DTC P0172 [LF, L3]


DTC P0172	Fuel trim system too rich
DETECTION CONDITION	• The PCM monitors short fuel trim (SHRTFT) and long 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 rich. Diagnostic support note • This is a continuous monitor. (FUEL SYSTEM) • The 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. • The PENDING CODE is available if PCM detects the above malfunction condition 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 return hose is clogged • Purge solenoid valve malfunction • the purge solenoid hoses are improperly connected • PCV valve malfunction


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 position, then ON (Engine off). • Verify related pending code or stored DTCs. • Are other DTCs present?	Yes	Go to the applicable DTC troubleshooting procedures.
2		No	If a drive ability concern is present, go to Step 8. If not, go to the next step.
3	IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0172 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. • Is there any signal that is far out of specification when ignition switch to the ON 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 10.
4		No	Go to the next step.
5	VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION • Inspect the PID data while simulating the FREEZE FRAME DATA conditions. • Is there any input signal which causes drastic changes?	Yes	Inspect the suspected sensor and related wiring harnesses, and repair or replace. then go to Step 10.
5		No	Go to the next step.
6	VERIFY CURRENT INPUT SIGNAL STATUS OF FRONT HO2S • Access the O2S11 PID using the WDS or equivalent. • Verify the PID while racing the engine (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 the accelerator pedal is released (lean condition)	Yes	Go to the next step.
6		No	Replace the front HO2S. then go to Step 10.
7	INSPECT FUEL LINE PRESSURE • Turn the ignition switch to the OFF position. • 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 the next step.
7		No	Replace fuel pump unit, then go to Step 10.
8	INSPECT PURGE SOLENOID VALVE FOR STUCKING (OPEN) • Turn the ignition switch to the OFF position. • Disconnect both hoses from the purge solenoid valve. • Blow air through the purge solenoid valve. • Can air be blown through the valve?	Yes	Replace the purge solenoid valve. then go to Step 10.
8		No	Go to the next step.
9	INSPECT PCV VALVE OPERATION • Inspect the PCV valve operation. (See PCV VALVE INSPECTION [LF, L3].) • Is the PCV valve normal?	Yes	Go to the next step.
9		No	Replace the PCV valve, then go to the next step.
10	VERIFY TROUBLESHOOTING OF DTC P0172 COMPLETED • Make sure to reconnect all disconnected connectors. • Turn the ignition switch to the ON position (Engine off). • Clear the DTC from the memory using the WDS or equivalent. • Perform 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].)
10		No	Go to the next step.
11	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].)
11		No	Troubleshooting completed.