P0300

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

CIRCUIT DESCRIPTION
The Crankshaft Position (CKP) sensors send pulses to the PCM as the slots in the reluctor rotate past each sensor. From a correlation of the CKP pulses, the PCM calculates a reference pulse. The PCM uses the reference pulse to detect an engine misfire. The PCM calculates the time period between each pulse, and monitors the time to detect a change in the speed of the crankshaft. The PCM allows for a certain amount of crankshaft speed variation. However, when the change is more than an expected amount, the PCM will interpret the change as a misfire. If 2 percent or more of all cylinder firing events are misfires, emission levels may exceed the mandated standards. The PCM monitors misfire in blocks of data. Each block consists of 200 engine revolutions. The PCM counts the number of misfires occurring in each block. If the number of misfires exceeds the calibrated amount in a specific number of blocks, DTC P0300 will set

CONDITIONS FOR RUNNING THE DTC
^ No VSS, TP, MAP, ECT, CKP, CMP, MAF sensor, IC, or Transmission DTCs set
^ Engine speed is between 500-5850 RPM.
^ System voltage is between 9-18 volts.
^ The ECT indicates an engine temperature between -7°C (19°F) and 120°C (248°F).
If start-up ECT is below -7°C (19°F), then the test is delayed until ECT is more than 21°C (70°F).
^ Throttle angle steady.
^ A/C compressor clutch steady.
^ EGR flow test is inactive.
^ Fuel Level is above 10 percent
^ DFCO and Torque Management not active.

CONDITIONS FOR SETTING THE DTC
5 out of 16 consecutive 200 revolution blocks containing 22 or more misfires is considered non- catalyst damaging misfire.
OR
Any 200 revolution block containing an excessive amount of misfires (above a predetermined threshold) is considered catalyst damaging misfire.

ACTION TAKEN WHEN THE DTC SETS
^ If the misfire level is non-catalyst damaging, the PCM will illuminate the MIL during the second key cycle in which the DTC sets.
^ If the misfire is severe enough to cause possible catalyst damage, the PCM will immediately flash the MIL while the misfire remains at catalyst damaging levels.
^ The PCM will disable TCC operation.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
Any data previously stored in Freeze Frame will be overwritten when this DTC sets. The only exception to this is if a fuel trim DTC was already recorded in Freeze Frame. In this case, the fuel trim data stays in Freeze Frame and the Misfire Data will be stored in Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL off after three consecutive trips that the diagnostic has been run and passed.
Note that if the last failure was during a non-typical driving condition, the MIL may remain on longer than three drive trips. Review Freeze Frame for the last failure conditions.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS
Check for the following conditions:
^ Incorrect CKP System Variation data stored in the PCM. Run the CKP System variation Learn Procedure using the scan tool.
^ System Grounds - Ensure all connections are clean and properly tightened.
^ 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.
^ Fuel Pressure - Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test Fuel System Pressure Test
^ Fuel injectors - Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F). Component Tests and General Diagnostics Component Tests and General Diagnostics
^ Contaminated Fuel - Refer to Alcohol/Contaminants-in-Fuel Diagnosis. Component Tests and General Diagnostics
^ 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 be set, review the freeze frame and failure records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 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 P0300 being 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.
^ Running the vehicle low on fuel - This DTC may set if the vehicle misfires while running out of fuel. If no misfire is currently present, but the History Counters indicate random misfire was once present, ask if the vehicle has been run out of fuel. If this is the case, no further repair may be necessary.

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 condition is intermittent, refer to Intermittent Conditions in Symptoms. Intermittent Conditions

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Engine misfire can change engine load characteristics which may affect the TP sensor performance diagnostic. Correct any misfire before diagnosing DTC P0121. A malfunctioning injector circuit, crankshaft position system variation not learned, an intermittent CKP sensor problem, incorrect rough road data from the EBCM, etc. may cause a misfire DTC to be set. If any other DTCs are set with DTC P0300 (except P0121), diagnose and repair the other DTC before using the DTC P0300 table.
3. The Misfire Bar Graph (or 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.
5. Certain mechanical conditions may cause the PCM to detect a misfire, but you will not be able feel or hear the engine misfiring.
10. Certain conditions will cause more than one cylinder to misfire.
19. If the customer's concern is the MIL is flashing, this indicates that a catalyst damaging misfire occurred. Operate the engine within the conditions to run DTC P0420.