P0171
1NZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0171,P0172: System Too Lean (Bank 1)
DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both the short-term and the long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.
Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.
If the total of the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.
HINT
- When DTC P0171 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 is set, the actual air-fuel ratio is on the rich side.
- If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 may be set. The MIL is then illuminated.
- When the total of the short-term and long-term fuel trim values is within 20 % (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.
MONITOR DESCRIPTION
Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the ECM's estimated fuel injection volumes also affect the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air-fuel ratio). If the average fuel trim learning value exceeds the malfunction threshold, the ECM interprets this a fault in the fuel system and sets a DTC.
Example:
The average fuel trim learning value is +35 % or more or -35 % or less, the ECM interprets this as a fuel system malfunction.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
CONFIRMATION DRIVING PATTERN
* Connect the Techstream to the DLC3.
* Turn the ignition switch to ON and turn the Techstream on.
* Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
* Turn the ignition switch off and wait for at least 30 seconds.
* Turn the ignition switch to ON and turn the Techstream on [A].
* Start the engine and warm it up (until the engine coolant temperature is 75°C (167°F) or higher) with all the accessories switched off [B].
* With the engine warmed up, idle the engine for 2 minutes or more [C].
* Drive the vehicle at between 38 and 75 mph (60 and 120 km/h) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more [D].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
* Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [E].
* Read pending DTCs.
HINT
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC is not output, perform the following procedure.
* Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
* Input the DTC: P0171 or P0172.
* Check the DTC judgment result.
HINT
If the judgment result shows INCOMPLETE or UNKNOWN, perform steps [C] through [E] again.
* If no pending DTC is output, perform a universal trip and check for permanent DTCs DTC Check / Clear.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
WIRING DIAGRAM
Refer to DTC P2195 P2195.
INSPECTION PROCEDURE
HINT
- Read freeze frame data using a Techstream. Freeze frame data record the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data, from the time the malfunction occurred.
- A low A/F sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run rich.
- A high A/F sensor voltage could be caused by a lean air-fuel mixture. Check for conditions that would cause the engine to run lean.
PROCEDURE
1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)
(a) Connect a Techstream to the DLC3.
(b) Turn the ignition switch to ON and turn the Techstream on.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(d) Read DTCs.
Result:
HINT
If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.
B -- GO TO DTC CHART Engine Control System - SFI System
A -- Continue to next step.
2. CHECK PCV HOSE CONNECTIONS
(a) Check the PCV hose connections Testing and Inspection.
OK:
PCV hose is connected correctly and is not damaged.
NG -- REPAIR OR REPLACE PCV HOSE
OK -- Continue to next step.
3. CHECK AIR INDUCTION SYSTEM
(a) Check the air induction system for vacuum leak.
OK:
No leak from air induction system.
NG -- REPAIR OR REPLACE AIR INDUCTION SYSTEM
OK -- Continue to next step.
4. PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL)
(a) Connect the Techstream to the DLC3.
(b) Start the engine.
(c) Turn the Techstream on.
(d) Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
(e) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
(f) Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
(g) Monitor the voltage outputs of the Air-Fuel Ratio (A/F) sensor and the Heated Oxygen (HO2) sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.
HINT
- The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
- Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
Standard:
Result:
Result::
(h) Lean: During Control the Injection Volume for A/F Sensor, the A/F sensor output voltage (AFS) is consistently more than 3.4 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.
Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.
Lean/Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor alternates correctly.
B -- INSPECT AIR-FUEL RATIO SENSOR (HEATER RESISTANCE)
A -- Continue to next step.
5. READ VALUE USING TECHSTREAM (COOLANT TEMP)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON and turn the Techstream on.
(c) Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.
(d) Read the Data List twice, when the engine is both cold and warmed up.
Standard:
With cold engine: Same as ambient air temperature.
With warm engine: 75°C to 100°C (167°F to 212°F).
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK -- Continue to next step.
6. READ VALUE USING TECHSTREAM (MAF)
(a) Read the values using the Techstream (MAF).
NOTICE:
- Turn the ignition switch off.
- Perform the inspection with the vehicle indoors and on a level surface.
- Perform the inspection of the mass air flow meter while it is installed in the air cleaner case (installed on the vehicle).
- During the test, do not use an exhaust air duct to apply suction to the exhaust pipe.
(1) Connect the Techstream to the DLC3.
(2) Turn the ignition switch ON (do not start the engine).
(3) Turn the Techstream on.
(4) Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.
(5) Wait for 30 seconds, and read the values on the Techstream.
Standard value:
Less than 0.28 g/sec
(b) Inspect the mass air flow meter.
(1) Remove the mass air flow meter Removal.
(2) Using a work light, check that the platinum filament (heater portion) in the mass air flow meter has no foreign matter attached.
OK:
No foreign matter attached
(3) Reinstall the mass air flow meter Installation.
NG -- REPLACE MASS AIR FLOW METER Removal
OK -- Continue to next step.
7. CHECK FOR SPARKS AND IGNITION P0300
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
8. CHECK FOR EXHAUST GAS LEAK
(a) Check for exhaust gas leak.
OK:
No gas leak.
NG -- REPAIR OR REPLACE EXHAUST SYSTEM
OK -- Continue to next step.
9. CHECK FUEL PRESSURE
(a) Check the fuel pressure Testing and Inspection.
Standard:
304 to 343 kPa (3.1 to 3.5 kgf/cm2, 44.1 to 49.7 psi)
NG -- REPAIR OR REPLACE FUEL SYSTEM
OK -- Continue to next step.
10. INSPECT FUEL INJECTOR (INJECTION AND VOLUME)
(a) Check the injection volume Testing and Inspection.
Standard:
45 to 58 cm3 (2.9 to 3.5 cu in.) per 15 seconds
NG -- REPLACE FUEL INJECTOR Removal
OK -- PERFORM CONFIRMATION DRIVING PATTERN
11. INSPECT AIR-FUEL RATIO SENSOR (HEATER RESISTANCE) P0031
NG -- REPLACE AIR-FUEL RATIO SENSOR Removal
OK -- Continue to next step.
12. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR) P0031
NG -- CHECK HARNESS AND CONNECTOR (A/F SENSOR - INTEGRATION RELAY)
OK -- Continue to next step.
13. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM) P2195
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
14. REPLACE AIR-FUEL RATIO SENSOR
(a) Replace the A/F sensor Removal.
NEXT -- Continue to next step.
15. PERFORM CONFIRMATION DRIVING PATTERN
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON.
(c) Turn the Techstream on.
(d) Clear DTCs DTC Check / Clear.
(e) Turn the ignition switch off.
(f) Turn the ignition switch ON and turn the Techstream on.
(g) Start the engine and warm it up.
(h) Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
(i) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(j) Input the DTC: P0171 or P0172.
(k) Check the DTC judgment result.
Result:
B -- END
A -- Continue to next step.
16. REPLACE ECM
(a) Replace the ECM Removal.
NEXT -- Continue to next step.
17. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON.
(c) Turn the Techstream on.
(d) Clear DTCs DTC Check / Clear.
(e) Turn the ignition switch off.
(f) Turn the ignition switch ON and turn the Techstream on.
(g) Start the engine and warm it up.
(h) Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
(i) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(j) Input the DTC: P0171 or P0172.
(k) Check the DTC judgment result.
NEXT -- END
18. CHECK HARNESS AND CONNECTOR (A/F SENSOR - INTEGRATION RELAY) P0031
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPAIR OR REPLACE ECM POWER SOURCE CIRCUIT