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.
DTC SET CONDITIONS
Check Conditions
- Engine coolant temperature is lower than approximately 100 °C (212 °F) when the engine is started.
- Intake air temperature is lower than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 77 °C (171 °F).
- Volume airflow sensor output frequency is 56 Hz 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 approximately 100 °C (212 °F) when the engine is started.
- Intake air temperature is lower than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 77 °C (171 °F).
- Volume airflow sensor output frequency is 56 Hz 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 approximately 100 °C (212 °F) when the engine is started.
- Intake air temperature is higher than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 77 °C (171 °F).
- Volume airflow sensor output frequency is 56 Hz 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 +20.0 percent for 5 seconds.
Check Conditions
- Engine coolant temperature is higher than approximately 100 °C (212 °F) when the engine is started.
- Intake air temperature is higher than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 77 °C (171 °F).
- Volume airflow sensor output frequency is 56 Hz 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 77 °C (171 °F).
- Under the closed loop air/fuel ratio control.
Judgement 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.
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:
- MB991502: Scan Tool (MUT-II)
- MB991958: Scan Tool (MUT-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 MB991502 or MB991958, check data list item 12: Volume Airflow Sensor.
CAUTION: To prevent damage to scan tool MB991502 or MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502 or MB991958.
1. Connect scan tool MB991502 or MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 or MB991958 to the data reading mode for item 12, Volume Airflow Sensor.
4. Warm up the engine to normal operating temperature: 80 °C to 95 °C (176 °F to 203 °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 MB991502 or MB991958, check data list item 13: Intake Air Temperature Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991502 or 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 MB991502 or MB991958, check data list item 21: Engine Coolant Temperature Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991502 or 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 MB991502 or MB991958, check data list item 25: Barometric Pressure Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991502 or 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 P0106 - Barometric Pressure Circuit Range/Performance Problem, DTC P0107 - Barometric Pressure Circuit Low Input, DTC P0108 - Barometric Pressure Circuit High Input.
STEP 7. Check connectors B-17, B-18, B-20, B-22 at injector for damage.
Q: Is the connector in good condition?
YES: Go to Step 8.
NO: Repair or replace it. Refer to Harness Connector Inspection. 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 °C (68 °F)]
Q: Is the resistance between 2 and 3 Ohms [at 20 °C (68 °F)]?
YES: Go to Step 10.
NO: Replace the injector. Then go to Step 14.
STEP 9. Check connector C-121 at ECM for damage.
Q: Is the connector in good condition?
YES: Go to Step 10.
NO: Repair or replace it. Refer to Harness Connector Inspection. 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. 14) at No. 2 cylinder.
c. Check the harness wire between injector connector B-18 (terminal No. 2) and ECM connector C-121 (terminal No. 2) at No. 3 cylinder.
d. Check the harness wire between injector connector B-17 (terminal No. 2) and ECM connector C-121 (terminal No. 15) 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.
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 - Procedure 2 - Fuel Trim Monitor.
3. Check the diagnostic trouble code (DTC).
Q: Is DTC P0171 set?
YES: Replace the ECM. Then go to Step 14.
NO: The procedure is complete.
STEP 14. Perform 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.
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0171 set?
YES: Repeat the troubleshooting.
NO: The procedure is complete.