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DTC P0172

DTC P0172 System too rich
DETECTION CONDITION 
  • The PCM monitors the short term fuel trim (SHRTFT) and long term fuel trim (LONGFT) when under closed loop fuel control. If the fuel trim is less than the specification, the PCM determines that the 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.
  • PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
  • FREEZE FRAME DATA (Mode 2/Mode 12) is available.
  • The DTC is stored in the PCM memory.
POSSIBLE CAUSE 
  • Erratic signal to PCM
    • APP sensor signal malfunction
    • ECT sensor signal malfunction
    • MAF sensor signal malfunction
    • TP sensor signal malfunction
    • VSS signal malfunction
  • Excess air suction in intake-air system
  • Leakage exhaust gas
  • A/F sensor looseness
  • A/F sensor malfunction
  • Fuel line pressure malfunction
    • Fuel pump unit malfunction
    • Pressure regulator (built-in fuel pump unit) malfunction
  • Purge solenoid valve malfunction
  • Fuel pump speed control malfunction
  • PCM malfunction
DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1 IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA (MODE 2) 
  • Is the DTC P0172 on FREEZE FRAME DATA (Mode 2)?
 Yes Go to the next step.
No Go to the troubleshooting procedure for DTC on FREEZE FRAME DATA (Mode 2).
(See DTC TABLE ).
2 VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED 
  • Have the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (fuel system related) been recorded?
 Yes Go to the next step.
No Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
3 VERIFY RELATED REPAIR INFORMATION AVAILABILITY 
  • Verify related Service Bulletins and/or on-line repair information availability.
  • Is any related repair information available?
 Yes Perform repair or diagnosis according to the available repair information.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
4 VERIFY RELATED PENDING CODE OR STORED DTC 
  • 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 misfire DTC is present, go to Step 8.
  • If other DTC is present, go to the appropriate DTC inspection.

    (See DTC TABLE ).
No
  • If drive ability concern is present, go to Step 8.
  • If other, go to the next step.
5 VERIFY CURRENT INPUT SIGNAL STATUS 
 Yes Go to the next step.
No Repair or replace the malfunctioning part according to the inspection results, then go to Step 11.
6 VERIFY CURRENT INPUT SIGNAL STATUS UNDER FREEZE FRAME DATA (MODE 2) CONDITION 
CAUTION:
  • While performing this step with vehicle driving, always operate the vehicle in a safe and lawful manner.
  • When the M-MDS is used to observe monitor system status while driving, be sure to have another technician with you, or record the data in the M-MDS using the PID/DATA MONITOR AND RECORD function and inspect later.

  • Access the following PIDs using the M-MDS under the FREEZE FRAME DATA (Mode 2) condition:

    (See ON-BOARD DIAGNOSTIC TEST ).

    • APP
    • ECT
    • MAF
    • TP REL
    • VSS
  • Are the PIDs normal?

    (See PCM INSPECTION ).

 Yes Go to the next step.
No Repair or replace the malfunctioning part according to the inspection results, then go to Step 11.
7 INSPECT A/F SENSOR 
 Yes Inspect for following:
  • Air suction at following due to cracks, damages and loosing parts:
    • From air cleaner to throttle body
    • From throttle body to dynamic chamber
    • From dynamic chamber and intake manifold
    • Vacuum hoses
    NOTE:
    • Engine speed may change when rust penetrating agent is sprayed on the air suction area.
  • Exhaust gas leakage between exhaust manifold and A/F sensor.
  • Loose installation of A/F sensor.

If there is no malfunction detected, replace the A/F sensor, then go to Step 11.
(See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ).
If there are malfunctions detected, repair or replace the malfunctioning part, then go to Step 11.
No Go to the next step.
8 INSPECT FUEL LINE PRESSURE 
 Yes Replace the fuel pump unit, then go to Step 11.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION ).
No Go to the next step.
9 INSPECT LONG TERM FUEL TRIM 
  • Access the LONGFT1 PID using the M-MDS.

    (See ON-BOARD DIAGNOSTIC TEST ).

  • Compare the LONGFT1 PID with recorded FREEZE FRAME DATA (Mode 12) at Step 2.
  • Is the LONGFT1 PID above FREEZE FRAME DATA (Mode 12)?
 Yes Inspect the purge solenoid valve.
(See PURGE SOLENOID VALVE INSPECTION ).
  • If there is any malfunction, replace the purge solenoid valve, then go to Step 11.
No Go to the next step.
10 INSPECT FUEL PUMP SPEED CONTROL OPERATION 
 Yes Repair or replace the malfunctioning part according to the inspection results, then go to the next step.
No Go to the next step.
11 VERIFY TROUBLESHOOTING OF DTC P0172 COMPLETED 
  • Make sure to reconnect all disconnected connectors.
  • Clear the DTC from the PCM memory using the M-MDS.

    (See AFTER REPAIR PROCEDURE ).

  • Perform the KOER self test.

    (See KOEO/KOER SELF TEST ).

  • Is the PENDING CODE same as the DTC present?
 Yes Replace the PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION ).
No Go to the next step.
12 VERIFY AFTER REPAIR PROCEDURE 
 Yes Go to the applicable DTC inspection.
(See DTC TABLE ).
No DTC troubleshooting completed.
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