GSIC - Global Service Information Center

### 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)

## for Preparation Click here

## 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 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 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

When air-fuel ratio feedback is stable after warming up engine, fuel trim is considered to be in error on LEAN side
(2 trip detection logic)

1. Air induction system
2. Injector blockage
3. Mass air flow meter
4. Engine coolant temperature sensor
5. Fuel pressure
6. Gas leakage in exhaust system
7. Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
8. A/F sensor (bank 1, 2 sensor 1)
9. A/F sensor heater (bank 1, 2 sensor 1)
10. A/F relay
11. PCV piping
12. ECM

P0172
P0175

When air-fuel ratio feedback is stable after warming up the engine, fuel trim is considered to be in error on RICH side
(2 trip detection logic)

1. Injector leak or blockage
2. Mass air flow meter
3. Engine coolant temperature sensor
4. Ignition system
5. Fuel pressure
6. Gas leakage in exhaust system
7. Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
8. A/F sensor (bank 1, 2 sensor 1)
9. A/F sensor heater (bank 1, 2 sensor 1)
10. A/F relay
11. ECM

HINT:

1. 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.
2. If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 may be recorded. The MIL then illuminates.
3. If the total of the short-term fuel trim value and long-term fuel trim value is within +-35% (engine coolant temperature is more than 75°C (167°F)), the system is functioning normally.

## MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the ECM's estimated fuel injection volumes also affects the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air-fuel ratio). If the average fuel trim learning value exceeds the malfunction threshold, the ECM interprets this 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.

## WIRING DIAGRAM

Refer to DTC P2195 (Click here).

## INSPECTION PROCEDURE

HINT:

  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 A/F sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.

  The following instructions describe how to conduct the A/F control operation using the intelligent tester.

1. (a) Connect the intelligent tester to the DLC3.
2. (b) Start the engine and turn the tester ON.
3. (c) Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
4. (d) On the tester, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
5. (e) 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).
6. (f) Monitor the voltage outputs of the A/F and heated oxygen sensors (AFS B1S1 (AFS B2S1) and O2S B1S2 (O2S B2S2)) displayed on the tester.

HINT:

1. The A/F control operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
2. Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Standard:

  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 (heated oxygen sensor) | +25% | Rich | More than 0.55
  O2S B1S2 or O2S B2S2 (heated oxygen) | -12.5% | Lean | Less than 0.4

NOTICE:

  The Air-fuel Ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

Case | A/F Sensor (Sensor 1) Output Voltage | Heated Oxygen 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 |  | Output voltage More than 0.55 V Less than 0.4 V |

2

Injection volume
+25%
-12.5%

Injection volume
+25%
-12.5%

1. A/F sensor
2. A/F sensor heater
3. A/F sensor circuit

Output voltage Almost no reaction |  | Output voltage More than 0.55 V Less than 0.4 V |

3

Injection Volume
+25%
-12.5%

Injection volume
+25%
-12.5%

1. Heated oxygen sensor
2. Heated oxygen sensor heater
3. Heated oxygen sensor circuit

Output voltage More than 3.35 V Less than 3.0 V |  | Output voltage Almost no reaction |

4

Injection volume
+25%
-12.5%

Injection volume
+25%
-12.5%

1. Injector
2. Fuel pressure
3. Gas leakage from exhaust system
   (air-fuel ratio is extremely lean or rich)

Output voltage Almost no reaction |  | Output voltage Almost no reaction |

HINT:

1. Read freeze frame data using the intelligent tester. 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.
2. 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.
3. 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.

1.CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)

1. Connect the intelligent tester to the DLC3.

1. Turn the ignition switch ON and turn the tester ON.

1. Enter the following menus: Powertrain / Engine and ECT / DTC.

1. Read the 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.

| B |

GO TO RELEVANT DTC CHART

A |

2.CHECK CONNECTION OF PCV HOSE

OK:
  PCV hose is connected correctly and is not damaged.

| NG |

REPAIR OR REPLACE PCV HOSE

OK |

3.CHECK AIR INDUCTION SYSTEM

1. Check the air induction system for vacuum leaks.

| NG |

REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK |

4.PERFORM ACTIVE TEST (A/F CONTROL)

1. Connect the intelligent tester to the DLC3.

1. Start the engine and turn the tester ON.

1. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.

1. On the tester, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

1. 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).

1. Monitor the voltage outputs of A/F and heated oxygen sensors (AFS B1S1 (AFS B2S1) and O2S B1S2 (O2S B2S2)) displayed on the tester.

HINT:

1. The A/F control operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
2. Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Standard:

  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 (heated oxygen sensor) | +25% | Rich | More than 0.55
  O2S B1S2 or O2S B2S2 (heated oxygen sensor) | -12.5% | Lean | Less than 0.4

Result:

  Status AFS B1S1 (AFS B2S1) | Status O2S B1S2 (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

  1. PCV valve and hose
  2. PCV hose connection
  3. Injector blockage
  4. Gas leakage from exhaust system
  5. Air induction system
  6. Fuel pressure
  7. Mass Air Flow (MAF) meter
  8. Engine Coolant Temperature (ECT) sensor

  A

  Rich

  Rich

  Actual air-fuel ratio rich

  -

  1. Injector leakage or blockage
  2. Gas leakage from exhaust system
  3. Ignition system
  4. Fuel pressure
  5. MAF meter
  6. ECT sensor

  A

  Lean

  Lean / Rich

  A/F sensor malfunction

  -

  1. A/F sensor

  B

  Rich

  Lean / Rich

  A/F sensor malfunction

  -

  1. A/F sensor

  B

HINT:

  Lean: During A/F control, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the heated oxygen 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.

| B |

Go to step 11

| C |

Go to step 15

A |

5.READ DATA LIST (ENGINE COOLANT TEMPERATURE)

1. Connect the intelligent tester to the DLC3.

1. Turn the ignition switch ON and turn the tester ON.

1. Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp.

1. Read the Coolant Temp value twice, when the engine is cold and also when warmed up.

   Standard:
     With cold engine: Same as ambient temperature
     With warm engine: Between 75°C and 95°C (167°F and 203°F)

| NG |

REPLACE ENGINE COOLANT TEMPERATURE SENSOR

OK |

6.READ DATA LIST (MASS AIR FLOW METER)

1. Connect the intelligent tester to the DLC3.

1. Turn the ignition switch ON and turn the tester ON.

1. Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp and MAF.

1. Allow the engine to idle until the coolant temp value reaches 75°C (167°F) or more.

1. 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 1.4 and 2.3 gm/s (shift position: N; A/C: OFF).
     MAF at engine speed of 2,500 rpm: Between 5.4 and 7.9 gm/s (shift position: N; A/C: OFF).

| NG |

REPLACE MASS AIR FLOW METER

OK |

7.CHECK FUEL PRESSURE

1. Check the fuel pressure (high or low pressure).

| NG |

REPAIR OR REPLACE FUEL SYSTEM

OK |

8.CHECK FOR EXHAUST GAS LEAKAGE

1. Check for exhaust gas leakage from the exhaust manifold and pipe.

   OK:
     No exhaust gas leakage.

| NG |

REPAIR OR REPLACE EXHAUST SYSTEM

OK |

9.CHECK FOR SPARK AND IGNITION

HINT:

  If the spark plugs or ignition system malfunction, engine misfires may occur. The misfire counter can be read with the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 (to #6) Misfire Rate.

| NG |

REPAIR OR REPLACE IGNITION SYSTEM

OK |

10.INSPECT FUEL INJECTOR

HINT:

  If the injectors malfunction, engine misfires may occur. The misfire counter can be read with the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List.

| NG |

REPLACE FUEL INJECTOR ASSEMBLY

OK |

11.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

1. Disconnect the A/F sensor connector.

1. Measure the resistance of the A/F sensor.

   Standard resistance:

     Tester Connection | Specified Condition
     1 (HT) - 2 (+B) | 1.8 to 3.4 Ω at 20°C (68°F)
     1 (HT) - 4 (AF-) | 10 kΩ or higher

| NG |

REPLACE AIR FUEL RATIO SENSOR

OK |

12.INSPECT RELAY (Marking: A/F)

1. Remove the A/F heater relay from the engine room relay block.

1. Measure the resistance of the relay.

   Standard resistance:

     Terminal No. | Specified Condition
     3 - 5 | 10 kΩ or higher
     3 - 5 | Below 1 Ω (when battery voltage is applied to terminals 1 and 2)

| NG |

REPLACE RELAY

OK |

13.CHECK WIRE HARNESS (A/F SENSOR - ECM)

1. Disconnect the A18 or A25 A/F sensor connector.

1. Disconnect the E6 ECM connector.

1. Measure the resistance of the wire harness side connectors.

   Standard resistance:

     Terminal Connection | Specified Condition
     A18-1 (HT) - E16-2 (HA1A) | Below 1 Ω
     A18-3 (AF+) - E16-22 (A1A+) | Below 1 Ω
     A18-4 (AF-) - E16-30 (A1A-) | Below 1 Ω
     A25-1 (HT) - E16-1 (HA2A) | Below 1 Ω
     A25-3 (AF+) - E16-23 (A2A+) | Below 1 Ω
     A25-4 (AF-) - E16-31 (A2A-) | Below 1 Ω
     A18-1 (HT) or E16-2 (HA1A) - Body ground | 10 kΩ or higher
     A18-3 (AF+) or E16-22 (A1A+) - Body ground | 10 kΩ or higher
     A18-4 (AF-) or E16-30 (A1A-) - Body ground | 10 kΩ or higher
     A25-1 (HT) or E16-1 (HA2A) - Body ground | 10 kΩ or higher
     A25-3 (AF+) or E16-23 (A2A+) - Body ground | 10 kΩ or higher
     A25-4 (AF-) or E16-31 (A2A-) - Body ground | 10 kΩ or higher

| NG |

REPAIR OR REPLACE HARNESS AND CONNECTOR

OK |

14.REPLACE HEATED OXYGEN SENSOR

NEXT |

15.PERFORM CONFIRMATION DRIVING PATTERN

NEXT |

16.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)

1. Connect the intelligent tester to the DLC3.

1. Turn the ignition switch ON and turn the tester ON.

1. Enter the following menus: Powertrain / Engine and ECT / DTC.

1. Read the DTC.

   Result:

     Display (DTC output) | Proceed to
     P0171, P0172, P0174 or P0175 are not output again | A
     P0171, P0172, P0174 or P0175 are output again | B

| B |

Go to step 5

A |

END