P0171
1GR-FE ENGINE CONTROL: SFI SYSTEM: P0171, P0172, P0174, P0175: 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 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 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.
HINT
* When DTC P0171 or P0174 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is stored, the actual air-fuel ratio is on the rich side.
* If the vehicle runs out of fuel, the air-fuel ratio becomes lean and DTC P0171 or P0174 may be stored. The MIL is then illuminated.
* When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is higher 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 learned value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learned value of the air-fuel ratio). If the average fuel trim learned value exceeds the malfunction threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.
Example:
If the average fuel trim learned 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
1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON and turn the Techstream on.
3. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
4. Turn the ignition switch off and wait for at least 30 seconds.
5. Turn the ignition switch to ON and turn the Techstream on [A].
6. 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].
7. With the engine warmed up, idle the engine for 2 minutes or more [C].
8. Drive the vehicle at a speed between 60 and 135 km/h (38 and 85 mph) for 5 minutes or more [D].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [E].
10. Read pending DTCs.
HINT
If a pending DTC is output, the system is malfunctioning.
11. If no pending DTC is output, perform a universal trip and check for permanent DTCs Reading and Clearing Diagnostic Trouble Codes.
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 P0102 P0102.
Refer to DTC P2195 P2195.
INSPECTION PROCEDURE
NOTICE:
Inspect the fuses for circuits related to this system before performing the following inspection procedure.
HINT
* Read freeze frame data using the Techstream. Freeze frame data records 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 air fuel ratio sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run rich.
* A high air fuel ratio 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 FOR ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)
(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 / Trouble Code.
(d) Read DTCs.
Result
HINT
If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.
B -- GO TO DTC CHART SFI System
A -- Continue to next step.
2. CHECK PCV HOSE CONNECTIONS
(a) Check the PCV hose connections.
OK:
PCV hose is connected correctly and is not damaged.
NG -- REPAIR OR REPLACE PCV HOSE Removal
OK -- Continue to next step.
3. CHECK AIR INDUCTION SYSTEM
(a) Check the air induction system for vacuum leakage.
OK:
No leakage from air induction system.
NG -- REPAIR OR REPLACE AIR INDUCTION SYSTEM Removal
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 idling (press the RIGHT or LEFT button to change the fuel injection volume).
(g) Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) 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.
* The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.
Result
Lean: During the Control the Injection Volume for A/F Sensor Active Test, the air fuel ratio sensor output voltage (AFS Voltage) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.
Rich: During the Control the Injection Volume for A/F Sensor Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.
Lean/Rich: During the Control the Injection Volume for A/F Sensor 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 / Coolant Temp.
(d) Read Coolant Temp twice, when the engine is cold and when it is warmed up.
Standard:
With cold engine: Same as ambient air temperature.
With warm engine: Between 75°C and 100°C (167°F and 212°F).
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR Removal
OK -- Continue to next step.
6. READ VALUE USING TECHSTREAM (MAF)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the Techstream on.
(d) Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF, Coolant Temp and Engine speed.
(e) Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.
(f) Read MAF with the engine speed at 3000 rpm.
Standard:
Between 13.8 g/sec. and 17.3 g/sec. (shift lever: N; A/C: Off).
NG -- CHECK HARNESS AND CONNECTOR
OK -- Continue to next step.
7. CHECK FUEL PRESSURE
(a) Check the fuel pressure Fuel System.
NG -- REPAIR OR REPLACE FUEL SYSTEM
OK -- Continue to next step.
8. CHECK FOR EXHAUST GAS LEAK
(a) Check for exhaust gas leakage.
OK:
No gas leakage.
NG -- REPAIR OR REPLACE EXHAUST SYSTEM
OK -- Continue to next step.
9. CHECK FOR SPARKS AND IGNITION
(a) Check for sparks and ignition Testing and Inspection.
HINT
If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count).
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
(a) Check the fuel injector assembly Testing and Inspection.
HINT
If the injectors malfunction, engine misfire may occur. The misfire count can be read using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count).
OK -- PERFORM CONFIRMATION DRIVING PATTERN
NG -- REPLACE FUEL INJECTOR ASSEMBLY Removal
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 AIR FUEL RATIO SENSOR) P0031
NG -- CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY)
OK -- Continue to next step.
13. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM) P2195
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
14. REPLACE AIR FUEL RATIO SENSOR
(a) Replace the air fuel ratio 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 the DTCs Reading and Clearing Diagnostic Trouble Codes.
(e) Turn the ignition switch off and wait for at least 30 seconds.
(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 Confirmation Driving Pattern.
(i) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(j) Input the DTC: P0171, P0172, P0174 or P0175.
(k) Check the DTC judgment result.
Result
NEXT -- Continue to next step.
16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)
(a) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(b) Input the DTC: P0171, P0172, P0174 or P0175.
(c) Check that DTC MONITOR is NORMAL.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code / Pending.
(e) Read Pending DTCs.
Result
B -- END
A -- Continue to next step.
17. CHECK HARNESS AND CONNECTOR
(a) Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM Electronic Circuit Inspection Procedure.
HINT
Repair any problems.
NEXT -- Continue to next step.
18. PERFORM CONFIRMATION DRIVING PATTERN
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON.
(c) Turn the Techstream on.
(d) Clear the DTCs Reading and Clearing Diagnostic Trouble Codes.
(e) Turn the ignition switch off and wait for at least 30 seconds.
(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 Confirmation Driving Pattern.
(i) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(j) Input the DTC: P0171, P0172, P0174 or P0175.
(k) Check the DTC judgment result.
Result
NEXT -- Continue to next step.
19. CHECK WHETHER DTC OUTPUT RECURS
(a) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(b) Input the DTC: P0171, P0172, P0174 or P0175.
(c) Check that DTC MONITOR is NORMAL.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code / Pending.
(e) Read Pending DTCs.
Result
B -- END
A -- Continue to next step.
20. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)
(a) Disconnect the mass air flow meter connector.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
(d) Reconnect the mass air flow meter connector.
(e) Reconnect the ECM connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
21. REPLACE MASS AIR FLOW METER
(a) Replace the mass air flow meter assembly Removal.
HINT
If the result of the inspection performed in step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter assembly.
NEXT -- Continue to next step.
22. PERFORM CONFIRMATION DRIVING PATTERN
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON.
(c) Turn the Techstream on.
(d) Clear the DTCs Reading and Clearing Diagnostic Trouble Codes.
(e) Turn the ignition switch off and wait for at least 30 seconds.
(f) Turn the ignition switch to 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 Confirmation Driving Pattern.
(i) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(j) Input the DTC: P0171, P0172, P0174 or P0175.
(k) Check the DTC judgment result.
Result
NEXT -- Continue to next step.
23. CHECK WHETHER DTC OUTPUT RECURS
(a) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
(b) Input the DTC: P0171, P0172, P0174 or P0175.
(c) Check that DTC MONITOR is NORMAL.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code / Pending.
(e) Read Pending DTCs.
Result
B -- REPLACE ECM Removal
A -- END
24. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY) P0031
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE NO. 1 INTEGRATION RELAY Testing and Inspection