P0171
DTC P0171: System too LeanSystem too Lean 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 large.
- The ECM checks whether the fuel trim value is within a specified range.
DESCRIPTIONS OF MONITOR METHODS
- Air/fuel learning value (long term fuel trim) and air/fuel feedback integral value (short term fuel trim) are too lean.
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
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor
- Throttle position sensor
DTC SET CONDITIONS
Logic Flow Chart:
Logic Flow Chart
Check Conditions
- Engine coolant temperature is lower than approximately 100 degrees C (212 degrees F) when the engine is started.
- Intake air temperature is lower than 60 degrees C (140 degrees F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Volume airflow sensor output frequency is 56 Hz or more.
Judgment Criteria
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds
or
- Short-term fuel trim has continued to be higher than +10.0 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is lower than approximately 100 degrees C (212 degrees F) when the engine is started.
- Intake air temperature is lower than 60 degrees C (140 degrees F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Volume airflow sensor output frequency is 56 Hz or less.
Judgment Criteria
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
or
- Short-term fuel trim has continued to be higher than +15 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is higher than approximately 100 degrees C (212 degrees F) when the engine is started.
- Intake air temperature is higher than 60 degrees C (140 degrees F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Volume airflow sensor output frequency is 56 Hz or more.
Judgment Criteria
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
or
- Short-term fuel trim has continued to be higher than +20.0 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is higher than approximately 100 degrees C (212 degrees F) when the engine is started.
- Intake air temperature is higher than 60 degrees C (140 degrees F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Volume airflow sensor output frequency is 56 Hz or less.
Judgment Criteria
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
or
- Short-term fuel trim has continued to be higher than +25.0 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Under the closed loop air/fuel ratio control.
Judgment Criteria
- Long-term fuel trim has continued to be +12.5 percent for 2 seconds.
or
- Short-term fuel trim has continued to be +25.0 percent for 2 seconds.
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 20. 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.
- Air drawn in from gaps in gasket, seals, etc.
- Heated oxygen sensor failed.
- Engine coolant temperature sensor failed.
- Intake air temperature sensor failed.
- Barometric pressure sensor failed.
- Use of incorrect or contaminated fuel.
- ECM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
STEP 1. Check for exhaust leaks.
Q: Are there any abnormalities?
YES: Go to Step 2.
NO: Repair it. Then go to Step 14.
STEP 2. Check for intake system vacuum leaks.
Q: Are there any abnormalities?
YES: Go to Step 3.
NO: Repair it. Then go to Step 14.
STEP 3. 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 degrees C to 95 degrees C (176 degrees F to 203 degrees F).
- When idling, between 17 and 43 Hz (between 2 and 7 gm/s).
- When 2,500 r/min, between 40 and 100 Hz (between 5 and 16 gm/s).
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 4.
NO: Refer to, DTC P0101 - Volume Airflow Circuit Range/Performance Problem , DTC P0102 - Volume Airflow Circuit Low Input.
STEP 4. 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 5.
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 5. 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 6.
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 6. 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 7.
NO: Refer to, DTC P2228 - Barometric Pressure Circuit Low Input, DTC P2229 - Barometric Pressure Circuit High Input.
STEP 7. Check harness connectors B-17, B-18, B-20, B-22 at injector for damage.
Q: Is the harness connector in good condition?
YES: Go to Step 8.
NO: Repair or replace it. Then go to Step 14.
STEP 8. Check the injector.
1. Disconnect each injector connector.
2. Measure the resistance between injector side connector terminal No.1 and No.2.
Standard value: 2 - 3 Ohms [at 20 degrees C (68 degrees F)]
Q: Is the measured resistance between 2 and 3 Ohms [at 20 degrees C (68 degrees F)]?
YES: Go to Step 10.
NO: Replace the injector. Then go to Step 14.
STEP 9. Check harness connector C-121 at ECM for damage.
Q: Is the harness connector in good condition?
YES: Go to Step 10.
NO: Repair or replace it. Then go to Step 14.
STEP 10. Check for harness damage between injector connector and ECM connector.
a. Check the harness wire between injector connector B-22 (terminal No.2) and ECM connector C-121 (terminal No.1) at No.1 cylinder.
b. Check the harness wire between injector connector B-20 (terminal No.2) and ECM connector C-121 (terminal No.9) at No.2 cylinder.
c. Check the harness wire between injector connector B-18 (terminal No.2) and ECM connector C-121 (terminal No.24) at No.3 cylinder.
d. Check the harness wire between injector connector B-17 (terminal No.2) and ECM connector C-121 (terminal No.2) at No.4 cylinder.
Q: Is the harness wire in good condition?
YES: Go to Step 11.
NO: Repair it. Then go to Step 14.
STEP 11. Check the fuel pressure.
Refer to On-Vehicle Service - Fuel Pressure Test Testing and Inspection.
Q: Is the fuel pressure normal?
YES: Go to Step 12.
NO: Repair it. Then go to Step 14.
STEP 12. Check for entry of foreign matter (water, kerosene, etc.) into fuel.
Q: Are there any abnormalities?
YES: Replace the fuel. Then go to Step 14.
NO: Go to Step 13.
STEP 13. 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 20. OBD-II Drive Cycle Pattern Lists
3. Check the diagnostic trouble code (DTC).
Q: Is DTC P0171 set?
YES: Replace the ECM. Then go to Step 14.
NO: The inspection is complete.
STEP 14. 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 20. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0171 set?
YES: Retry the troubleshooting.
NO: The inspection is complete.