Nissan Sentra B18 (2020-2025) Service Manual: P0300 Misfire

Nissan Sentra B18 (2020-2025) Service Manual / Engine / Work Procedure (After Replacing Electric Throttle Control Actuator) / Dtc/circuit Diagnosis / P0300 Misfire

Dtc Description

DTC Description

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the crankshaft position (CKP) sensor signal to vary, ECM can determine that a misfire is occurring.

Sensor	Input signal to ECM	ECM function
Crankshaft position sensor	Engine speed	On board diagnosis of misfire

The misfire detection logic consists of the following two conditions.

One Trip Detection Logic (Three Way Catalyst Damage)

On the 1st trip that a misfire condition occurs that can damage the three way catalyst (TWC) due to overheating, the MIL will blink.

When a misfire condition occurs, the ECM monitors the CKP sensor signal every 200 engine revolutions for a change.

When the misfire condition decreases to a level that will not damage the TWC, the MIL will turn off.

If another misfire condition occurs that can damage the TWC on a second trip, the MIL will blink.

When the misfire condition decreases to a level that will not damage the TWC, the MIL will remain on.If another misfire condition occurs that can damage the TWC, the MIL will begin to blink again.
Two Trip Detection Logic (Exhaust quality deterioration)

For misfire conditions that will not damage the TWC (but will affect Nissan Sentra vehicle emissions), the MIL will only light when the misfire is detected on a second trip. During this condition, the ECM monitors the CKP sensor signal every 1,000 engine revolutions.

DTC DETECTION LOGIC

DTC	CONSULT screen terms (Trouble diagnosis content)	DTC detection condition
P0300	MULTI CYL MISFIRE (Random/Multiple cylinder misfire detected)	Diagnosis condition	—
		Signal (terminal)	—
		Threshold	Multiple cylinders misfire
		Diagnosis delay time	—

POSSIBLE CAUSE

Improper spark plug
Insufficient compression
Incorrect fuel pressure
The fuel injector circuit is open or shorted.
Fuel injector
Intake air leakage
The ignition signal circuit is open or shorted.
Lack of fuel
Signal plate
A/F sensor 1
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

Confirmation Procedure

PRECONDITIONING

If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at least 10 seconds before conducting the next test.

Will CONSULT be used?
YES >>
GO TO 2.
NO >>
GO TO 4.
PERFORM DTC CONFIRMATION PROCEDURE-1

With CONSULT
1. Start the engine and warm it up to normal operating temperature.
2. Turn ignition switch OFF and wait at least 10 seconds.
3. Restart engine and let it idle for about 35 minutes.
4. Check 1st trip DTC.
Is 1st trip DTC detected?
YES >>
Proceed to DTC Diagnosis Procedure.
NO >>
GO TO 3.

PERFORM DTC CONFIRMATION PROCEDURE-2

Turn ignition switch OFF and wait at least 10 seconds.

Start the engine and drive the Nissan Sentra vehicle under similar conditions to (1st trip) Freeze Frame Data for a certain time. Refer to the table below.

Hold the accelerator pedal as steady as possible.

Similar conditions to (1st trip) Freeze Frame Data mean that the following conditions should be satisfied at the same time.

Engine speed	Engine speed in the freeze frame data ± 400 rpm
Nissan Sentra Vehicle speed	Vehicle speed in the freeze frame data ± 10 km/h (6 MPH)
Base fuel schedule	Base fuel schedule in the freeze frame data ± 10%
Engine coolant temperature (T) condition	When the freeze frame data shows lower than 70°C (158°F), T should be lower than 70°C (158°F).
Engine coolant temperature (T) condition	When the freeze frame data shows higher than or equal to 70°C (158°F), T should be higher than or equal to 70°C (158°F).

Driving time varies according to the engine speed in the freeze frame data.

Engine speed	Time
Around 1,000 rpm	Approximately 10 minutes
Around 2,000 rpm	Approximately 5 minutes
More than 3,000 rpm	Approximately 3.5 minutes

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

PERFORM DTC CONFIRMATION PROCEDURE-3

Without CONSULT
1. Start engine and warm it up to normal operating temperature.
2. Turn ignition switch OFF and wait at least 10 seconds.
3. Restart engine and let it idle for about 35 minutes.
4. 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

DTC Diagnosis Procedure

CHECK GROUND CONNECTION

Check the following.
- Connection condition of the ground E9 and E15
- Connection condition of the ground harness between engine assembly and Nissan Sentra vehicle body (If equipped)
Is the inspection result normal?
YES >>
GO TO 2.
NO >>
Repair or replace error-detected parts.
CHECK FOR INTAKE AIR LEAKAGE AND PCV HOSE
1. Start the engine and run it at idle speed.
2. Listen for the sound of the intake air leakage.
3. Check PCV hose connection.
Is intake air leakage detected?
YES >>
Discover air leakage location and repair. Refer to Exploded View.
NO >>
GO TO 3.
CHECK FOR EXHAUST SYSTEM CLOGGING

Stop engine and visually check exhaust tube, three way catalyst and muffler for dents.

Is the inspection result normal?
YES-1 >>
With CONSULT: GO TO 4.
YES-2 >>
Without CONSULT: GO TO 5.
NO >>
Repair or replace malfunctioning part. Refer to Exploded View.
PERFORM POWER BALANCE TEST

With CONSULT
1. Start the engine.
2. Perform “POWER BALANCE”“ACTIVE TEST” mode of “ENGINE” with CONSULT.
3. Check that each circuit produces a momentary engine speed drop.
Is the inspection result normal?
YES >>
GO TO 10.
NO >>
GO TO 5.

CHECK FUNCTION OF FUEL INJECTOR

Without CONSULT

Start engine.

Listen to each fuel injector operation.

Clicking sound should be heard.

Is the inspection result normal?

YES >>

GO TO 6.

NO >>

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

CHECK FUNCTION OF IGNITION COIL-1

CAUTION:

Perform the following procedure in a place with no combustible objects and good ventilation.

Turn ignition switch OFF.
Remove fuel pump fuse in IPDM E/R to release fuel pressure.
Note:
Do not use CONSULT to release fuel pressure, or fuel pressure applies again during the following procedure.
Start engine.
After engine stalls, crank it 2 or 3 times to release all fuel pressure.
Turn ignition switch OFF.
Remove all ignition coil harness connectors to avoid the electrical discharge from the ignition coils.
Remove ignition coil and spark plug of the cylinder to be checked. Refer to Exploded View.
Crank engine for 5 seconds or more to remove combustion gas in the cylinder.
Connect spark plug and harness connector to ignition coil.
Fix ignition coil using a rope etc. with gap of 13 - 17 mm (0.52 - 0.66 in) between the edge of the spark plug and grounded metal portion as shown in the figure.

Crank engine for approximately 3 seconds, and check whether spark is generated between the spark plug and the grounded metal portion.

Spark should be generated.

CAUTION:

Never place the spark plug and the ignition coil within 50 cm (19.7 in) each other. Be careful not to get an electrical shock while checking, because the electrical discharge voltage becomes 20 kV or more.

It might damage the ignition coil if the gap of more than 17 mm (0.66 in) is made.

Note:

When the gap is less than 13 mm (0.52 in), a spark might be generated even if the coil is malfunctioning.

Is the inspection result normal?

YES >>

GO TO 10.

NO >>

GO TO 7.

CHECK FUNCTION OF IGNITION COIL-2

Turn ignition switch OFF.
Disconnect spark plug and connect a non-malfunctioning spark plug.

Crank engine for approximately 3 seconds, and recheck whether spark is generated between the spark plug and the grounded metal portion.

Spark should be generated.

Is the inspection result normal?

YES >>

GO TO 8.

NO >>

Check ignition coil, power transistor and their circuits. Refer to Diagnosis Procedure.

CHECK SPARK PLUG

Check the initial spark plug for fouling, etc.

Is the inspection result normal?
YES >>
Replace spark plug(s) with standard type one(s). Refer to Exploded View.
NO >>
Repair or clean spark plug. Then GO TO 9.

CHECK FUNCTION OF IGNITION COIL-3

Reconnect the initial spark plugs.

Crank engine for approximately 3 seconds, and recheck whether spark is generated between the spark plug and the grounded portion.

Spark should be generated.

Is the inspection result normal?

YES >>

INSPECTION END

NO >>

Replace spark plug(s) with standard type one(s). Refer to Exploded View.

CHECK COMPRESSION PRESSURE

Check compression pressure. Refer to Inspection.

Is the inspection result normal?
YES >>
GO TO 11.
NO >>
Check pistons, piston rings, valves, valve seats and cylinder head gaskets.

CHECK FUEL PRESSURE

Install all removed parts.
Release fuel pressure. Refer to Work Procedure.

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

At idle: Approx. 3,000 kPa (30.0 bar, 30.6 kg/cm², 435 psi)

Is the inspection result normal?

YES >>

GO TO 13.

NO >>

GO TO 12.

DETECT MALFUNCTIONING PART

Check fuel hoses and fuel tubes for clogging.

Is the inspection result normal?
YES >>
Replace “fuel level sensor unit, fuel filter and fuel pump assembly”. Refer to Removal and Installation.
NO >>
Repair or replace malfunctioning part.
CHECK IDLE SPEED AND IGNITION TIMING

Check idle speed and ignition timing.

Idle speed: For procedure, Refer to IDLE SPEED : Periodic Maintenance, for specification, Refer to IDLE SPEED : Periodic Maintenance, for specification, Refer to Service Data.

Ignition timing: For procedure, Refer to IGNITION TIMING : Periodic Maintenance, for specification, Refer to Service Data.

Is the inspection result normal?
YES >>
GO TO 14.
NO >>
Perform basic inspection. Refer to Work Procedure.

CHECK A/F SENSOR 1 INPUT SIGNAL CIRCUIT

Turn ignition switch OFF.
Disconnect corresponding A/F sensor 1 harness connector.
Disconnect ECM harness connector.

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

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

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

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

ECM		—	Continuity
Connector	Terminal	—	Continuity
F25	86	Ground	Not existed
F25	88	Ground	Not existed

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

Is the inspection result normal?

YES >>

GO TO 15.

NO >>

Repair or replace malfunctioning part.

CHECK A/F SENSOR 1 HEATER

Refer to Component Inspection.

Is the inspection result normal?
YES >>
GO TO 16.
NO >>
Replace malfunctioning A/F sensor 1. Refer to Exploded View.

CHECK MASS AIR FLOW SENSOR OUTPUT VOLTAGE

With CONSULT

Install all removed parts.
Start engine and warm it up to normal operating temperature.

Select “MASS AIR FLOW SENSOR (Hz)” in “DATA MONITOR” mode using CONSULT and check the indication under the following condition.

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

Install all removed parts.
Start engine and warm it up to normal operating temperature.

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

ECM			Condition	Frequency
Connector	+	−
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 17.

NO >>

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

CHECK SYMPTOM MATRIX CHART

Check items on the rough idle symptom in Symptom Table.

Is the inspection result normal?
YES >>
GO TO 18.
NO >>
Repair or replace malfunctioning part.
ERASE THE 1ST TRIP DTC

Some tests may cause a 1st trip DTC to be set.

Erase the 1st trip DTC from the ECM memory after performing the tests. Refer to Diagnosis Description.

>>
INSPECTION END

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