P0174
4GR-FSE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0171: System Too Lean (Bank 1)
DTC P0171 - System Too Lean (Bank 1)
DTC P0172 - System Too Rich (Bank 1)
DTC P0174 - System Too Lean (Bank 2)
DTC P0175 - System Too Rich (Bank 2)
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 trim.
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 ideal theoretical value. The long-term trim controls overall fuel compensation. The long-term fuel trim compensates for long-term deviations of the fuel trim from the ideal theoretical value. These long-term deviations result from the corrections made by the short-term fuel trim.
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 sets a DTC.
HINT:
- When DTC P0171 or P0174 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 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 or P0174 may be set. 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 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 as 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
Fuel-trim:
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:
Techstream only:
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 (A/F) sensor, Heated Oxygen (HO2) 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 Techstream.
1 Connect Techstream to the DLC3.
2 Start the engine and turn the tester on.
3 Warm up the engine at engine speed of 2500 rpm for approximately 90 seconds.
4 On the tester, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
5 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.)
6 Monitor the output voltages of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.
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.
NOTE:
The Air Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) 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 A/F and HO2 sensors.
- To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS Voltage B1 S1 and O2S B1 S2; then press the graph button on the Data List view.
HINT:
- Read freeze frame data using 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 Freeze Frame Data.
- 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 rich 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, P0172, P0174 OR P0175)
(a) Connect Techstream to the DLC3.
(b) Turn the engine switch on (IG) and turn the tester on.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(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
A -- Continue to next step.
2. CHECK PCV HOSE
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 leakage.
OK:
No leakage 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 Techstream to the DLC3.
(b) Start the engine and turn the tester on.
(c) Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
(d) On the tester, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
(e) 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).
(f) Monitor the output voltages of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.
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.
Result:
- 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.
C -- PERFORM CONFIRMATION DRIVING PATTERN
B -- INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
A -- Continue to next step.
5. READ VALUE USING ENGINE COOLANT TEMPERATURE SENSOR (COOLANT TEMP)
(a) Connect Techstream to the DLC3.
(b) Turn the engine switch on (IG) and turn the tester on.
(c) Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.
(d) Read the Coolant Temp twice, when the engine is both cold and warmed up.
Standard:
With cold engine
Same as ambient air temperature.
With warm engine
Between 75 and 95°C (167 and 203°F)
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK -- Continue to next step.
6. READ VALUE USING INTAKE AIR FLOW METER (MAF)
(a) Read the value using the Techstream (MAF).
NOTICE:
- Turn off the engine.
- Perform the inspection with the vehicle indoors and on a level surface.
- Perform the inspection of the MAF meter while it is installed to the air cleaner case (installed to the vehicle).
- During the test, do not use the exhaust air duct to perform suction on the exhaust pipe.
(1) Turn the engine switch on (ACC).
(2) Turn the engine switch on (IG) (do not run the engine).
(3) Turn the tester ON.
(4) Select the following menu items: Powertrain / Engine and ECT / Data List / MAF.
(5) Wait 30 seconds, and read the values on the Techstream.
Standard condition:
Less than 0.36 g/sec.
NG -- REPLACE MASS AIR FLOW METER
OK -- Continue to next step.
7. CHECK FUEL PRESSURE (LOW PRESSURE SIDE)
(a) Check the fuel pressure (low pressure side) Testing and Inspection.
NG -- CHECK AND REPLACE FUEL PUMP, PRESSURE REGULATOR, FUEL PIPE LINE AND FILTER
OK -- Continue to next step.
8. CHECK FUEL PRESSURE SENSOR
(a) Connect Techstream to the DLC3.
(b) Turn the engine switch on (IG) and turn the tester on.
(c) Start the engine.
(d) Enter the following menus: Powertrain / Engine and ECT / Data List / Fuel Press.
(e) While revving the engine, check that the fuel pressure fluctuates.
OK:
Fuel pressure fluctuates.
NG -- REPLACE FUEL PRESSURE SENSOR
OK -- Continue to next step.
9. CHECK FUEL PRESSURE (HIGH PRESSURE SIDE)
(a) Check the fuel pressure (high pressure side) Testing and Inspection.
NG -- CHECK AND REPLACE FUEL PUMP, FUEL PRESSURE SENSOR, WIRING AND FUEL LEAKAGE
OK -- Continue to next step.
10. CHECK FOR EXHAUST GAS LEAK
OK:
No gas leakage.
NG -- REPAIR OR REPLACE EXHAUST SYSTEM
OK -- Continue to next step.
11. CHECK FOR SPARK AND IGNITION
HINT:
If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Rate (to Cylinder #6 Misfire Rate).
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
12. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the E42 or E38 A/F sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance (Bank 1 sensor 1):
Standard resistance (Bank 2 sensor 1):
(c) Reconnect the A/F sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.
13. INSPECT A/F RELAY
(a) Remove the A/F relay from the engine room R/B No. 2.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reinstall the A/F relay.
NG -- REPLACE A/F RELAY
OK -- Continue to next step.
14. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
(a) Disconnect the E42 and E38 A/F sensor connectors.
(b) Turn the engine switch on (IG).
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage:
(d) Turn the engine switch off.
(e) Disconnect the E6 ECM connector.
(f) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(g) Reconnect the ECM connector.
(h) Reconnect the A/F sensor connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
15. REPLACE AIR FUEL RATIO SENSOR
NEXT -- Continue to next step.
16. PERFORM CONFIRMATION DRIVING PATTERN
(a) Connect Techstream to the DLC3. (Procedure "A")
(b) Turn the engine switch on (IG) and turn the tester on. (Procedure "B")
(c) Clear DTCs DTC Check / Clear. (Procedure "C")
(d) Switch the ECM from normal mode to check mode using the tester Check Mode Procedure. (Procedure "D")
(e) Start the engine and warm it up with all the accessories switched OFF. (Procedure "E")
(f) Drive the vehicle at between 38 mph and 75 mph (60 km/h and 120 km/h) and at an engine speed of between 1400 rpm and 3200 rpm for 3 to 5 minutes. (Procedure "F")
HINT:
If the system is still malfunctioning, the MIL will be illuminated during procedure "F".
NOTE:
If the conditions in this test are not strictly followed, no malfunction will be detected.
NEXT -- Continue to next step.
17. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)
(a) On Techstream, enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(b) Read DTCs.
Result:
B -- READ VALUE USING ENGINE COOLANT TEMPERATURE SENSOR (COOLANT TEMP)
A -- END