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DTC P0172: System too Rich
 
 
 
 
Fuel Trim Circuit
  • Refer to, DTC P0261 - Injector Circuit Low input - Cylinder 1 , DTC P0264 - Injector Circuit Low Input - Cylinder 2 , DTC P0267 - Injector Circuit Low Input - Cylinder 3 , DTC P0270 - Injector Circuit Low Input - Cylinder 4 .
 
 
CIRCUIT OPERATION
  • Refer to, DTC P0261 - Injector Circuit Low input - Cylinder 1 , DTC P0264 - Injector Circuit Low Input - Cylinder 2 , DTC P0267 - Injector Circuit Low Input - Cylinder 3 , DTC P0270 - Injector Circuit Low Input - Cylinder 4 .
 
 
TECHNICAL DESCRIPTION
  • If a malfunction occurs in the fuel system, the fuel trim value becomes too large.
  • The ECM checks whether the fuel trim value is within a specified range.
 
 
DESCRIPTIONS OF MONITOR METHODS
  • Air/fuel learning value (long time fuel trim) and air/fuel feedback integral value (short time fuel trim) are too rich.
 
 
MONITOR EXECUTION
  • Continuous
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
  • Misfire monitor
Sensor (The sensor below is determined to be normal)
  • Mass airflow sensor
  • Engine coolant temperature sensor
  • Intake air temperature sensor
  • Barometric pressure sensor
  • Throttle position sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C (169°F).
  • Mass airflow sensor output is more than 9 g/sec.
Judgment Criterion
  • Long-term fuel trim is less than -12.5 percent for 5 seconds.
or
  • Short-term fuel trim is less than -10.2 percent for 5 seconds.
Check Conditions
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C (169°F).
  • Mass airflow sensor output is less than 9 g/sec.
Judgment Criterion
  • Long-term fuel trim is less than -12.5 percent for 5 seconds.
or
  • Short-term fuel trim is less than -15.2 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is more than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
Judgment Criterion
  • Long-term fuel trim is -12.5 percent for 2 seconds.
or
  • Short-term fuel trim is -25.0 percent for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 21 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Mass airflow sensor failed.
  • Injector failed.
  • Incorrect fuel pressure.
  • Engine coolant temperature sensor failed.
  • Intake air temperature sensor failed.
  • Barometric pressure sensor failed.
  • Manifold absolute pressure sensor failed.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tool:
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: V.C.I.
    • MB991827: USB Cable
    • MB991910: Main Harness A
STEP 1. Using scan tool MB991958, check data list item 10: Mass Airflow Sensor.
cautionTo prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958 to the data link connector.
(2) Start the engine and run at idle.
(3) Set scan tool MB991958 to the data reading mode for item 10, Mass Airflow Sensor.
(4) Warm up the engine to normal operating temperature: 80°C to 95°C (176°F to 203°F).
  • When idling, between 1,350 and 1,670 millivolts.
  • When 2,500 r/min, between 1,620 and 2,020 millivolts.
(5) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 2.
Refer to, DTC P0102 - Mass Airflow Circuit Low Input , DTC P0103 - Mass Airflow Circuit High Input .
 
STEP 2. Using scan tool MB991958, check data list item 5: Intake Air Temperature Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool MB991958 to the data reading mode for item 5, Intake Air Temperature Sensor.
  • The intake air temperature and temperature shown with the scan tool should approximately match.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 3.
Refer to, DTC P0111 - Intake Air Temperature Circuit Range/Performance Problem , DTC P0112 - Intake Air Temperature Circuit Low Input , DTC P0113 - Intake Air Temperature Circuit High Input .
 
STEP 3. Using scan tool MB991958, check data list item 6: Engine Coolant Temperature Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool MB991958 to the data reading mode for item 6, Engine Coolant Temperature Sensor.
  • The engine coolant temperature and temperature shown with the scan tool should approximately match.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 4.
Refer to, DTC P0116 - Engine Coolant Temperature Circuit Range/Performance Problem , DTC P0117 - Engine Coolant Temperature Circuit Low Input , DTC P0118 - Engine Coolant Temperature Circuit High Input .
 
STEP 4. Using scan tool MB991958, check data list item 8: Manifold Absolute Pressure Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool MB991958 to the data reading mode for item 8, Manifold Absolute Pressure Sensor.
  • When altitude is 0 m (0 foot), 101 kPa (29.8 in.Hg).
  • When altitude is 600 m (1,969 feet), 95 kPa (28.1 in.Hg).
  • When altitude is 1,200 m (3,937 feet), 88 kPa (26.0 in.Hg).
  • When altitude is 1,800 m (5,906 feet), 81 kPa (23.9 in.Hg).
(3) Start the engine.
  • Warm up the engine. When the engine is idling, 16 - 36 kPa (4.7 - 10.6 in.Hg).
  • When the engine is suddenly revved, manifold absolute pressure varies.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 5.
Refer to, DTC P0106 - Manifold Absolute Pressure Circuit Range/Performance Problem , DTC P0107 - Manifold Absolute Pressure Circuit Low Input , DTC P0108 - Manifold Absolute Pressure Circuit High Input .
 
STEP 5. Check the injector.
(1) Disconnect the injector connectors B-101, B-102, B-105 and B-106.
(2) Measure the resistance between each injector side connector terminal No. 1 and No. 2.
Standard value: 10.5 - 13.5 Ω [at 20°C (68°F)]
Is the measured resistance between 10.5 and 13.5 Ω [at 20°C (68°F)]?
Go to Step 6.
Replace the faulty injector. Then go to Step 8.
 
STEP 6. Check the fuel pressure.
Refer to, Fuel Pressure Test .
Is the fuel pressure normal?
Go to Step 7.
Repair it. Then go to Step 8.
 
STEP 7. Replace the injector.
(1) Replace the injector.
(2) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 21 .
(3) Check the diagnostic trouble code (DTC).
Is DTC P0172 set?
Replace the ECM (Refer to, Removal and Installation ). Then go to Step 8.
The inspection is complete.
 
STEP 8. Test the OBD-II drive cycle.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 21 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0172 set?
Retry the troubleshooting.
The inspection is complete.