DTC P0172


DTC P0172	Fuel trim system too rich
DETECTION CONDITION	• The PCM monitors the short fuel trim (SHRTFT) and long 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 rich. 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 condition 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 • 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.) • 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.)
2	VERIFY RELATED PENDING CODE OR STORED DTCS • Turn the ignition switch off, then to the ON position (Engine off). • Verify related pending code or stored DTCs. • Is other DTCs present?	Yes	Go to the applicable DTC troubleshooting procedures.
2		No	If a driveability concern is present, go to Step 9. If not, go to the next step.
3	IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0172 display in the FREEZE FRAME DATA?	Yes	Go to the next step.
3		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 ECT, MAF, TP and VSS PIDs using the WDS or equivalent. • 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 suspected sensor and excessive resistance in related wiring harnesses. Repair or replace if necessary. Then go to Step 11.
4		No	Go to the next step.
5	VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION • Inspect PID data while simulating 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.Then go to Step 11.
5		No	Go to the next step.
6	VERIFY CURRENT INPUT SIGNAL STATUS OF HO2S • Access the O2S11 PID using the WDS or equivalent. • Verify the PID while racing engine (in PARK (ATX) or NEUTRAL (MTX)). • Is the PID reading normal? - 0.55 V or more when accelerator pedal is suddenly depressed (rich condition). - 0.55 V or less just after release of the accelerator pedal (lean condition)	Yes	Go to the next step.
6		No	Replace the HO2S. Then go to Step 11.
7	INSPECT FUEL LINE PRESSURE • Turn the ignition switch off. • Inspect fuel line pressure while the engine is running. (See FUEL LINE PRESSURE INSPECTION.) • Is fuel line pressure normal?	Yes	Go to Step 9.
7		No	Go to the next step.
8	VERIFY VACUUM IS LEADING TO PRESSURE REGULATOR • Disconnect the vacuum hose from the pressure regulator. • Verify that a vacuum is felt at the opening port of the disconnected vacuum hose. • Is a vacuum felt?	Yes	Inspect the fuel pump maximum pressure and fuel return hose. • If any problem is found, repair or replace the parts if necessary. • If all of the above items are normal, replace the pressure regulator. Then go to Step 11.
8		No	Verify that the vacuum hoses are connected correctly. • If normal, go to the next step. • If not, reconnect the vacuum hoses, then go to Step 11.
9	INSPECT IF PURGE SOLENOID VALVE IS STUCK OPEN • Turn the ignition switch off. • 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 11.
9		No	Go to the next step.
10	INSPECT PCV VALVE OPERATION • Inspect PCV valve operation. (See PCV VALVE INSPECTION.) • Is the PCV valve normal?	Yes	Go to the next step.
10		No	Replace the PCV valve, then go to the next step.
11	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 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.)
11		No	Go to the next step.
12	VERIFY AFTER REPAIR PROCEDURE • Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE.) • Are any DTCs present?	Yes	Go to applicable DTC troubleshooting. (See DTC TABLE.)
12		No	Troubleshooting completed.

With WU-TWC


DTC P0172	Fuel trim system too rich
DETECTION CONDITION	• The PCM monitors the short fuel trim (SHRTFT) and long 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 rich. 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 condition 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 fuel line from fuel delivery pipe and fuel pump • Leakage 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 • Variable valve timing control system improper operation • PCM malfunction


STEP	INSPECTION		ACTION
1	PERFORM DTC CONFIRMATION PROCEDURE • Perform the DTC CONFIRMATION PROCEDURE. • Is the same DTC present?	Yes	Go to the next step.
1		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 related pending code or stored DTCs. • Is other DTCs present?	Yes	Go to the applicable DTC troubleshooting procedures.
2		No	If a driveability concern is present, go to Step 9. If not, go to the next step.
3	IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0172 display in the FREEZE FRAME DATA?	Yes	Go to the next step.
3		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 ECT, MAF, TP and VSS PIDs using the WDS or equivalent. • 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 and excessive resistance in the related wiring harnesses. Repair or replace if necessary. Then go to Step 11.
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 11.
5		No	Go to the next step.
6	VERIFY CURRENT INPUT SIGNAL STATUS OF HO2S • Access the O2S11 PID using the WDS or equivalent. • Verify the PID while racing engine (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 release of the accelerator pedal (lean condition)	Yes	Go to the next step.
6		No	Replace the HO2S. Then go to Step 11.
7	INSPECT FUEL LINE PRESSURE • Turn the ignition switch off. • Inspect fuel line pressure while the engine is running. • Is fuel line pressure normal?	Yes	Go to Step 9.
7		No	Go to the next step.
8	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 fuel return hose. • If any problem is found, repair or replace parts if necessary. • If all of the above items are normal, replace the pressure regulator. Then go to Step 11.
8		No	Verify that the vacuum hoses are connected correctly. • If normal, go to the next step. • If not, reconnect the vacuum hoses, then go to Step 11.
9	INSPECT IF PURGE SOLENOID VALVE IS STUCK OPEN • Turn the ignition switch off. • 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 11.
9		No	Go to the next step.
10	INSPECT PCV VALVE OPERATION • Inspect the PCV valve operation. • Is the PCV valve normal?	Yes	Go to the next step.
10		No	Replace the PCV valve, then go to the next step.
11	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 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.
11		No	Go to the next step.
12	VERIFY AFTER REPAIR PROCEDURE • Perform the "AFTER REPAIR PROCEDURE". • Are any DTCs present?	Yes	Go to applicable DTC troubleshooting.
12		No	Troubleshooting completed.

DTC P0172

Without WU-TWC

With WU-TWC