P0172
DTC P0172: System too RichSystem too Rich Circuit
- Refer to, DTC P0201 - P0204 Injector Circuit Malfunction.
CIRCUIT OPERATION
- Refer to, DTC P0201 - P0204 Injector Circuit Malfunction.
TECHNICAL DESCRIPTION
- If a malfunction occurs in the fuel system, the fuel trim value becomes too small.
- The ECM
DESCRIPTIONS OF MONITOR METHODS
- If an excessively rich state of air-fuel ratio is detected from the learned air-fuel ratio (long-term fuel trim) and the feedback air-fuel ratio (short-term fuel trim), a malfunction is determined to have occurred.
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)
- Volume airflow sensor
- Barometric pressure sensor
- Intake air temperature sensor
- Engine coolant temperature sensor
- Throttle position sensor
DTC SET CONDITIONS
Logic Flow Chart:
Logic Flowchart
Check Conditions
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 77 °C (171 °F).
- Volume airflow sensor output frequency is 81 Hz or more.
Judgment Criteria
- Long-term fuel trim has continued to be lower than -12.5 percent for 5 seconds.
or
- Short-term fuel trim has continued to be lower than -6.0 percent for 5 seconds.
Check Conditions
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 77 °C (171 °F).
- Volume airflow sensor output frequency is 81 Hz or less.
Judgment Criteria
- Long-term fuel trim has continued to be lower than -12.5 percent for 5 seconds.
or
- Short-term fuel trim has continued to be lower than -11.0 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is higher than 77 °C (171 °F).
- Under the closed loop air/fuel ratio control.
Judgment Criteria
- Long-term fuel trim has continued to be -12.5 percent for 5 seconds.
or
- Short-term fuel trim has continued to be -25.0 percent for 5 seconds.
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 2 - Fuel Trim Monitor. OBD-II Drive Cycle Pattern Lists
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Volume airflow sensor failed.
- Injector failed.
- Incorrect fuel pressure.
- Heated oxygen sensor failed.
- Engine coolant temperature sensor failed.
- Intake air temperature sensor failed.
- Barometric pressure sensor failed.
- Exhaust leak.
- Use of incorrect or contaminated fuel.
- ECM failed.
- PCM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
STEP 1. Using scan tool MB991958, check data list item 12: Volume Airflow Sensor.
CAUTION: To 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 12, Volume Airflow Sensor.
4. Warm up the engine to normal operating temperature: 80 °C to 96 °C (176 °F to 205 °F).
- When idling, between 20 and 46 Hz (between 1.3 and 3.3 gm/s).
- When 2,500 r/min, between 70 and 110 Hz (between 6.6 and 10.2 gm/s).
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 2.
NO: Refer to, DTC P0101 - Volume Airflow Circuit Range/Performance Problem, DTC P0102 - Volume Airflow Circuit Low Input.
STEP 2. Using scan tool MB991958, check data list item 13: 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 13, 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.
Q: Is the sensor operating properly?
YES: Go to Step 3.
NO: 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 21: 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 21, 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.
Q: Is the sensor operating properly?
YES: Go to Step 4.
NO: 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 25: Barometric Pressure Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991958 to the data reading mode for item 25, Barometric 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. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 5.
NO: Refer to, DTC P2227 - Barometric Pressure Circuit Range/Performance Problem, DTC P2228 - Barometric Pressure Circuit Low Input, DTC P2229 - Barometric Pressure Circuit High Input.
STEP 5. Check the injector.
1. Disconnect each injector connector.
2. Measure the resistance between injector side connector terminal No. 1 and No. 2.
Standard value: 13 - 16 ohms [at 20 °C (68 °F)]
Q: Is the resistance between 13 and 16 ohms [at 20 °C (68 °F)]?
YES: Go to Step 6.
NO: Replace the injector. Then go to Step 8.
STEP 6. Check the fuel pressure.
Refer to On-vehicle Service - Fuel Pressure Test.
Q: Is the fuel pressure normal?
YES: Go to Step 7.
NO: Repair or replace 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 - Procedure 2 - Fuel Trim Monitor.
3. Check the diagnostic trouble code (DTC).
Q: Is DTC P0172 set?
YES: Replace the ECM or PCM. Then go to Step 8.
NO: The procedure 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 - Procedure 2 - Fuel Trim Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0172 set?
YES: Retry the troubleshooting.
NO: The inspection is complete.