CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)
PERFORM ACTIVE TEST BY INTELLIGENT TESTER (A/F CONTROL)
READ VALUE OF ENGINE COOLANT TEMPERATURE SENSOR (COOLANT TEMP)
READ VALUE OF INTAKE AIR FLOW METER (MAF)
CHECK FUEL PRESSURE (LOW PRESSURE SIDE)
CHECK FUEL PRESSURE (HIGH PRESSURE SIDE)
INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
PERFORM CONFIRMATION DRIVING PATTERN
CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)
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.
| DTC No. | DTC Detection Condition | Trouble Area |
| P0171 P0174 |
With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic) |
|
| P0172 P0175 |
With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic) |
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HINT:
- When DTC P0171 or P0174 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is set, 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 set. 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 more than 75°C [167°F]), the system is functioning normally.
Wiring diagram
Refer to DTC P2195
Inspection procedure
HINT:
Intelligent tester only:
Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE TEST. The A/F CONTROL 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 A/F CONTROL operation using an intelligent tester.
- Connect the intelligent tester to the DLC3.
- Start the engine and turn the tester ON.
- Warm up the engine at engine speed of 2,500 rpm for approximately 90 seconds.
- On the tester, enter the following menus: Power train / Engine / Active Test / Control the Injection Volume for A/F Sensor.
- Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume.)
- Monitor the output voltages of the A/F and HO2 sensors (AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) displayed on the tester.
HINT:
- The A/F CONTROL operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
- Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
| Tester Display (Sensor) |
Injection Volume | Status | Voltage |
| AFS B1S1 or AFS B2S1 (A/F) |
+25 % | Rich | Less than 3.0 |
| AFS B1S1 or AFS B2S1 (A/F) |
-12.5 % | Lean | More than 3.35 |
| O2S B1S2 or O2S B2S2 (HO2) |
+25 % | Rich | More than 0.55 |
| O2S B1S2 or O2S B2S2 (HO2) |
-12.5 % | Lean | Less than 0.4 |
NOTICE:
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.
| Case | A/F Sensor (Sensor 1) Output Voltage |
HO2 Sensor (Sensor 2) Output Voltage |
Main Suspected Trouble Area | ||
| 1 | Injection Volume +25 % -12.5 % |
 |
Injection Volume +25 % -12.5 % |
|
- |
| Output Voltage More than 3.35 V Less than 3.0 V |
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Output Voltage More than 0.55 V Less than 0.4 V |
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| 2 | Injection Volume +25 % -12.5 % |
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Injection Volume +25 % -12.5 % |
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| Output Voltage Almost no reaction |
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Output Voltage More than 0.55 V Less than 0.4 V |
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| 3 | Injection Volume +25 % -12.5 % |
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Injection Volume +25 % -12.5 % |
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| Output Voltage More than 3.35 V Less than 3.0 V |
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Output Voltage Almost no reaction |
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| 4 | Injection volume +25 % -12.5 % |
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Injection Volume +25 % -12.5 % |
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| Output Voltage Almost no reaction |
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Output Voltage Almost no reaction |
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- Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
- The following A/F Control procedure enables the technician to check and graph the voltage output of both the heated oxygen sensors. To display the graph, select the following menu items on the tester: View / Line Graph.
HINT:
- Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are 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 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 rich air-fuel mixture. Check for conditions that would cause the engine to run lean.
| 1.CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175) |
-
Connect the intelligent tester to the DLC3.
-
Turn the engine switch on (IG) and turn the tester ON.
-
Enter the following menus: Power train / Engine / DTC.
-
Read DTCs.
Result:
| Display (DTC output) | Proceed to |
| P0171, P0172, P0174 or P0175 | A |
| P0171, P0172, P0174 or P0175 and other DTCs | B |
HINT:
If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.
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| A | |
| 2.CHECK PCV HOSE |
OK:
PCV hose is connected correctly and is not damaged.
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| OK | |
| 3.CHECK AIR INDUCTION SYSTEM |
-
Check the air induction system for vacuum leakage.
OK:
No leakage from air induction system.
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| OK | |
| 4.PERFORM ACTIVE TEST BY INTELLIGENT TESTER (A/F CONTROL) |
-
Connect the intelligent tester to the DLC3.
-
Start the engine and turn the tester ON.
-
Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
-
On the tester, enter the following menus: Power train / Engine / Active Test / Control the Injection Volume for A/F Sensor.
-
Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
-
Monitor the outputs voltages of A/F and HO2 sensors (AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) displayed on the tester.
HINT:
- The A/F CONTROL operation lowers the fuel injection volume by 12.5 % or increases the injection volume by 25 %.
- Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
| Tester Display (Sensor) | Injection Volume | Status | Voltage |
| AFS B1S1 or AFS B2S1 (A/F) |
+25% | Rich | Less than 3.0 |
| AFS B1S1 or AFS B2S1 (A/F) |
-12.5% | Lean | More than 3.35 |
| O2S B1S2 or O2S B2S2 (HO2) |
+25% | Rich | More than 0.55 |
| O2S B1S2 or O2S B2S2 (HO2) |
-12.5% | Lean | Less than 0.4 |
Result:
| Status AFS B1S1 or AFS B2S1 |
Status O2S B1S2 or O2S B2S2 |
A/F Condition and A/F Sensor Condition |
Misfire | Suspected Trouble Area | Proceed to |
| Lean/Rich | Lean/Rich | Normal | - | - | C |
| Lean | Lean | Actual air-fuel ratio lean | May occur |
|
A |
| Rich | Rich | Actual air-fuel ratio rich | - |
|
A |
| Lean | Lean/Rich | A/F sensor malfunction | - |
|
B |
| Rich | Lean/Rich | A/F sensor malfunction | - |
|
B |
- Lean:
- During A/F CONTROL, 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 A/F CONTROL, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.
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| A | |
| 5.READ VALUE OF ENGINE COOLANT TEMPERATURE SENSOR (COOLANT TEMP) |
-
Connect the intelligent tester to the DLC3.
-
Turn the engine switch on (IG) and turn the tester ON.
-
Enter the following menus: Power train / Engine / Data List / Coolant Temp.
-
Read the 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 and 95°C (167 and 203°F)
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| OK | |
| 6.READ VALUE OF INTAKE AIR FLOW METER (MAF) |
-
Connect the intelligent tester to the DLC3.
-
Turn the engine switch on (IG) and turn the tester ON.
-
Enter the following menus: Power train / Engine / Data List / MAF and Coolant Temp.
-
Allow the engine to idle until the COOLANT TEMP reaches 75°C (167°F) or more.
-
Read the MAF with the engine in an idling condition and at an engine speed of 2,500 rpm.
Standard:
MAF while engine idling:
Between 2.1 g/s and 3.1 g/s (shift position: N, A/C: OFF).
MAF at an engine speed of 2,500 rpm:
Between 7.8 g/s and 11.4 g/s (shift position: N, A/C: OFF).
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| OK | |
| 7.CHECK FUEL PRESSURE (LOW PRESSURE SIDE) |
-
Check the fuel pressure (low pressure side).
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| OK | |
| 8.CHECK FUEL PRESSURE SENSOR |
-
Connect the intelligent tester to the DLC3.
-
Turn the engine switch on (IG) and turn the tester ON.
-
Start the engine.
-
Enter the following menus: Power train / Engine / Data List / Fuel Press.
-
While revving the engine, check that the fuel pressure fluctuates.
OK:
Fuel pressure fluctuates.
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| OK | |
| 9.CHECK FUEL PRESSURE (HIGH PRESSURE SIDE) |
-
Check the fuel pressure (high pressure side).
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| OK | |
| 10.CHECK FOR EXHAUST GAS LEAKAGE |
OK:
No gas leakage.
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| OK | |
| 11.CHECK FOR SPARK AND IGNITION |
HINT:
If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using an intelligent tester. Enter the following menus: Power train / Engine / Data List / Cylinder #1 (to #6) Misfire Rate.
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| OK | |
| 12.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) |
-
Disconnect the E42 or E38 A/F sensor connector.
Measure the resistance of the A/F sensor connector.
Standard resistance (Bank 1 sensor 1):
| Tester Connection | Condition | Specified Condition |
| HA1A (1) - +B (2) | 20°C (68°F) | 1.8 ? to 3.4 ? |
| HA1A (1) - A1A- (4) | - | 10 k? or higher |
Standard resistance (Bank 2 sensor 1):
| Tester Connection | Condition | Specified Condition |
| HA2A (1) - +B (2) | 20°C (68°F) | 1.8 ? to 3.4 ? |
| HA2A (1) - A2A- (4) | - | 10 k? or higher |
-
Reconnect the A/F sensor connector.
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| OK | |
| 13.INSPECT A/F HTR RELAY |
-
Remove the A/F HTR relay from the engine room J/B and R/B No. 2.
-
Measure resistance of the A/F HTR relay.
Standard resistance:
| Tester Connection | Specified Condition |
| 3 - 5 | 10 k? or higher |
| 3 - 5 | Below 1 ? (when battery voltage applied to terminals 1 and 2) |
-
Reinstall the A/F HTR relay.
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| OK | |
| 14.CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM) |
-
Disconnect the E42 and E38 A/F sensor connector.
-
Turn the engine switch on (IG).
-
Measure the voltage between the +B terminal of the A/F sensor connector and body ground.
Standard voltage:
| Tester Connection | Specified Condition |
| +B (E42-2) - Body ground | 9 to 14 V |
| +B (E38-2) - Body ground | 9 to 14 V |
-
Turn the engine switch off.
-
Disconnect the E6 ECM connector.
-
Measure the resistance of the wire harness side connector.
Standard resistance (Check for open):
| Tester Connection | Specified Condition |
| HA1A (E42-1) - HA1A (E6-6) | Below 1 ? |
| A1A+ (E42-3) - A1A+ (E6-18) | Below 1 ? |
| A1A- (E42-4) - A1A- (E6-17) | Below 1 ? |
| HA2A (E38-1) - HA2A (E6-4) | Below 1 ? |
| A2A+ (E38-3) - A2A+ (E6-28) | Below 1 ? |
| A2A- (E38-4) - A2A- (E6-27) | Below 1 ? |
Standard resistance (Check for short):
| Tester Connection | Specified Condition |
| HA1A (E42-1) or HA1A (E6-6) - Body ground | 10 k? or higher |
| A1A+ (E42-3) or A1A+ (E6-18) - Body ground | 10 k? or higher |
| A1A- (E42-4) or A1A- (E6-17) - Body ground | 10 k? or higher |
| HA2A (E38-1) or HA2A (E6-4) - Body ground | 10 k? or higher |
| A2A+ (E38-3) or A2A+ (E6-28) - Body ground | 10 k? or higher |
| A2A- (E38-4) or A2A- (E6-27) - Body ground | 10 k? or higher |
-
Reconnect the ECM connector.
-
Reconnect the A/F sensor connector.
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| OK | |
| 15.REPLACE AIR FUEL RATIO SENSOR |
| NEXT | |
| 16.PERFORM CONFIRMATION DRIVING PATTERN |
-
Connect the intelligent tester to the DLC3 (Procedure "A").
-
Turn the engine switch on (IG) and turn the tester ON (Procedure "B").
-
Clear DTCs (Procedure "C").
-
Switch the ECM from normal mode to check mode using the tester (Procedure "D").
-
Start the engine and warm it up with all the accessories switched OFF (Procedure "E").
-
Drive the vehicle at between 60 km/h and 120 km/h (38 mph and 75 mph) and at an engine speed of between 1,400 rpm and 3,200 rpm for 3 to 5 minutes (Procedure "F").
HINT:
If the system is still malfunctioning, the MIL will be illuminated during step (f).
NOTICE:
If the conditions in this test are not strictly followed, no malfunction will be detected.
| NEXT | |
| 17.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175) |
-
On the intelligent tester, enter the following menus: Power train / Engine / DTC.
-
Read DTCS.
Result:
| Display (DTC output) | Proceed to |
| No output | A |
| P0171, P0172, P0174 or P0175 | B |
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| A | ||
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