P0171
System 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
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 air flow sensor output frequency is 81 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 °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 air flow sensor output frequency is 81 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 °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 air flow sensor output frequency is 81 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 °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 air flow sensor output frequency is 81 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 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.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Volume air flow 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.
- ECU failed.
- PCM failed.
DIAGNOSIS
Required Special Tools
- MB991502: Scan Tool (MUT-II)
STEP 1. Check the exhaust leaks.
Q: Are there any abnormalities?
YES: Go to Step 2.
NO: Repair it. Then go to Step 14.
STEP 2. Check the intake system vacuum leak.
Q: Are there any abnormalities?
YES: Go to Step 3.
NO: Repair it. Then go to Step 14.
STEP 3. Using scan tool MB991502, check data list item 12: Volume Air Flow Sensor.
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector
2. Start the engine and run at idle.
3. Set scan tool MB991502 to the data reading mode for item 12, Volume Air Flow 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 g/s).
- When 2,500 r/min, between 70 and 110 Hz (between 6.6 and 10.2 g/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 Air Flow Circuit Range/Performance Problem, DTC P0102 - Volume Air Flow Circuit Low Input.
STEP 4. Using scan tool MB991502, check data list item 13: Intake Air Temperature Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991502 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, check data list item 21: Engine Coolant Temperature Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991502 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, check data list item 25: Barometric Pressure Sensor.
1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991502 to the data reading mode for item 25, Barometric Pressure Sensor.
- When altitude is 0 m (0 foot), 101 kPa.
- When altitude is 600 m (1,969 feet), 95 kPa.
- When altitude is 1,200 m (3,937 feet), 88 kPa.
- When altitude is 1,800 m (5,906 feet), 81 kPa.
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 connector 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 1 and 2.
Standard value: 13 - 16 ohm [at 20 °C (68 °F)]
Q: Is the resistance standard value?
YES: Go to Step 9.
NO: Replace the injector. Then go to Step 14.
STEP 9. Check connector C-121 at ECM
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 2 and ECM connector C-121 terminal 1
b. Check the harness wire between injector connector B-20 terminal 2 and ECM connector C-121 terminal 14
c. Check the harness wire between injector connector B-18 terminal 2 and ECM connector C-121 terminal 2
d. Check the harness wire between injector connector B-17 terminal 2 and ECM connector C-121 terminal 15
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, Fuel Pressure Test.
Q: Is the fuel pressure normal?
YES: Go to Step 12.
NO: Repair or replace 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: Go to Step 13.
NO: Replace the fuel. Then go to Step 14.
STEP 13. Replace the injector.
1. Replace the injector.
2. Carry out a test drive with the drive cycle pattern. Refer to, Procedure 2 - Fuel Trim Monitor.
3. Check the diagnostic trouble code (DTC).
Q: Is the DTC P0171 output?
YES: Replace the ECM or PCM. 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, Procedure 2 - Fuel Trim Monitor.
2. Check the diagnostic trouble code (DTC).
Q: Is the DTC P0171 output?
YES: Retry the troubleshooting.
NO: The inspection is complete.