Nissan Sentra B18 (2020-2025) Service Manual: P0171 Fuel Injection System Function

Dtc Description

With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from A/F sensor 1. The ECM calculatesthe necessary compensation to correct the offset between the actual and the theoretical ratios.

In case the amount of the compensation value is extremely large (the actual mixture ratio is too lean), the ECM judges the condition as the fuel injection system malfunction and illuminates the MIL (2 trip detection logic).

DTC DETECTION LOGIC

POSSIBLE CAUSE

• Intake air leakage

• A/F sensor 1

• Fuel injector

• Exhaust gas leakage

• Incorrect fuel pressure

• Lack of fuel

• Mass air flow sensor

• Incorrect PCV hose connection

FAIL-SAFE

Engine Control System

Engine operating condition in fail-safe mode
Fail safe mode		Nissan Sentra Vehicle behavior
Traveling control mode	Accelerator angle variation control	ECM controls the accelerator pedal depression speed to make it slower than actual speed. This causes a drop in accelerating performance and encourages the driver to repair malfunction. Note: ECM does not control the accelerator pedal releasing speed.
Combustion control mode	Stratified charge combustion control at starting	No stratified charge combustion at starting (cold start).
	Idle speed control	Stops feedback control of idle speed and controls with specified speed.
	Recovery speed control at decelerating	Stops recovery speed control by the fuel cut at decelerating and controls with specified speed.
	Idle neutral control	Stops idle neutral control.

Idle Start/Stop System

When a DTC is detected, the start/stop indicator lamp blinks slowly and the idle start/stop system operation is prohibited.

When ECM detects error while operating the idle start/stop system, ECM restarts the engine.

Confirmation Procedure

1. PRECONDITIONING

   If DTC Confirmation Procedure has been previously conducted, always perform the following procedure before conducting the next test.

   >>

   GO TO 2.

2. PERFORM DTC CONFIRMATION PROCEDURE-1

   1. Clear the mixture ratio self-learning value. Refer to DTC Description.

   2. Start engine.

   Is it difficult to start engine?

   YES >>

   GO TO 3.

   NO >>

   GO TO 4.

3. RESTART ENGINE

   If it is difficult to start engine, the fuel injection system has a malfunction, too.

   Crank engine while depressing accelerator pedal.

   Note:

   When depressing accelerator pedal three fourths (3/4) or more, the control system does not start the engine. Do not depress accelerator pedal too much.

   Does engine start?

   YES >>

   Proceed to DTC Diagnosis Procedure.

   NO >>

   Check exhaust and intake air leakage visually.

4. PERFORM DTC CONFIRMATION PROCEDURE-2

   1. Keep engine idle for at least 10 minutes.

   2. Check 1st trip DTC.

   Is 1st trip DTC detected?

   YES >>

   Proceed to DTC Diagnosis Procedure.

   NO >>

   GO TO 5.

5. PERFORM DTC CONFIRMATION PROCEDURE-3

   1. Turn ignition switch OFF and wait at least 10 seconds.

   2. Start engine and Maintain the following conditions for at least 10 consecutive minutes. Hold the accelerator pedal as steady as possible.

      Nissan Sentra Vehicle speed

      50 – 100 km/h (31 – 62 MPH)

      CAUTION:

      Always drive Nissan Sentra vehicle at a safe speed.

   3. Check 1st trip DTC.

   Is 1st trip DTC detected?

   YES >>

   Proceed to DTC Diagnosis Procedure.

   NO-1 >>

   To check malfunction symptom before repair: Refer to Intermittent Incident.

   NO-2 >>

   Confirmation after repair: INSPECTION END

Dtc Diagnosis Procedure

1. CHECK EXHAUST GAS LEAKAGE

   1. Start engine and run it at idle.

   2. Listen for an exhaust gas leakage before three way catalyst (manifold).

      

   Is exhaust gas leakage detected?

   YES >>

   Repair or replace malfunctioning part.

   NO >>

   GO TO 2.

2. CHECK FOR INTAKE AIR LEAKAGE

   1. Listen for an intake air leakage after the mass air flow sensor.

   2. Check PCV hose connection.

   Is intake air leakage detected?

   YES >>

   Repair or replace malfunctioning part.

   NO >>

   GO TO 3.

3. CHECK A/F SENSOR 1 INPUT SIGNAL CIRCUIT

   1. Turn ignition switch OFF.

   2. Disconnect corresponding A/F sensor 1 harness connector.

   3. Disconnect ECM harness connector.

   4. Check the continuity between A/F sensor 1 harness connector and ECM harness connector.

      A/F sensor 1		ECM		Continuity
      Connector	Terminal	Connector	Terminal
      F12	1	F25	86	Existed
      	2		88

   5. Check the continuity between A/F sensor 1 harness connector and ground, or ECM harness connector and ground.

      A/F sensor 1		Ground	Continuity
      Connector	Terminal
      F12	1	Ground	Not existed
      	2

      ECM		—	Continuity
      Connector	Terminal
      F25	86	Ground	Not existed
      	88

   6. Also check harness for short to ground and short to power.

   Is the inspection result normal?

   YES >>

   GO TO 4.

   NO >>

   Repair or replace malfunctioning part.

4. CHECK FUEL PRESSURE

   1. Install all removed parts.

   2. Release fuel pressure to 0. Refer to Work Procedure.

   3. Set a fuel pressure meter and check fuel pressure. Refer to Work Procedure.

      At idle: 3,000 kPa (30.6 kg/cm2, 435 psi)

   Is the inspection result normal?

   YES >>

   GO TO 6.

   NO >>

   GO TO 5.

5. DETECT MALFUNCTIONING PART

   Check fuel hoses and fuel tubes for clogging.

   Is the inspection result normal?

   YES >>

   Replace “fuel filter and fuel pump assembly”. Refer to Removal and Installation.

   NO >>

   Repair or replace malfunctioning part.

6. CHECK MASS AIR FLOW SENSOR

   With CONSULT

   1. Install all removed parts.

   2. Start the engine and warm it up to normal operating temperature.

   3. Check “MASS AIR FLOW SENSOR (Hz)” in “DATA MONITOR” mode of “ENGINE” using CONSULT.

      Monitor item	Condition	Indication
      MASS AIR FLOW SENSOR (Hz)	Ignition switch ON (Engine stopped.)	Approx. 3,700 Hz
      	Idle (Engine is warmed-up to normal operating temperature.)	Approx. 5,500 Hz
      	Idle to about 4,000 rpm	5,500 Hz → 7,000 Hz*

      *: Check for linear frequency rise in response to increase of engine speed.

   Without CONSULT

   1. Install all removed parts.

   2. Start the engine and warm it up to normal operating temperature.

   3. Check the frequency between ECM harness connector terminals under the following conditions.

      ECM			Condition	Frequency
      Connector	+	−
      	Terminal
      F24	26	23	Ignition switch ON (Engine stopped.)	Approx. 3,700 Hz
      			Idle (Engine is warmed-up to normal operating temperature.)	Approx. 5,500 Hz
      			Idle to about 4,000 rpm	5,500 Hz → 7,000 Hz*

      *: Check for linear frequency rise in response to increase of engine speed.

   Is the inspection result normal?

   YES >>

   GO TO 7.

   NO >>

   Check connectors for rusted terminals or loose connections in the mass air flow sensor circuit or grounds. Refer to DTC Diagnosis Procedure.

7. CHECK FUNCTION OF FUEL INJECTOR

   With CONSULT

   1. Start the engine.

   2. Perform “POWER BALANCE” in “ACTIVE TEST” mode of “ENGINE” using CONSULT.

   3. Check that each circuit produces a momentary engine speed drop.

   Without CONSULT

   1. Start the engine and let it idle.

   2. Listen to each fuel injector operating sound.

      Clicking sound should be heard.

      

   Is the inspection result normal?

   YES >>

   INSPECTION END

   NO >>

   Perform trouble diagnosis for fuel injector and circuit, Refer to Diagnosis Procedure.

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