P0172
2UZ-FE 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 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 (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 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 sets a DTC.
HINT:
- When DTC P0171 or P0174 is recorded, the actual air fuel ratio is on the LEAN side. When DTC P0172 or P0175 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 or P0174 may be recorded. The MIL is then illuminated.
- If the total of the short-term fuel trim value and long-term fuel trim value is within +-35 % (and ECT is more than 75°C (167°F)), the system is functioning normally.
MONITOR DESCRIPTION
Under closed-loop fuel control, fuel injection amounts that deviate from the ECM's estimated fuel amount will cause a change in the long-term fuel trim compensation value. Long-term fuel trim value is adjusted when persistent deviations in the short-term fuel trim's value are present. Also, the smoothed fuel trim learning value is adjusted when deviations from the ECM's simulated fuel injection value are present. 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 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 more than +35 % or less than -35 %, the ECM interprets this as a fuel system malfunction.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
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 the Techstream.
1 Connect the Techstream to the DLC3.
2 Start the engine and turn the tester ON.
3 Warm up the engine at an 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 voltage outputs of the A/F and HO2 sensors (AFS B1S1 and O2S B1S2 or AFS 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 in the fuel injection volume.
Standard voltage:
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 B1 S1 and O2S B1 S2 or AFS B2 S1 and O2S B2 S2.
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 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 lean air fuel mixture. Check for conditions that would cause the engine to run lean.
PROCEDURE
1. CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174, P0175)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON and turn the tester ON.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(d) Read the DTCs.
Result:
HINT: If any DTCs other than P0171, P0172, P0174 and P0175 are output, troubleshoot those DTCs first.
B -- GO TO DTC CHART
A -- Continue to next step.
2. CHECK CONNECTION OF 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 leaks.
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 the 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 outputs of A/F and HO2 sensors (AFS B1S1 and O2S B1S2 or AFS 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 in the fuel injection volume.
Standard voltage:
Result:
Lean: During Control the Injection Volume for A/F Sensor, the A/F sensor output voltage (AFS) is consistently more than 3.35 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 3.0 V, and the O2S is consistently more 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 ON 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 value when the engine is cold and warmed up.
Standard:
ECT when the engine is cold: Same as ambient temperature
ECT when the engine is warmed up: 75 to 95°C (167 to 203°F)
NG -- REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK -- Continue to next step.
6. INSPECT MASS AIR FLOW METER
(a) Inspect the output voltage.
(1) Apply battery voltage across terminals 3 (+B) and 4 (E2G).
(2) Connect the positive (+) tester probe to terminal 5 (VG), and the negative (-) tester probe to terminal 4 (E2G).
(3) Blow air into the MAF meter.
Standard condition:
Voltage fluctuates
(b) Inspect the resistance.
(1) )Using an ohmmeter, measure the resistance between terminals 2 (THA) and 1 (E2).
Standard resistance:
12.5 to 16.9 kOhms at -20°C (-4°F)
2.19 to 2.67 kOhms at 20°C (68°F)
0.50 to 0.68 kOhms at 60°C (140°F)
(c) If using a intelligent tester:
Inspect the mass air flow meter.
(1) Connect the intelligent tester to the DLC3.
(2) Turn the ignition switch to the ON position.
(3) Blow air into the MAF meter.
Standard condition:
Air flow value of the CURRENT DATA changes
(d) If not using a intelligent tester:
Inspect the mass air flow meter.
(1) Turn the ignition switch to the ON position.
(2) Connect the positive tester probe of the voltmeter to terminal VG of the ECM and the negative tester probe of the voltmeter to terminal E2G of the ECM.
(3) Blow air into the air flow meter.
Standard condition:
Voltage fluctuates
NG -- REPLACE MASS AIR FLOW METER
OK -- Continue to next step.
7. CHECK FUEL PRESSURE
(a) Check the fuel pressure Testing and Inspection.
NG -- REPAIR OR REPLACE FUEL SYSTEM
OK -- Continue to next step.
8. CHECK FOR EXHAUST GAS LEAK
OK:
No gas leakage.
NG -- REPAIR OR REPLACE EXHAUST SYSTEM
OK -- Continue to next step.
9. CHECK FOR SPARK AND IGNITION
(a) Check for spark and ignition P0300.
HINT: If the spark plugs or ignition system malfunction, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Misfire / Cylinder #1 Misfire Count (to Cylinder #8 Misfire Count).
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
10. INSPECT FUEL INJECTOR (INJECTION AND VOLUME)
(a) Inspect the fuel injector Testing and Inspection.
HINT: If the injectors are malfunctioning, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Misfire / Cylinder #1 Misfire Count (to Cylinder #8 Misfire Count).
NG -- REPLACE FUEL INJECTOR
OK -- Continue to next step.
11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the A41 or A42 Air Fuel Ratio (A/F) sensor connector.
(b) Measure the resistance of the A/F sensor.
Standard resistance:
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.
12. INSPECT A/F RELAY
(a) Remove the A/F relay from the engine room R/B.
(b) Measure the resistance of the A/F relay.
Standard resistance:
NG -- REPLACE A/F RELAY
OK -- Continue to next step.
13. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
(a) Disconnect the A41 or A42 A/F sensor connector.
(b) Turn the ignition switch ON.
(c) Measure the voltage between the +B terminal of the A/F sensor connector and body ground.
Standard voltage:
(d) Turn the ignition switch OFF.
(e) Disconnect the E6 ECM connector.
(f) Check the resistance.
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.
14. REPLACE AIR FUEL RATIO SENSOR
NEXT -- Continue to next step.
15. PERFORM CONFIRMATION DRIVING PATTERN
(a) Connect the Techstream to the DLC3 [A].
(b) Turn the ignition switch ON and turn the tester ON [B].
(c) Clear DTCs DTC Check / Clear [C].
(d) Switch the ECM from normal mode to check mode using the tester Check Mode Procedure [D].
(e) Start the engine and warm it up with all the accessories switched OFF [E].
(f) Drive the vehicle at between 38 and 75 mph (60 and 120 km/h) and at an engine speed of between 1400 rpm and 3200 rpm for 3 to 5 minutes [F].
HINT: If the system is still malfunctioning, the MIL will be illuminated during step [F].
NOTE:
If the conditions in this test are not strictly followed, no malfunction will be detected.
NEXT -- Continue to next step.
16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)
(a) On the Techstream, enter the following menu: Powertrain / Engine and ECT / Trouble Codes.
(b) Read the DTCs.
Result:
B -- READ VALUE USING TECHSTREAM (COOLANT TEMP)
A -- END