Repair Manual: 2ZR-FXE Engine Control • SFI System • P0171, P0172

P0171 System Too Lean (Bank 1)

P0172 System Too Rich (Bank 1)

DESCRIPTION

Fuel trim relates to the feedback compensation value, not the basic injection duration. It consists of short-term and long-term fuel trim.

Short-term fuel trim is fuel compensation used to maintain the air-fuel ratio at stoichiometric levels. The air fuel ratio sensor signal indicates if the ratio is rich or lean, triggering adjustments to fuel injection volume. Factors like engine differences, wear, and environment cause short-term fuel trim to vary. Long-term fuel trim compensates for these long-term deviations.

Hint:

• When DTC P0171 is stored, the air fuel ratio is lean. When DTC P0172 is stored, the air fuel ratio is rich.
• If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 may be stored. The MIL then illuminates.
• When the total of short-term and long-term fuel trim values is within the malfunction threshold (and engine coolant temperature is above 75°C (167°F)), the system is functioning normally.

MONITOR DESCRIPTION

Under closed-loop fuel control, deviations in fuel injection volume from the ECM's estimate affect the long-term fuel trim compensation value. Long-term fuel trim is adjusted for persistent short-term fuel trim deviations. Deviations also affect the average fuel trim learning value. If this learning value exceeds a malfunction threshold, the ECM interprets it as a fuel system fault and stores a DTC.

Example: An average fuel trim learning value of 35% or more, or -35% or less, indicates a fuel system malfunction.

Fuel Compensation Amount Graph:

The graph shows Fuel Compensation Amount on the Y-axis and time implicitly on the X-axis. A line at 1.0 represents the stoichiometric level. P0171 (+35% Malfunction Threshold of Lean Condition) is indicated above 1.0, and P0172 (-35% Malfunction Threshold of Rich Condition) is indicated below 1.0, with thresholds at 1.35 and 0.65 respectively.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

Monitor runs whenever the following DTCs are not present:

• P0010 (Camshaft timing oil control valve assembly bank 1)
• P0011 (VVT system bank 1 - advance)
• P0012 (VVT system bank 1 - retard)
• P0016 (VVT system bank 1 - misalignment)
• P0031, P0032, P101D (Air fuel ratio sensor heater - sensor 1)
• P0102, P0103 (Mass air flow meter)
• P0107, P0108 (Manifold absolute pressure)
• P0115, P0117, P0118 (Engine coolant temperature sensor)
• P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle position sensor)
• P0125 (Insufficient coolant temperature for closed loop fuel control)
• P0335 (Crankshaft position sensor)
• P0340, P0342, P0343 (Camshaft position sensor)
• P0351, P0352, P0353, P0354 (Igniter)
• P0401 (EGR system (closed))
• P219A (Air fuel ratio sensor - imbalance)

Fuel system status: Closed-loop

Auxiliary battery voltage: 11 V or more

Conditions for enabling:

• Engine speed less than 1100 rpm
• Intake air amount per revolution 0.12 g/rev or more
• Catalyst monitor: Not executed

TYPICAL MALFUNCTION THRESHOLDS

• Purge-cut: Executing
• Either of the following conditions 1 or 2 is met:
• Average between short-term fuel trim and long-term fuel trim 35% or more (varies with engine coolant temperature)
• Average between short-term fuel trim and long-term fuel trim -35% or less (varies with engine coolant temperature)

CONFIRMATION DRIVING PATTERN

Description: The pattern involves warming up the engine, idling, and then driving at specific speeds for set durations. Engine coolant temperature must be 75°C (167°F) or higher during certain phases.

Steps:

1. Connect the Techstream to the DLC3.
2. Turn the power switch on (IG) and turn the Techstream on.
3. Clear the DTCs.
4. Turn the power switch off and wait for 30 seconds.
5. Turn the power switch on (IG) and turn the Techstream on [A].
6. Put the engine in inspection mode (maintenance mode).
7. Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher, with accessories switched off [B].
8. Idle the engine for 2 minutes or more [C].
9. Drive the vehicle at between 47 and 75 mph (75 and 120 km/h) for 5 minutes or more [D].
10. Enter menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
11. Read the pending DTC [E].

Hint:

• If a pending DTC is output, the system is malfunctioning.
• If no pending DTC is output, perform a universal trip and check for permanent DTCs.
• 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 and P2195 for wiring diagrams.

INSPECTION PROCEDURE

NOTICE: Inspect fuses for circuits related to this system before proceeding.

Hints:

• Read freeze frame data using Techstream to understand vehicle and driving conditions when a DTC was stored.
• A low air fuel ratio sensor voltage may indicate a rich mixture; check for rich running conditions.
• A high air fuel ratio sensor voltage may indicate a lean mixture; check for lean running conditions.
• Sensor 1 is closest to the engine; Sensor 2 is farthest.

PROCEDURE

1. CHECK OTHER DTCs OUTPUT (IN ADDITION TO DTC P0171 OR P0172)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Enter menus: Powertrain / Engine and ECT / Trouble Codes.
5. Read DTCs.

Hint: If DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.

2. CHECK PCV HOSE CONNECTIONS

Inspect PCV hose connections. [Link: More Info]

OK: PCV hose is connected correctly and not damaged.

NG: REPAIR OR REPLACE PCV HOSE

3. CHECK INTAKE SYSTEM

Check the intake system for vacuum leaks. [Link: More Info]

OK: No leaks in intake system.

NG: REPAIR OR REPLACE INTAKE SYSTEM

4. PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Put engine in inspection mode (maintenance mode). [Link: More Info]
5. Start the engine.
6. Warm up the engine and run at 2500 rpm for approximately 90 seconds.

Hint: During charging control, engine speed is set at idle. If accelerator pedal is not increasing speed, warm up after charging control is complete.

7. Enter menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume / Gas AF Control / AFS Voltage B1S1 and O2S B1S2.
8. Perform Control the Injection Volume operation with engine idling (use RIGHT/LEFT button to change volume).
9. Monitor AFS Voltage B1S1 and O2S B1S2 on Techstream.

Hints:

• Change injection volume between -12% to +12% in fine gradations.
• Air fuel ratio sensor has a few seconds delay; heated oxygen sensor has approx. 20 seconds delay.
• If sensor output voltage does not change (no reaction) during Active Test, the sensor may be malfunctioning.

Standard Values:

Result Interpretation:

Lean Condition: During Injection Volume Control, AFS Voltage B1S1 is consistently higher than 3.4 V, and O2S B1S2 is consistently below 0.4 V.

Rich Condition: During Injection Volume Control, AFS Voltage B1S1 is consistently below 3.1 V, and O2S B1S2 is consistently higher than 0.55 V.

Lean/Rich Condition: During Injection Volume Control of Active Test, heated oxygen sensor output voltage alternates correctly.

[Link: Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2]]

5. READ VALUE USING TECHSTREAM (COOLANT TEMP)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Enter menus: Powertrain / Engine and ECT / Data List / Primary / Coolant Temp.
5. Read Data List when engine is cold and when warmed up.

Standard value:

• Cold engine: Same as ambient air temperature.
• Warm engine: 75°C to 100°C (167°F to 212°F).

6. READ VALUE USING TECHSTREAM (MAF)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Put engine in inspection mode (maintenance mode). [Link: More Info]
5. Start the engine.
6. Enter menus: Powertrain / Engine and ECT / Data List / Primary / MAF and Coolant Temp.
7. Idle engine until Coolant Temp reaches 75°C (167°F) or higher.
8. Read MAF at 2500 rpm.

Standard MAF: Between 4.5 gm/sec and 8.5 gm/sec (shift position: P).

Hint: During charging control, engine speed is set at idle. If accelerator pedal is not increasing speed, read Data List after charging control is complete.

7. CHECK FUEL PRESSURE

Check the fuel pressure. [Link: More Info]

NG: REPAIR OR REPLACE FUEL SYSTEM

8. CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leaks.

OK: No gas leaks.

NG: REPAIR OR REPLACE EXHAUST SYSTEM

9. CHECK FOR SPARK (SPARK TEST)

Perform a spark test. [Link: More Info]

Hint: If spark test is normal, proceed. If spark plugs or ignition system malfunction, engine misfire may occur. Misfire count can be read via Techstream (Powertrain / Engine and ECT / Data List / Gas Misfire / Cylinder #1 Misfire Count to Cylinder #4 Misfire Count).

10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

Check injection and volume. [Link: More Info]

OK: GO TO STEP 15

NG: [Link: More Info]

11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

[Link: More Info]

NG: [Link: More Info]

12. CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)

[Link: More Info]

NG: REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - EFI MAIN RELAY)

13. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

[Link: More Info]

NG: REPAIR OR REPLACE HARNESS OR CONNECTOR

14. REPLACE AIR FUEL RATIO SENSOR

Replace the air fuel ratio sensor. [Link: More Info]

15. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Clear DTCs. [Link: More Info]
5. Turn power switch off and wait 30 seconds.
6. Turn power switch on (IG) and turn Techstream on.
7. Put engine in inspection mode (maintenance mode). [Link: More Info]
8. Start power and warm up.
9. Drive according to Confirmation Driving Pattern.
10. Enter menus: Powertrain / Engine and ECT / Utility / Trouble Codes / Pending.
11. Read pending DTCs.

16. PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE EGR STEP POSITION)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Put engine in inspection mode (maintenance mode). [Link: More Info]
5. Start engine and warm up until coolant temperature reaches 75°C (167°F) or more.

Hint: A/C switch and all accessory switches should be off.

6. Enter menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.
7. Confirm Throttle Idle Position is ON and check MAP value in Data List during Active Test.

NOTICE:

• Do not leave EGR valve open for 10 seconds or more during Active Test.
• Return EGR valve to step 0 when Active Test is completed.
• Do not open EGR valve 30 steps or more during Active Test.

MAP change in response to EGR step position when Throttle Idle Position is ON:

Hint: If MAP increase is small during Active Test, EGR valve assembly may be malfunctioning. Even with a malfunctioning EGR valve assembly, rough idling or MAP increase may occur, but the increase will be smaller than normal.

17. INSPECT EGR VALVE ASSEMBLY

Remove the EGR valve assembly. [Link: More Info]

Check if the EGR valve is stuck open.

OK: EGR valve is tightly closed.

NG: [Link: More Info]

18. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION)

Check connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter sub-assembly and ECM. [Link: More Info]

Hint: Repair any problems.

19. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Clear DTCs. [Link: More Info]
5. Turn power switch off and wait 30 seconds.
6. Turn power switch on (IG) and turn Techstream on.
7. Put engine in inspection mode (maintenance mode). [Link: More Info]
8. Start engine and warm it up.
9. Drive according to Confirmation Driving Pattern.
10. Enter menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
11. Read pending DTCs.

20. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY - ECM)

[Link: More Info]

NG: REPAIR OR REPLACE HARNESS OR CONNECTOR

21. REPLACE MASS AIR FLOW METER SUB-ASSEMBLY

Replace the mass air flow meter sub-assembly. [Link: More Info]

Hint: If inspection in step 6 indicated no problem, proceed without replacing the mass air flow meter sub-assembly.

22. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

1. Connect Techstream to DLC3.
2. Turn power switch on (IG).
3. Turn Techstream on.
4. Clear DTC. [Link: More Info]
5. Turn power switch off and wait 30 seconds.
6. Turn power switch on (IG) and turn Techstream on.
7. Put engine in inspection mode (maintenance mode). [Link: More Info]
8. Start engine and warm it up.
9. Drive according to Confirmation Driving Pattern.
10. Enter menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
11. Read pending DTCs.