SFI SYSTEM (w/ Secondary Air Injection System), Diagnostic DTC:P0300, P0301, P0302, P0303, P0304

DTC Code	DTC Name
P0300	Random / Multiple Cylinder Misfire Detected
P0301	Cylinder 1 Misfire Detected
P0302	Cylinder 2 Misfire Detected
P0303	Cylinder 3 Misfire Detected
P0304	Cylinder 4 Misfire Detected

DESCRIPTION

When the engine misfires, high concentrations of hydrocarbons (HC) enter the exhaust gas. Extremely high HC concentration levels can cause an increase in exhaust emission levels. High concentrations of HC can also cause increases in the Three-Way Catalytic Converter (TWC) temperature, which may cause damage to the TWC. To prevent this increase in emissions and to limit the possibility of thermal damage, the ECM monitors the misfire rate. When the temperature of the TWC reaches the point of thermal degradation, the ECM blinks the MIL. To monitor misfires, the ECM uses both the Camshaft Position (CMP) sensor and the Crankshaft Position (CKP) sensor. The CMP sensor is used to identify any misfiring cylinders and the CKP sensor is used to measure variations in the crankshaft rotation speed. Misfires are counted when the crankshaft rotation speed variations exceed predetermined thresholds.

If the misfire exceeds the threshold levels, and could cause emission deterioration, the ECM illuminates the MIL and sets a DTC.

DTC No.	DTC Detection Conditions	Trouble Areas
P0300	Simultaneous misfiring of several cylinders detected (2 trip detection logic)	Open or short in engine wire harness Connector connection Vacuum hose connections Ignition system Fuel injector Fuel pressure Mass Air Flow (MAF) meter Air induction system Engine Coolant Temperature (ECT) sensor Compression pressure Valve clearance Valve timing PCV valve and hose PCV hose connections ECM
P0301 P0302 P0303 P0304	Misfiring of specific cylinder detected (2 trip detection logic)	Open or short in engine wire harness Connector connection Vacuum hose connections Ignition system Fuel injector Fuel pressure Air induction system Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor Compression pressure Valve clearance Valve timing PCV valve and hose PCV hose connections ECM

DTC No.

DTC Detection Conditions

Trouble Areas

P0300

Simultaneous misfiring of several cylinders detected

(2 trip detection logic)

Open or short in engine wire harness
Connector connection
Vacuum hose connections
Ignition system
Fuel injector
Fuel pressure
Mass Air Flow (MAF) meter
Air induction system
Engine Coolant Temperature (ECT) sensor
Compression pressure
Valve clearance
Valve timing
PCV valve and hose
PCV hose connections
ECM

P0301

P0302

P0303

P0304

Misfiring of specific cylinder detected

(2 trip detection logic)

Open or short in engine wire harness
Connector connection
Vacuum hose connections
Ignition system
Fuel injector
Fuel pressure
Air induction system
Mass Air Flow (MAF) meter
Engine Coolant Temperature (ECT) sensor
Compression pressure
Valve clearance
Valve timing
PCV valve and hose
PCV hose connections
ECM

Tech Tips

When DTCs for misfiring cylinders are randomly set, but DTC P0300 is not set, misfires have been detected in different cylinders at different times. DTC P0300 is only set when several misfiring cylinders are detected at the same time.

Reference: Inspection using an oscilloscope

With the engine idling, check the waveform between terminals #1 to #4 and E01 of the ECM connectors.

Item	Contents
Terminals	#1 to #4 - E01
Equipment Settings	20 V/Division, 100 or 1 ms/Division
Conditions	Idling

Tech Tips

The correct waveform is as shown below.

MONITOR DESCRIPTION

The ECM illuminates the MIL and sets a DTC when either one of the following conditions, which could cause emission deterioration, is detected (2 trip detection logic).

Within the first 4,000 crankshaft revolutions of the engine starting, an excessive misfiring rate (approximately 20 to 50 misfires per 4,000 crankshaft revolutions) occurs once.
After the first 4,000 crankshaft revolutions, an excessive misfiring rate (approximately 20 to 60 misfires per 4,000 crankshaft revolutions) occurs 4 times in sequential crankshaft revolutions.

The ECM flashes the MIL and sets a DTC when either one of the following conditions, which could cause the Three-Way Catalytic Converter (TWC) damage, is detected (2 trip detection logic).

In every 200 crankshaft revolutions at a high engine rpm, the threshold misfiring percentage is recorded once.
In every 200 crankshaft revolutions at a normal engine rpm, the threshold misfiring percentage is recorded 3 times.

WIRING DIAGRAM

Refer to DTC P0351 Click here for the wiring diagram of the ignition system.

CONFIRMATION DRIVING PATTERN

Connect an intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Record the DTC(s) and freeze frame data.
Using the tester, switch the ECM from normal mode to check mode Click here.
Read the misfire counts of each cylinder (Cyl #1 to #4) with the engine in an idling condition. If any misfire count is displayed, skip the following confirmation driving pattern.

Drive the vehicle several times with the conditions, such as engine rpm and engine load, shown in Misfire RPM and Misfire Load in the Data List.

Tech Tips

In order to store misfire DTCs, it is necessary to drive the vehicle for the period of time shown in the table below, with the Misfire RPM and Misfire Load in the Data List.

Engine RPM	Duration
Idling	8 minutes or more
1,000	4.5 minutes or more
2,000	2.5 minutes or more
3,000	1.5 minutes or more

Check whether misfires have occurred by checking DTCs and freeze frame data.

Tech Tips

Do not turn the ignition switch to OFF until the stored DTC(s) and freeze frame data have been recorded.

When the ECM returns to normal mode (default), the stored DTC(s), freeze frame data and other data will be erased.
Record the DTC(s), freeze frame data and misfire counts.
Turn the ignition switch to OFF and wait for at least 5 seconds.

INSPECTION PROCEDURE

Tech Tips

If any DTCs other than the misfire DTCs are output, troubleshoot those DTCs first.
Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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.
If the misfire does not recur when the vehicle is brought to the workshop, reproduce the conditions stored in the freeze frame data.
The misfire still cannot be reproduced even though the conditions stored in the freeze frame data have been duplicated, one of the following factors is considered to be a possible cause of the problem:

The fuel tank is low full.
Improper fuel is used.
The spark plugs have been contaminated.
The problem is complex.

After finishing repairs, check the misfire counts of the cylinders (Cyl #1, #2, #3, and #4).
Be sure to confirm that no misfiring cylinder DTCs are set again by conducting the confirmation driving pattern, after repairs.
For 6 and 8 cylinder engines, the ECM intentionally does not set the specific misfiring cylinder DTCs at high engine RPM. If misfires occur only in high engine RPM areas, only DTC P0300 is set.

In the event of DTC P0300 being present, perform the following operations:

Clear the DTC Click here.
Start the engine and conduct the confirmation driving pattern.
Read the misfiring rates of each cylinder or DTC(s) using the tester or scan tool.
Repair the cylinder(s) that has a high misfiring rate or is indicated by the DTC.
After finishing repairs, conduct the confirmation driving pattern again, in order to verify that DTC P0300 is not set.

When one of Short FT #1 or Long FT #1 in the freeze frame data is outside the range of +-20%, the air-fuel ratio may be rich (-20% or less) or lean (+20% or more).
When the Coolant Temp in the freeze frame data is less than 75°C (167°F), the misfires have occurred only while warming up the engine.
An extremely imbalanced drive wheel which causes body vibration may cause misfire DTCs to be detected.

PROCEDURE

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO MISFIRE DTCS)

Connect an intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / DTC.

Read DTCs.

Result

Display (DTC Output)	Proceed To
P0300, P0301, P0302, P0303, and/or P0304	A
P0300, P0301, P0302, P0303, and/or P0304 and other DTCs	B

Tech Tips

If any DTCs other than P0300, P0301, P0302, P0303 and P0304 are output, troubleshoot those DTCs first.

GO TO DTC CHART

READ VALUE USING INTELLIGENT TESTER (MISFIRE RPM AND MISFIRE LOAD)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch to ON and turn the tester on.
3. Enter the following menus: Powertrain / Engine and ECT / Data List / Misfire RPM and Misfire Load.
4. Read and note the Misfire RPM and Misfire Load (engine load) values.
  
  Tech Tips
  
  The Misfire RPM and Misfire Load indicate the vehicle conditions under which the misfire occurred.
NEXT
CHECK PCV HOSE
1. Check the PCV hose connections.
  
  OK
  
  PCV hose is connected correctly and is not damaged.
NG
REPAIR OR REPLACE PCV HOSE

OK

OK
PCV hose is connected correctly and is not damaged.

CHECK MISFIRE COUNT (CYL #1, #2, #3 AND #4)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Clear DTCs Click here.
Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (Cyl #1, #2, #3 and #4).
Allow the engine to idle.
Read each value of Cyl #1 to #4 displayed on the tester. If no misfire counts occur in any cylinders, perform the following operations:
1. Shift the gear selector lever to the D position.
2. Repeat steps (e) to (g) above.
3. Check the Cyl #1 to #4.
4. If misfire counts are still not displayed, perform steps (h) and (i) and then check the misfire counts again.
Drive the vehicle with the Misfire RPM and Misfire Load noted in step 2.

Read the Cyl #1 to #4 or DTCs displayed on the tester.

Result

Misfire Count	Proceed To
One or two cylinders have misfire counts	A
Three cylinders or more have misfire counts	B

CHECK AIR INDUCTION SYSTEM Click here

CHECK SPARK PLUG
1. Check the spark plug of the misfiring cylinder Click here.
NG
REPLACE SPARK PLUG

OK
CHECK SPARK AND IGNITION
1. Disconnect the fuel injector connectors in order to prevent the engine from starting.
2. Install the spark plug to the ignition coil.
3. Attach the spark plug assembly to the cylinder head cover.
4. Crank the engine for less than 2 seconds and check the spark.
  
  OK
  
  Sparks jump across electrode gap
5. Reconnect the fuel injector connectors.
NG
CHANGE TO NORMAL SPARK PLUG AND CHECK SPARK Click here

OK
CHECK CYLINDER COMPRESSION PRESSURE
1. Measure the cylinder compression pressure of the misfiring cylinder.
OK
INSPECT ECM TERMINAL OF MISFIRING CYLINDER (#1, #2, #3 AND/OR #4 VOLTAGE) Click here

NG

CHECK ENGINE TO DETERMINE CAUSE OF LOW COMPRESSION
CHANGE TO NORMAL SPARK PLUG AND CHECK SPARK
1. Change the installed spark plug to a spark plug that functions normally.
2. Perform a spark test.
  
  CAUTION:
  
  Always disconnect each fuel injector connector.
  
  Note
  
  Do not crank the engine for more than 2 seconds.
  1. Install the spark plug to the ignition coil and connect the ignition coil connector.
  2. Disconnect the fuel injector connector.
  3. Ground the spark plug.
  4. Check if sparks occur while the engine is being cranked.
    
    OK
    
    Sparks jump across electrode gap.
NG
REPLACE IGNITION COIL ASSEMBLY

OK

REPLACE SPARK PLUG

OK
Sparks jump across electrode gap

OK
Sparks jump across electrode gap.

INSPECT ECM TERMINAL OF MISFIRING CYLINDER (#1, #2, #3 AND/OR #4 VOLTAGE)

Text in Illustration

*a
Component with wire harness connected

(ECM)

Turn the ignition switch to ON.

Text in Illustration
*a	Component with wire harness connected (ECM)

Measure the voltage between the terminals of the ECM connector.

Voltage

Tester Connection	Specified Condition
D3-6 (#1) - D1-7 (E01)	11 to 14 V
D3-5 (#2) - D1-7 (E01)	11 to 14 V
D3-2 (#3) - D1-7 (E01)	11 to 14 V
D3-1 (#4) - D1-7 (E01)	11 to 14 V

CHECK FUEL INJECTOR ASSEMBLY Click here

CHECK HARNESS AND CONNECTOR (FUEL INJECTOR - ECM)

Text in Illustration
*a	Front view of wire harness connector (to Fuel Injector)
*b	Rear view of wire harness connector (to ECM)

Disconnect the fuel injector connector (of the misfiring cylinder).

Disconnect the ECM connectors.
Turn the ignition switch to ON.

Measure the resistance and voltage according to the value(s) in the table below.

Standard (Cylinder No.1)

Tester Connection	Specified Condition
D24-1 - Ground	11 to 14 V
D24-2 - Ground	10 kΩ or higher
D24-2 - D3-6 (#1)	Below 1 Ω

Standard (Cylinder No.2)

Tester Connection	Specified Condition
D25-1 - Ground	11 to 14 V
D25-2 - Ground	10 kΩ or higher
D25-2 - D3-5 (#2)	Below 1 Ω

Standard (Cylinder No.3)

Tester Connection	Specified Condition
D26-1 - Ground	11 to 14 V
D26-2 - Ground	10 kΩ or higher
D26-2 - D3-2 (#3)	Below 1 Ω

Standard (Cylinder No.4)

Tester Connection	Specified Condition
D27-1 - Ground	11 to 14 V
D27-2 - Ground	10 kΩ or higher
D27-2 - D3-1 (#4)	Below 1 Ω

Reconnect the fuel injector connector.
Reconnect the ECM connector.

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK FUEL INJECTOR ASSEMBLY
1. Check the fuel injector injection (whether fuel volume is high or low, and whether injection pattern is poor).
NG
REPLACE FUEL INJECTOR ASSEMBLY

OK
CHECK VALVE CLEARANCE
1. Check the valve clearance.
NG
ADJUST VALVE CLEARANCE

OK
CHECK AIR INDUCTION SYSTEM
1. Check the air induction system for vacuum leakage.
  
  OK
  
  No leakage from air induction system.
NG
REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK
CHECK VALVE TIMING
1. Check the valve timing Click here.
NG
ADJUST VALVE TIMING

OK
CHECK FUEL PRESSURE
1. Check the fuel pressure.
NG
CHECK AND REPLACE FUEL PUMP, PRESSURE REGULATOR, FUEL PIPE LINE AND FILTER

OK

OK
No leakage from air induction system.

READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / 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°C and 95°C (167°F and 203°F).

REPLACE ENGINE COOLANT TEMPERATURE SENSOR

READ VALUE USING INTELLIGENT TESTER (MAF)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / 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 2.0 gm/s and 4.5 gm/s (shift position: N, A/C: OFF).
MAF at engine speed of 2,500 rpm
Between 8.0 gm/s and 14.7 gm/s (shift position: N, A/C: OFF).

REPLACE INTAKE AIR FLOW METER SUB-ASSEMBLY

CHECK FOR INTERMITTENT PROBLEMS