P0172
3UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0171,P0172,P0174,P0175: 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 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 the stoichiometric air-fuel ratio. The signal from the heated oxygen 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 short-term fuel trim varies from the central value due to individual engine differences, wear over time and changes in the operating environment. The long-term fuel trim, which controls overall fuel compensation, steadies long-term deviations of the short-term fuel trim from the central value.
If both the short-term fuel trim and the long-term fuel trim are lean or rich beyond a certain value, the ECM determines this to be a malfunction, 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 the malfunction threshold (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 a 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 smoothed fuel trim learning value is above 35% or below -35%. The ECM interprets this as a fault in the fuel system.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
CONFIRMATION DRIVING PATTERN
- Connect the Techstream to the DLC3.
- Turn the ignition switch to ON and turn the Techstream on.
- Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
- Turn the ignition switch off and wait for at least 30 seconds.
- Turn the ignition switch to ON and turn the Techstream on [A].
- 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].
- With the engine warmed up, idle the engine for 2 minutes or more [C].
- Drive the vehicle at between 60 and 120 km/h (38 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.
- Enter the following menus: Powertrain / Engine / Trouble Codes [E].
- 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.
- Enter the following menus: Powertrain / Engine / Utility / All Readiness.
- Input the DTC: P0171, P0172, P0174 or P0175.
- Check the DTC judgment result.
HINT
If the judgment result shows INCOMPLETE or UNKNOWN, perform steps [C] through [E] again.
- If no pending DTC is output, perform a universal trip and check for permanent DTCs Reading and Clearing Diagnostic Trouble Codes.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
WIRING DIAGRAM
INSEPCTION PROCEDURE
HINT
It is possible that the malfunctioning area can be found using the Active Test Control the Injection Volume for A/F Sensor operation. The Active Test can determine if the heated oxygen sensor or other potential trouble areas are malfunctioning or not.
The injection volume can be switched to -12.5% (decrease) or +25% (increase) by the Active Test.
The Active Test procedure enables a technician to check and graph the output voltage of the heated oxygen sensors.
- Procedure:
- Connect the Techstream to the DLC3.
- Turn the ignition switch to ON.
- Warm up the engine by running the engine at 2500 rpm for approximately 90 seconds.
- Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
- Perform the Active Test while the engine is idling.
Standard:
The heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:
+25% -> Rich output: More than 0.55 V
-12.5% -> Lean output: Less than 0.4 V
NOTICE:
The heated oxygen sensor (sensor 1) output has a few seconds of delay and the heated oxygen sensor (sensor 2) output has a maximum of 20 seconds of delay.
If the vehicle is short on fuel, the air-fuel ratio becomes lean and the DTCs will be recorded.
NOTICE:
Inspect the fuses for circuits related to this system before performing the following inspection procedure.
HINT
- Read freeze frame data using the Techstream. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, 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 high heated oxygen sensor (sensor 1) voltage (0.55 V or more) indicates a rich air-fuel ratio.
- A low heated oxygen sensor (sensor 1) voltage (0.4 V or less) indicates a lean air-fuel ratio.
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 to ON and turn the Techstream on.
(c) Enter the following menus: Powertrain / Engine / Trouble Codes.
(d) Read the DTCs.
Result:
B -- GO TO DTC CHART Diagnostic Trouble Code Descriptions
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.
NG -- REPAIR OR REPLACE AIR INDUCTION SYSTEM
OK -- Continue to next step.
4. PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL)
(a) Perform the Active Test Control the Injection Volume for A/F Sensor with the Techstream and check the heated oxygen sensor status.
Standard Voltage:
Heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:
+25% -> Rich output: More than 0.55 V
-12.5% -> Lean output: Less than 0.4 V
HINT
L: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.4 V or less (lean).
R: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.55 V or more (rich).
D -- INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE (SENSOR 1))
C -- INSPECT FUEL INJECTOR
B -- CHECK FOR EXHAUST GAS LEAKAGE
A -- Continue to next step.
5. READ VALUE USING TECHSTREAM (COOLANT TEMP)
(a) Connect the Techstream to the DLC3.
(b) Enter the following menus: Powertrain / Engine / Data List / Coolant Temp.
(c) 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) Read the values using the Techstream (MAF).
NOTICE:
- Turn the ignition switch to OFF.
- Perform the inspection with the vehicle indoors and on a level surface.
- Perform the inspection of the mass air flow meter while it is installed in the air cleaner case (installed on the vehicle).
- During the test, do not use the exhaust air duct to perform suction on the exhaust pipe.
(1) Connect the Techstream to the DLC3.
(2) Turn the ignition switch to ON (do not start the engine).
(3) Turn the Techstream on.
(4) Enter the following menus: Powertrain / Engine / Data List / MAF.
(5) Wait for 30 seconds, and read the values on the Techstream.
Standard:
Less than 0.51 g/sec
(b) Inspect the mass air flow meter.
(1) Remove the mass air flow meter Service and Repair.
(2) Using a work light, check that the platinum filament (heater portion) in the mass air flow meter has no foreign matter attached.
OK:
No foreign matter attached.
NG -- REPLACE MASS AIR FLOW METER Service and Repair
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 LEAKAGE
OK:
No gas leak.
NG -- REPAIR OR REPLACE EXHAUST SYSTEM
OK -- Continue to next step.
9. CHECK FOR SPARK AND IGNITION
HINT
- Refer to the ignition system inspection procedure Testing and Inspection.
- 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 / Data List / Cylinder #1 Misfire Count to #8.
NG -- REPAIR OR REPLACE IGNITION SYSTEM
OK -- Continue to next step.
10. INSPECT FUEL INJECTOR
HINT
- Refer to the fuel injector inspection procedure Testing and Inspection.
- If the injectors are malfunctioning, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine / Data List / Cylinder #1 Misfire Count to #8.
NG -- REPLACE FUEL INJECTOR
OK -- PERFORM CONFIRMATION DRIVING PATTERN
11. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE (SENSOR 1)) P0031
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
12. CHECK TERMINAL VOLTAGE (POWER SOURCE OF HEATED OXYGEN SENSOR (SENSOR 1))
(a) Disconnect the heated oxygen sensor connectors.
(b) Turn the ignition switch to ON.
(c) Measure the voltage according to the value(s) in the table below.
Standard Voltage:
NG -- CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - EFI RELAY)
OK -- Continue to next step.
13. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR (SENSOR 1) - ECM) P0031
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
14. REPLACE HEATED OXYGEN SENSOR
(a) Replace the heated oxygen sensor (sensor 1).
NEXT -- Continue to next step.
15. PERFORM CONFIRMATION DRIVING PATTERN
(a) Refer to the confirmation driving pattern for P0171, P0172, P0173 and P0174.
NEXT -- Continue to next step.
16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0173 OR P0174)
(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 / Trouble Code / Pending.
(e) Read the Pending DTCs.
Result:
B -- REPLACE ECM Service and Repair
A -- END
17. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - EFI RELAY) P0031
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- CHECK ECM POWER SOURCE CIRCUIT ECM Power Source Circuit