P0300 code

Good afternoon.

I would check the ignition system first such as plugs, wires and coil. Also, low fuel pressure will cause this code as well.

Roy

CIRCUIT DESCRIPTION
The powertrain control module (PCM) uses information from the ignition control (IC) module and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring the variations in the crankshaft rotation speed for each cylinder the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the three-way catalytic converter to overheat under certain conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for 3-way catalytic converter overheating are present.

CONDITIONS FOR RUNNING THE DTC
DTCs P0101, P0102, P0103, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0336, P0341, P0502, P0503, P1106, P1107, P1114, P1115, P1121, P1122, P1336, or P1374 are not set.
The engine speed is between 550-5850 RPM.
The system voltage is between 9-18 volts.
The engine coolant temperature (ECT) indicates an engine temperature between -6°C (21°F) and 120°C (248°F).
The throttle angle is steady.

CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft RPM variation indicating a misfire sufficient to cause 3-way catalytic converter damage or emissions levels to exceed mandated standard.

ACTION TAKEN WHEN THE DTC SETS
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records.
If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
The scan tool provides information that can be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as DTC status Failed Since Code Clear, the misfire history counters (Misfire #1 through #6) will still contain a value that represents the level of misfire detected on each cylinder.

A misfire DTC may set if components that affect the crankshaft position (CKP) sensor have recently been replaced, and the CKP System Variation Learn Procedure has not been performed. If the diagnostic table does not identify a condition then perform the CKP System Variation Learn Procedure. The Crankshaft Variation Learn Procedure should be performed if any of the following conditions are true:
The PCM has been replaced.
DTC P1336 is set.
The engine has been replaced.
The crankshaft has been replaced.
The crankshaft harmonic balancer has been replaced.
The CKP sensor has been replaced. See: Crankshaft Position Sensor > Procedures

The scan tool displayed misfire counter values (Misfire #1 through #6) can be useful in determining whether the misfire affects a single cylinder, a cylinder pair (cylinders that share an ignition coil (1/4, 2/5, 3/6), or is random. If the largest amount of activity is isolated to a cylinder pair, inspect for the following conditions:
Secondary ignition wires
Check the secondary wires associated with the affected cylinder pair for disconnected ignition wires or for excessive resistance. The wires should measure under 600 ohms per/ft.
Damaged or malfunctioning ignition coil.
Check for cracks, carbon tracking or other damage. Also check coil secondary resistance. Secondary resistance should be between 5000 ohms and 8000 ohms (5K ohms and 8K ohms).

Switch ignition coils and retest. If the misfire follows the coil, replace the ignition coil.

IMPORTANT: If the level of misfire was sufficient to cause possible catalyst damage (if the MIL was flashing), ensure that the DTC P0420 test is completed and passed after verifying the misfire repair.

If the misfire is random, check for the following conditions:
System grounds
Ensure all connections are clean and properly tightened.
Mass air flow sensor
A mass air flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the Failure Records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the Mass Air Flow (MAF) Sensor Replacement.
Damaged accessory drive belt or driven accessory
A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.
Air induction system
Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for disconnected or damaged vacuum hoses, incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, exhaust gas recirculation (EGR) valve, and intake manifold mounting surfaces.
Fuel pressure
Perform a fuel system pressure test. A malfunctioning fuel pump, a plugged filter, or a malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Diagnosis. See: Computers and Control Systems > Component Tests and General Diagnostics
Fuel injectors
Refer to Fuel Injector Coil Test. See: Computers and Control Systems > Component Tests and General Diagnostics
Water contamination in the fuel system can cause a single cylinder to misfire as well as cause a random misfire, refer to Alcohol/Contaminants-In-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool). See: Computers and Control Systems > Component Tests and General Diagnostics See: Computers and Control Systems > Component Tests and General Diagnostics
EGR system
Check for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.
Extended idle
Excessive Open Loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to set, review the Freeze Frame/Failure Records for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures below 80°C (176°F), the condition described above is very likely the cause of the DTC to set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 g/s.

TEST DESCRIPTION

Steps 1-2
image

Steps 3-11
imageZoom/Print

Steps 12-18
imageZoom/Print

Steps 19-26
imageZoom/Print

The numbers below refer to the step numbers on the Diagnostic table.
2. A malfunctioning injector circuit, crankshaft position system variation not learned condition, or incorrect rough road data from the electronic brake control module (EBCM) may cause a misfire DTC to be set. If any of the indicated DTCs are set with DTC P0300, diagnose and repair the other DTC before using the DTC P0300 table.
3. The Misfire Current Cyl # display may normally display a small amount of activity (0-10 counts) but should not steadily increment during an entire 200-revolution test sample period.
4. Depending on the cause of the misfire, the Misfire History Cyl # counter will display a very large number for the misfiring cylinders; values for the non-misfiring cylinders will be less than 1/2 as great as the misfiring cylinders. When investigating a misfire, always start with items associated with the cylinders that have the largest number of counts stored in the Misfire History Cyl # counter.
5. Steps 5-12 test for conditions that can cause a random cylinder misfire.
13. Steps 13-23 test for conditions that can cause a non-random or single cylinder misfire.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator