P0172

1NZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0171: System Too Lean (Fuel Trim)

DTC P0171 - System Too Lean (Fuel Trim)

DTC P0172 - System Too Rich (Bank 1)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and the long-term fuel trim.
The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at stoichiometric air-fuel ratio. The signal from the A/F sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the stoichiometric air-fuel ratio. This variance triggers a reduction in the fuel volume if the air-fuel ratio is RICH, and an increase in the fuel volume if it is LEAN.
The long-term fuel trim is the overall fuel compensation carried out in long-term to compensate for a continual deviation of the short-term fuel trim from the central value, due to individual engine differences, wear overtime and changes in the operating environment.
If both the short-term fuel trim and the long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL is illuminated and a DTC is set.





HINT:
- When DTC P0171 is recorded, the actual air-fuel ratio is on the LEAN side. When DTC P0172 is recorded, 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 recorded. The MIL then illuminates.
- If the total of the short-term fuel trim value and long-term fuel trim value is between +33% and -30% (engine coolant temperature is more than 75°C (167°F)), the system is functioning normally.

MONITOR DESCRIPTION





Under closed-loop fuel control, fuel injection amount that deviates from the ECM's estimated fuel amount will cause a change in the long-term fuel trim compensation value. This long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. And the deviation from the simulated fuel injection amount by the ECM affects a smoothed fuel trim learning value. The smoothed fuel trim learning value is the combination of smoothed short-term fuel trim (fuel feedback compensation value) and smoothed long-term fuel trim (learning value of the air-fuel ratio). When the smoothed fuel trim learning value exceeds the DTC threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.
Example:
The smoothed fuel trim leaning value is more than +33% or less than -30%.
The ECM interprets this as a failure in the fuel system.
DTC P0171 indicates that the air-fuel mixture is extremely LEAN, and P0172 indicates extremely RICH.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





WIRING DIAGRAM





INSPECTION PROCEDURE
HINT: Malfunctioning areas can be found by performing the Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor operation. The Control the Injection Volume for A/F Sensor operation can determine if the A/F sensor, heated oxygen sensor or other potential trouble area are malfunctioning or not.

(a) Perform the Control the Injection Volume for A/F Sensor operation.
HINT: The Control the Injection Volume for A/F Sensor operation lowers the injection volume 12.5% or increases the injection volume 25%.

(1) Connect Techstream to the DLC3.
(2) Turn the power switch ON (IG).
(3) Put the engine in inspection mode Service Precautions.
(4) Warm up the engine by running the engine at 2,500 rpm, depressing the accelerator pedal more than 60% for approximately 90 seconds.
(5) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
(6) Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idle condition (press the right or left button).
Result:
A/F sensor reacts in accordance with increase and decrease of injection volume:
+25% = rich output: Less than 3.1 V
-12.5% = lean output: More than 3.4 V
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume:
+25% = rich output: More than 0.55 V
-12.5% = lean output: Less than 0.4 V
NOTE: The A/F sensor output has a few seconds of delay and the heated oxygen sensor output has about 20 seconds of delay at maximum.





The following Control the Injection Volume for A/F Sensor procedure enables the technician to check and graph the voltage output of both A/F sensor and heated oxygen sensor.
To display the graph, enter 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.
- A high A/F sensor voltage could be caused by a RICH air-fuel mixture. Check the conditions that would cause the engine to run with the RICH air-fuel mixture.
- A low A/F sensor voltage could be caused by a LEAN air-fuel mixture. Check the conditions that would cause the engine to run with the LEAN air-fuel mixture.

PROCEDURE

1. CHECK AIR INDUCTION SYSTEM
(a) Check for vacuum leaks in the air induction system.
OK:
No vacuum leakage.
NG -- REPAIR OR REPLACE AIR INDUCTION SYSTEM
OK -- Continue to next step.

2. CHECK CONNECTION OF PCV HOSE
OK:
PCV hose is connected correctly and PCV hose is not damaged.
NG -- REPAIR OR REPLACE PCV HOSE
OK -- Continue to next step.

3. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
OK:
Injection volume: 36 to 46 cm3 (2.1 to 2.8 cu in.) per 15 seconds.
NG -- REPLACE FUEL INJECTOR ASSEMBLY
OK -- Continue to next step.

4. INSPECT MASS AIR FLOW METER
(a) Connect Techstream to the DLC3.
(b) Turn the power switch on (ACC).
(c) Turn the power switch on (do not start the engine).
(d) Turn the Techstream ON.
(e) Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.
(f) Wait 30 seconds, and read the values on the Techstream.
Result:
Less than 0.07 g/sec.
NG -- REPLACE MASS AIR FLOW METER
OK -- Continue to next step.

5. INSPECT ENGINE COOLANT TEMPERATURE SENSOR (RESISTANCE)




(a) Remove the engine coolant temperature sensor.
(b) Measure the resistance between the terminals of the engine coolant temperature sensor.
Standard resistance:





NOTE: When checking the engine coolant temperature sensor in water, be careful not to allow water to contact the terminals. After checking, dry the sensor.
HINT: Alternate procedure: Connect an ohmmeter to the installed engine coolant temperature sensor and read the resistance. Use an infrared thermometer to measure the engine temperature in the immediate vicinity of the sensor. Compare these values to the resistance/temperature graph. Change the engine temperature (warm up or allow to cool down) and repeat the test.
(c) Reinstall the engine coolant temperature sensor.
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK -- Continue to next step.

6. CHECK SPARK AND IGNITION
OK:
Sparks occur.
NG -- REPAIR OR REPLACE IGNITION SYSTEM COMPONENTS
OK -- Continue to next step.

7. CHECK FUEL PRESSURE
OK:
Fuel pressure: 304 to 343 kPa (3.1 to 3.5 kgf/cm2, 44 to 50 psi)
NG -- REPAIR OR REPLACE FUEL SYSTEM
OK -- Continue to next step.

8. INSPECT FOR EXHAUST GAS LEAK
OK:
No gas leakage.
NG -- REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT
OK -- Continue to next step.

9. READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF AIR FUEL RATIO SENSOR [BANK 1 SENSOR 1])
(a) Connect Techstream to the DLC 3.
(b) Put the engine in inspection mode Service Precautions.
(c) Warm up the A/F sensors (bank 1 sensor 1) by running the engine at 2,500 rpm with the accelerator pedal depressed more than 60 % for approximately 90 seconds.
(d) Read the A/F sensor voltage output on Techstream.
(e) Enter the following menus: Powertrain / Engine and ECT / Data List.
(f) Select "AFS Voltage B1 S1/Engine Speed" and press button "YES".
(g) Monitor the A/F sensor voltage carefully.
(h) Check the A/F sensor voltage output under the following conditions:
(1) Put the engine in inspection mode and allow the engine to idle for 30 seconds.
(2) Put the engine in inspection mode and run the engine at 2,500 rpm with the accelerator pedal depressed more than 60% (where engine RPM is not suddenly changed).
(3) Deactivate the inspection mode and drive the vehicle with the shift position "B".
(4) Accelerate the vehicle to 70 km/h (44 mph) and quickly release the accelerator pedal so that the throttle valve is fully closed.
CAUTION:
- Strictly observe posted speed limits, traffic laws, and road conditions when performing these drive patterns.
- Do not drive the vehicle without deactivating inspection mode, otherwise damaging the transaxle may result.

OK:
Conditions (1) and (2)
Voltage changes in the vicinity of 3.3 V (between approximately 3.1 and 3.5 V) as shown in the illustration.
Condition (4)
A/F sensor voltage increases to 3.8 V or more during engine deceleration (when fuel cut) as shown in the illustration.




HINT:
- Whenever the output voltage of the A/F sensor remains at approximately 3.3 V (see diagram Malfunction Condition) under any condition as well as the above conditions, the A/F sensor may have an open-circuit. (This will also happen when the A/F sensor heater has an open-circuit.)
- Whenever the output voltage of the A/F sensor remains at a certain value of approximately 3.8 V or more, or 2.8 V or less (see diagram Malfunction Condition) under any condition as well as the above conditions, the A/F sensor may have a short-circuit.
- The ECM will stop fuel injection (fuel cut) during engine deceleration. This will cause a LEAN condition and should result in a momentary increase in A/F sensor voltage output.
- The ECM must establish a closed throttle position learned value to perform fuel cut. If the battery terminal was reconnected, the vehicle must be driven over 10 mph to allow the ECM to learn the closed throttle position.
- When the vehicle is driven:
The output voltage of the A/F sensor may be below 2.8 V during fuel enrichment. For the vehicle, this translates to a sudden increase in speed with the accelerator pedal fully depressed when trying to overtake another vehicle. The A/F sensor is functioning normally.
- The A/F sensor is a current output element, and therefore the current is converted into voltage inside the ECM. If measuring the voltage at the connectors of the A/F sensor or ECM, you will observe a constant voltage.

OK -- PERFORM CONFIRMATION DRIVING PATTERN
NG -- Continue to next step.

10. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)




(a) Disconnect the A5 A/F sensor connector.
(b) Measure the resistance between the terminals of the A/F sensor.
Standard resistance:





(c) Reconnect the A/F sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.

11. INSPECT INTEGRATION RELAY (EFI M RELAY)




(a) Remove the integration relay from the engine room relay block.
(b) Inspect the EFI M relay.
Standard resistance:





(c) Reinstall the integration relay.
NG -- REPLACE INTEGRATION RELAY
OK -- Continue to next step.

12. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
(a) Disconnect the A5 A/F sensor connector.








(b) Disconnect the E5 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 A/F sensor connector.
(e) Reconnect the ECM connector.





NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.

13. REPLACE AIR FUEL RATIO SENSOR
(a) Replace the air fuel ratio sensor Removal.
NEXT -- Continue to next step.

14. PERFORM CONFIRMATION DRIVING PATTERN




(a) Clear the DTCs DTC Check / Clear.
(b) Connect Techstream to the DLC3.
(c) Switch the ECM from normal mode to check mode using Techstream Check Mode Procedure.
(d) Put the engine in inspection mode, and start the engine and warm it up with all the accessory switches OFF.
(e) Deactivate inspection mode and drive the vehicle at 44 to 75 mph (70 to 120 km/h) and engine speed of 1,100 to 3,200 rpm for 5 to 10 minutes.
HINT: If a malfunction exists, the MIL will be illuminated during step (e).
NOTICE:
- If the conditions in this test are not strictly followed, no malfunction will be detected. If you do not have Techstream, turn the power switch OFF after performing steps (d) and (e), then perform step (e) again.
- Do not drive the vehicle without deactivating inspection mode, otherwise damaging the transaxle may result.

NEXT -- Continue to next step.

15. READ OUTPUT DTCS (SEE IF DTC P0171 AND/OR P0172 ARE OUTPUT AGAIN)
(a) Connect Techstream to the DLC3.
(b) Turn the power switch ON (IG).
(c) Turn Techstream ON.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code.
(e) Read the DTCs using Techstream.
Result:






B -- REPLACE ECM AND PERFORM CONFIRMATION DRIVING PATTERN
A -- Continue to next step.

16. CONFIRM IF VEHICLE HAS RUN OUT OF FUEL IN PAST
NO -- CHECK FOR INTERMITTENT PROBLEMS
YES -- DTCS ARE CAUSED BY RUNNING OUT OF FUEL (DTCS P0171 AND/OR P0172)
17. PERFORM CONFIRMATION DRIVING PATTERN
HINT: Clear all DTCs prior to performing the confirmation driving pattern.

NEXT -- Continue to next step.

18. READ OUTPUT DTCS (SEE IF DTC P0171 AND/OR P0172 ARE OUTPUT AGAIN)
(a) Connect Techstream to the DLC3.
(b) Turn the power switch ON (IG).
(c) Turn Techstream ON.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code.
(e) Read the DTCs using Techstream.
Result:






B -- CONFIRM IF VEHICLE HAS RUN OUT OF FUEL IN PAST
A -- Continue to next step.

19. REPLACE AIR FUEL RATIO SENSOR
(a) Replace the air fuel ratio sensor Removal.
NEXT -- Continue to next step.

20. PERFORM CONFIRMATION DRIVING PATTERN
HINT: Clear all DTCs prior to performing the confirmation driving pattern.

NEXT -- Continue to next step.

21. READ OUTPUT DTCS (SEE IF DTC P0171 AND/OR P0172 ARE OUTPUT AGAIN)
(a) Connect Techstream to the DLC3.
(b) Turn the power switch ON (IG).
(c) Turn Techstream ON.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Code.
(e) Read the DTCs using Techstream.
Result:






B -- REPLACE ECM AND PERFORM CONFIRMATION DRIVING PATTERN
A -- Continue to next step.

22. CONFIRM IF VEHICLE HAS RUN OUT OF FUEL IN PAST
OK:
The vehicle has run out of fuel in the past.
NO -- CHECK FOR INTERMITTENT PROBLEMS
YES -- DTCS ARE CAUSED BY RUNNING OUT OF FUEL