Toyota Tundra Service Manual: System Too Lean (Bank 1) (P0171,P0172,P0174,P0175)

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 is 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 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 stores a DTC.

Example:

If 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

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 between 60 and 120 km/h (37 and 75 mph) 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 and ECT / Trouble Codes [E].
10. Read the pending DTCs.

    HINT:

    • If a pending DTC is output, the system is malfunctioning.
    • If a pending DTC is not output, perform the following procedure.
11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
12. Input the DTC: P0171, P0172, P0174 or P0175.
13. Check the DTC judgment result.

    Tester Display	Description
    NORMAL	DTC judgment completed System normal
    ABNORMAL	DTC judgment completed System abnormal
    INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
    N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

    HINT:

    If the judgment result shows INCOMPLETE or N/A, perform steps [C] through [E] again.

14. If no pending DTC is output, perform a universal trip and check for permanent DTCs (See page ).

    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 (See page ).

CAUTION / NOTICE / HINT

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.
• Bank 1 refers to the bank that includes the No. 1 cylinder*.

  *: The No. 1 cylinder is the cylinder which is farthest from the transmission.

• Bank 2 refers to the bank that does not include the No. 1 cylinder.
• Sensor 1 refers to the sensor closest to the engine assembly.
• Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE

(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 / Trouble Codes.

(e) Read DTCs.

HINT:

If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.

B

GO TO DTC CHART

A

(a) Check the PCV hose connections (See page ).

OK:

PCV hose is connected correctly and is not damaged.

NG

REPAIR OR REPLACE PCV HOSE

OK

HINT:

If a malfunction occurs when depressing the brake pedal, inspect the brake booster assembly, as there may be a vacuum leak in the brake booster assembly itself.

(a) Check the intake system for vacuum leaks (See page ).

OK:

No leaks in intake system.

HINT:

Perform "Inspection After Repair" after repairing or replacing the intake system (See page ).

NG

REPAIR OR REPLACE INTAKE SYSTEM

OK

(a) Connect the Techstream to the DLC3.

(b) Start the engine.

(c) Turn the Techstream on.

(d) Warm up the engine and run 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.

(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:

• Change the fuel injection volume within the range of -12.5% to +12.5%.
• 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.
• If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

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

GO TO STEP 11

A

(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 / Coolant Temp.

(e) Read 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°C and 100°C (167°F and 212°F).

HINT:

Perform "Inspection After Repair" after replacing the engine coolant temperature sensor (See page ).

NG

REPLACE ENGINE COOLANT TEMPERATURE SENSOR

OK

(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 / MAF and Coolant Temp.

(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 18.3 gm/sec. and 25.8 gm/sec. (shift lever: N; A/C: Off).

NG

GO TO STEP 18

OK

(a) Check the fuel pressure (See page ).

HINT:

Perform "Inspection After Repair" after repairing or replacing the fuel system (See page ).

NG

REPAIR OR REPLACE FUEL SYSTEM

OK

(a) Check for exhaust gas leak.

OK:

No gas leak.

HINT:

Perform "Inspection After Repair" after repairing or replacing the exhaust system (See page ).

NG

REPAIR OR REPLACE EXHAUST SYSTEM

OK

(a) Perform the spark test (See page ).

OK:

Sparks jump across electrode gap.

HINT:

Perform "Inspection After Repair" after repairing or replacing the ignition system (See page ).

NG

REPAIR OR REPLACE IGNITION SYSTEM

OK

(a) Check the injection and volume.

HINT:

• Refer to the fuel injector assembly inspection procedure (See page ).
• 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 / Cylinder #1 Misfire Count (to Cylinder #8 Misfire Count).
• Perform "Inspection After Repair" after replacing the fuel injector assembly (See page ).

OK

GO TO STEP 15

NG

REPLACE FUEL INJECTOR

NG

REPLACE AIR FUEL RATIO SENSOR

OK

NG

GO TO STEP 23

OK

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Replace the air fuel ratio sensor (See page ).

HINT:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor (See page ).

NEXT

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(c) Turn the Techstream on.

(d) Clear the DTCs (See page ).

(e) Turn the ignition switch off.

(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 / Trouble Codes.

(j) Read DTCs.

B

END

A

(a) Connect the Techstream to the DLC3.

(b) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

• When performing the Active Test, make sure the shift lever is in P or N.
• The A/C switch and all accessory switches should be off.

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

(e) Confirm that Throttle Idle Position is ON and check the engine idling condition and the value of MAP in the Data List while performing the Active Test.

HINT:

• Do not leave the EGR valve open for 10 seconds or more during the Active Test.
• Be sure to return the EGR valve to step 0 when the Active Test is completed.

OK:

MAP and idling condition change in response to EGR step position as follows.

Standard:

OK

GO TO STEP 18

NG

(a) Remove the EGR valve assembly (See page ).

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly (See page ).

NG

REPLACE EGR VALVE ASSEMBLY

OK

(a) Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM (See page ).

HINT:

Repair any problems.

NEXT

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(c) Turn the Techstream on.

(d) Clear the DTCs (See page ).

(e) Turn the ignition switch off.

(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 / Trouble Codes.

(j) Read DTCs.

B

END

A

(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:

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Replace the mass air flow meter (See page ).

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.
• Perform "Inspection After Repair" after replacing the mass air flow meter (See page ).

NEXT

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(c) Turn the Techstream on.

(d) Clear the DTCs (See page ).

(e) Turn the ignition switch off.

(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 / Trouble Codes.

(j) Read DTCs.

A

END

B

REPLACE ECM

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Inspect the integration relay (A/F) (See page ).

OK

CHECK ECM POWER SOURCE CIRCUIT

NG

REPLACE INTEGRATION RELAY