P0171
DTC P0171: System too LeanFuel Trim Circuit
- Refer to, DTC P0201 - P0204 Injector Circuit.
CIRCUIT OPERATION
- Refer to, DTC P0201 - P0204 Injector Circuit.
TECHNICAL DESCRIPTION
- If a malfunction occurs in the fuel system, the fuel trim value becomes too large.
- The ECM
DESCRIPTIONS OF MONITOR METHODS
Air/fuel learning value (long time fuel trim) and air/ fuel feedback integral value (short time 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)
- Mass 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 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).
- Mass airflow sensor output is 9 g/sec or more.
Judgement 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 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).
- Mass airflow sensor output is 9 g/sec or less.
Judgement 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 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).
- Mass airflow sensor output is 9 g/sec or more.
Judgement 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 than +20.0 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is higher than 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).
- Mass airflow sensor output is 9 g/sec or less.
Judgement 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.
Judgement Criteria
- Long-term fuel trim has continued to be higher than +12.5 percent for 2 seconds.
or
- Short-term fuel trim has continued to be higher than +25.0 percent for 2 seconds.
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 19 OBD-II Drive Cycle Pattern Lists.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Mass airflow sensor failed.
- Injector failed.
- Incorrect fuel pressure.
- Air drawn in from gaps in gasket, seals, etc.
- Engine coolant temperature sensor failed.
- Intake air temperature sensor failed.
- Manifold absolute pressure sensor failed.
- Barometric pressure sensor failed.
- Exhaust leak.
- Use of incorrect or contaminated fuel.
- Harness damage in injector circuit or connector damage.
- 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. Check for exhaust leak.
Q: Are there any abnormalities?
YES: Repair it. Then go to Step 15.
NO: Go to Step 2.
STEP 2. Check for intake system vacuum leak.
Q: Are there any abnormalities?
YES: Repair it. Then go to Step 15.
NO: Go to Step 3.
STEP 3. Using scan tool MB991958, check data list item 12: Mass 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, Mass Airflow Sensor.
4. Warm up the engine to normal operating temperature: 85 degrees C to 95 degrees C (185 degrees F to 203 degrees F).
- When idling, between 2.0 and 6.0 g/sec.
- When 2,500 r/min, between 8.0 and 16.0 g/sec.
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 - Mass Airflow Circuit Range/ Performance Problem, DTC P0102 - Mass Airflow Circuit Low Input, DTC P0103 - Mass Airflow Circuit High 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. Using scan tool MB991958, check data list item 95: 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 95, 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.
- When the engine is idling, 16 - 36 kPa (4.7 - 10.6 in.Hg).
- When the engine is suddenly revved, manifold absolute pressure increases.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 8.
NO: 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 8. Check harness connector B-17, B-18, B-20, B-22 at injector for damage.
Q: Is the harness connector in good condition?
YES: Go to Step 9.
NO: Repair or replace it. Then go to Step
STEP 9. Check the injector.
1. Disconnect each injector connector.
2. Measure the resistance between injector side connector terminal No. 1 and No. 2.
Standard value: 10.5 - 13.5 Ohms [at 20 degrees C (68 degrees F)]
Q: Is the measured resistance between 10.5 and 13.5 Ohms?
YES: Go to Step 10.
NO: Replace the injector. Then go to Step 15.
STEP 10. Check harness connector C-133 at ECM
Q: Is the harness connector in good condition?
YES: Go to Step 11.
NO: Repair or replace it. Then go to Step 15.
STEP 11. Check for harness damage between injector connector and ECM
a. Check the harness wire between injector connector B-22 (terminal No. 2) and ECM connector C-133
b. Check the harness wire between injector connector B-20 (terminal No. 2) and ECM connector C-133
c. Check the harness wire between injector connector B-18 (terminal No. 2) and ECM connector C-133
d. Check the harness wire between injector connector B-17 (terminal No. 2) and ECM connector C-133
Q: Is the harness wire in good condition?
YES: Go to Step 12.
NO: Repair it. Then go to Step 15.
STEP 12. 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 13.
NO: Repair or replace it. Then go to Step 15.
STEP 13. Check for entry of foreign matter (water, kerosene, etc.) into fuel.
Q: Are there any abnormalities?
YES: Replace the fuel. Then go to Step 15.
NO: Go to Step 14.
STEP 14. 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 19 OBD-II Drive Cycle Pattern Lists.
3. Check the diagnostic trouble code (DTC).
Q: Is DTC P0171 set?
YES: Replace the ECM or the PCM. Then go to Step 15.
NO: The inspection is complete.
STEP 15. 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 19 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.