. • Run OBD DRIVE MODE. (See OBD DRIVE MODE [L3].) • Is PENDING CODE of same DTC present?	Yes	Replace PCM, then go to next step. (See PCM REMOVAL/INSTALLATION [L3].)
18		No	Go to next step.
19	VERIFY AFTER REPAIR PROCEDURE • Perform "After Repair Procedure". (See AFTER REPAIR PROCEDURE [L3].) • Is there any DTC present?	Yes	Go to applicable DTC troubleshooting. (See DTC TABLE [L3].)
19		No	Troubleshooting completed.