P0171
2AR-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 duration. 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 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 both 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 stores a DTC.
HINT
* When DTC P0171 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 is stored, 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 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 fuel injection volumes estimated by the ECM 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 thresholds, the ECM interprets this as a fault in the fuel system and stores a DTC.
Example:
The average fuel trim learned value is more than +35% or less than -35%, 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 the DTCs (even if no DTCs are stored, perform the clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.
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 between 37 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.
9. Enter the following menus: Powertrain / Engine / Trouble Codes / Pending.
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 P0136 P0136.
Refer to DTC P2195 P2195.
INSPECTION PROCEDURE
HINT
Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using the Techstream.
(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 / Active Test / Control the Injection Volume for A/F Sensor.
(f) Perform the Active Test 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) 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.
NOTICE:
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.
- Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.
- To display the graph, enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS Voltage B1S1 and O2S B1S2; then press the graph button on the Data List view.
NOTICE:
Inspect the fuses for circuits related to this system before performing the following inspection procedure.
HINT
* Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
* 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 ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)
(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 / Trouble Codes.
(e) Read the DTCs.
Result:
HINT
If any DTCs other than P0171 or P0172 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 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 INTAKE SYSTEM
(a) Check the intake system for vacuum leaks Intake System.
OK:
No leaks from intake system.
NG -- REPAIR OR REPLACE INTAKE SYSTEM
OK -- Continue to next step.
4. PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)
(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 / 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 voltage outputs of the air fuel ratio sensor and the heated oxygen 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.
* 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.
Standard:
Result
Lean: During Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.
Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently below 3.1 V, and the O2S is consistently higher 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.
C -- PERFORM CONFIRMATION DRIVING PATTERN
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.
(c) Turn the Techstream on.
(d) Enter the following menus: Powertrain / Engine / Data List / All Data / Coolant Temp.
(e) Read the Data List twice, when the engine is both cold and warmed up.
Standard Value:
With cold engine: Same as ambient air temperature.
With warm engine: 80 to 100°C (176 to 212°F).
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR Removal
OK -- Continue to next step.
6. INSPECT MASS AIR FLOW METER
(a) Inspect the mass air flow meter Inspection.
NG -- REPLACE MASS AIR FLOW METER Removal
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 leak from the exhaust manifold sub-assembly and exhaust pipes.
OK:
No gas leak.
NG -- REPAIR OR REPLACE EXHAUST GAS LEAK POINT
OK -- Continue to next step.
9. CHECK SPARK AND IGNITION
HINT
* Refer to the ignition system inspection procedure Testing and Inspection.
* 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 / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
- Refer to the fuel injector inspection procedure Testing and Inspection.
- If the fuel injectors malfunction, engine misfire may occur. The misfire count can be read using the Techstream. Enter the following menus: Powertrain / Engine / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
NG -- REPLACE FUEL INJECTOR ASSEMBLY Removal
OK -- PERFORM CONFIRMATION DRIVING PATTERN
11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the air fuel ratio sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
(c) Reconnect the air fuel ratio sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR Removal
OK -- Continue to next step.
12. CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)
(a) Disconnect the air fuel ratio sensor connector.
(b) Turn the ignition switch to ON.
(c) Measure the voltage according to the value(s) in the table below.
Standard Voltage:
(d) Reconnect the air fuel ratio sensor connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - ENGINE ROOM JUNCTION BLOCK ASSEMBLY)
OK -- Continue to next step.
13. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)
(a) Disconnect the air fuel ratio sensor connector.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance (Check for Open):
Standard Resistance (Check for Short):
(d) Reconnect the air fuel ratio sensor connector.
(e) Reconnect the ECM connector.
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 to ON and turn the Techstream on.
(c) Clear the DTCs (even if no DTCs are stored, perform the Clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.
(d) Turn the ignition switch off and wait for at least 30 seconds.
(e) Turn the ignition switch to ON and turn the Techstream on.
(f) 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.
(g) Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
NEXT -- Continue to next step.
16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)
(a) Enter the following menus: Powertrain / Engine / Trouble Codes / Pending.
(b) Read the pending DTCs.
Result:
B -- REPLACE ECM Removal
A -- END
17. PERFORM CONFIRMATION DRIVING PATTERN
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON and turn the Techstream on.
(c) Clear the DTCs (even if no DTCs are stored, perform the Clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.
(d) Turn the ignition switch off and wait for at least 30 seconds.
(e) Turn the ignition switch to ON and turn the Techstream on.
(f) 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.
(g) Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
NEXT -- Continue to next step.
18. CHECK WHETHER DTC OUTPUT RECURS (DTC O0171 OR P0172)
(a) Enter the following menus: Powertrain / Engine / Trouble Codes / Pending.
(b) Read the pending DTCs.
Result:
B -- REPLACE ECM Removal
A -- CHECK FOR INTERMITTENT PROBLEMS Check for Intermittent Problems