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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2007 🢒 Vibe - FWD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0300

Circuit Description

The DTC P0300 Engine Misfire Detected diagnostic illuminates the malfunction indicator lamp (MIL) when a not cylinder specific misfire is present. The powertrain control module (PCM) uses the crankshaft position (CKP) sensor and camshaft position (CMP) sensor to determine engine misfire. The CKP sensor and the CMP sensor monitor their respective components and evaluate changes in the crankshaft rotational speed for each cylinder. Irregular changes in the crankshaft rotational speed indicate a possible misfire. The MIL illuminates when the misfire rate equals or exceeds a pre-determined count. A misfire rate that is high enough can cause the catalytic converter to overheat under certain driving conditions. The MIL will flash ON and OFF when the conditions for catalytic converter overheating are present. Each cylinder is monitored individually for a misfire condition. A DTC P0300 indicates that engine misfire was indicated in more than one cylinder at the same time.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0300 Engine Misfire Detected

Conditions for Running the DTC
    • DTCs P0100, P0101, P0102, P0103, P0110, P0112, P0113, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0325, P0327, P0328, P0335, P0340, P0341, P0385, P0500, P0850 are not set.
    • The engine speed is between 450-6,700 RPM.
    • The battery voltage is between at least 8 volts.
    • The intake air temperature (IAT) is at least -10°C (+14°F).
    • The engine coolant temperature (ECT) is at least -10°C (+14°F).
    • The mass air flow (MAF) sensor indicates there is at least 0.12 gram of air per engine revolution.
    • Throttle position is changing less than 0.5 degrees per every 8 milliseconds.
    • DTC P0300 runs continuously once the above condition is met.

Conditions for Setting the DTC
    • The rough road counter in the PCM indicates that there are normal road conditions.
    • The engine misfire is random or indicated in more than one cylinder simultaneously.

Action Taken When the DTC Sets
    • The PCM flashes the MIL the first time catalytic converter damage can occur.
    • The PCM illuminates the MIL the second time the diagnostic fails.
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. The PCM also freezes the engine speed at Misfire and the Load at Misfire scan tool data parameters at the time the MIL illuminates.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL after 3 consecutive trips without a fault.
    • The PCM clears a History DTC after 40 consecutive warm-up cycles without a fault.
    • You use the scan tool Clear DTC Information function.

Diagnostic Aids
    • Check for the following conditions:
       - If any DTCs other than misfire (P0300 to P0304) are present, diagnose those DTCs first.
       - If DTCs P0301, P0302, P0303, or P0304 are also present with DTC P0300, diagnose those DTCs first.
       - An intermittent ignition system malfunction may cause DTC P0300 to set. Check the ignition system performance with an engine oscilloscope.
       - The scan tool data parameters Engine Speed at Misfire and Load at Misfire are populated and frozen at the time the MIL illuminates. These scan tool displays can be used like additional lines of Freeze Frame data. Review the information located in the Engine Speed at Misfire and the Load at Misfire scan tool parameters. The information can help determine engine operation when the misfire occurred.
       - Review the misfire counters located in the Misfire Data list of the scan tool while the engine is running. If any of the Misfire Current Cylinder data parameters is increasing, the misfire condition is present. Misfire activity can be monitored with the scan tool in the Misfire Current Cyl # data list parameter of the appropriate cylinder. Use this information in order to determine if the fault is present or an intermittent malfunction.
       - An intermittent can also be the result of a defective CKP sensor signal rotor. Remove the CKP sensor and inspect the signal rotor through the sensor hole. Check the condition of the signal rotor for nicks, dents, missing teeth, and foreign material.
       - A MAF sensor output that is incorrect may cause the PCM to command the fuel system to go lean. Check the performance of the MAF sensor. If the heated oxygen sensor (HO2S) voltage is fixed low, while the fuel trim is constantly high, check the MAF sensor signal circuit for resistance. High circuit resistance can cause the sensor to read a lower volume of air than actual, resulting in a lean fueling condition that can cause engine misfire.
       - Check for engine overheating.
       - Check for a positive crankcase ventilation (PCV) system malfunction. Perform a functional check of the PCV valve.
    • An intermittent malfunction may be caused by a fault in the ignition system or fuel system electrical circuits. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
    • Repair any electrical circuit faults that were found. Refer to Wiring Repairs .
    • The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

Test Description

The numbers below refer to the step numbers in the diagnostic table.

  1. The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool, if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step verifies whether the misfire is present. The scan tool will display increasing counts in the Total Misfire Current Count parameter if a misfire is occurring.

    3.

  3. This step checks whether the DTC P0300 is the result of a hard failure or an intermittent condition. Operating the vehicle in Check mode enhances the diagnostic capabilities of the PCM. For additional information on Check mode operation, refer to the Powertrain Control Module Diagnosis. The scan tool will display increasing counts in the Total Misfire Current Count parameter if a misfire is occurring.

    4.

  4. This step tests for adequate secondary ignition voltage. The fuel injectors are disabled in order to prevent unburned fuel from accumulating in the cylinders.

    5.

  5. This step inspects for a condition that can reduce the secondary ignition voltage to the spark plug. Step 6 verified that the ignition coil output is satisfactory. This step will qualify the remaining secondary ignition system components.

    6.

  6. Contaminants in the fuel, such as alcohol or water, can create a misfire condition.

    7.

  7. A vacuum leak can cause a lean misfire condition.

    8.

  8. Operating the vehicle in Check Mode enhances the diagnostic capabilities of the PCM. The catalytic converter diagnostic can be monitored on the scan tool under the I/M System Information selection. When the Catalyst test displays a YES status, indicating that the catalytic converter system diagnostic is completed, check for DTC P0420 in the Last Test Failed screen of the scan tool. If there is no DTC P0420 displayed, the catalytic converter diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Is DTC P0301, P0302, P0303, or P0304 also set?

--

Go to DTC P0301-P0304

Go to Step 3

3

  1. Install a scan tool.
  2. Start the engine.
  3. Monitor the Total Misfire Current Count parameter on the scan tool.

Did the scan tool indicate any misfire counts?

--

Go to Step 5

Go to Step 4

4

  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check mode, using the scan tool.
  3. Operate the vehicle within the Freeze Frame conditions as specified.
  4. Monitor the Total Misfire Current Count parameter on the scan tool.

Did DTC P0300 set or did the scan tool indicate any misfire counts?

--

Go to Step 5

Go to Diagnostic Aids

5

  1. Disconnect all the fuel injector electrical connectors.
  2. Remove the ignition coil 1 . Refer to Ignition Coil Replacement .
  3. Connect the ignition coil electrical connector.
  4. Connect a J 26792 Spark Tester or an equivalent to the ignition coil 1 boot.
  5. Crank the engine and observe the spark tester.
  6. A crisp, blue spark should be observed.
  7. Install the ignition coil.
  8. Repeat steps 2-5 for each of remaining the ignition coils.

Was a crisp blue spark present every engine revolution for each ignition coil?

--

Go to Step 7

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Exchange the ignition coils. Replace the suspected faulty ignition coil with a coil that produced good spark.
  3. Connect a J 26792 or an equivalent to the ignition coil boot.
  4. Crank the engine while observing the spark tester.

Was a crisp, blue spark present every engine revolution?

--

Go to Step 14

Go to Electronic Ignition (EI) System Diagnosis

7

  1. Perform a visual and physical inspection of the ignition coil boots and spark plugs for the following conditions:
    2. • Water intrusion
    • Corroded or poor connections to the spark plugs
    • Carbon tracking
  2. Repair the condition or replace the faulty component as necessary. Refer to Ignition Coil Replacement or Spark Plug Replacement .

Was a repair necessary?

--

Go to Step 16

Go to Step 8

8
  1. Remove the spark plugs. Refer to Spark Plug Replacement .
  2. Visually and physically inspect the spark plugs for the correct operation and good performance. Refer to Spark Plug Inspection .
  3. Clean or replace the spark plug as necessary. Refer to Spark Plug Replacement .

Was a faulty spark plug condition found and repaired?

--

Go to Step 16

Go to Step 9

9
  1. Turn OFF the ignition.
  2. Disconnect all 4 fuel injector electrical connectors.
  3. Install a J 34730-2B Fuel Injector Test Lamp, or equivalent, into each fuel injector harness connector.
  4. Observe the injector test lamp for each fuel injector while cranking the engine.

Does the fuel injector test lamp flash for each injector while cranking the engine?

--

Go to Step 10

Go to Fuel Injector Circuit Diagnosis

10

Perform the Fuel Injector Coil Test and the Fuel Injector Balance Test procedures. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test with Special Tool .

Did any fuel injectors require replacement?

--

Go to Step 16

Go to Step 11

11
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  4. Install a scan tool.
  5. Turn ON the ignition, with the engine OFF.
  6. Select Fuel Pump in the Engine Output Controls menu of the scan tool.
  7. Turn ON the fuel pump, using the scan tool.
  8. Observe the fuel pressure indicated by the fuel pressure gage with the fuel pump running.

Is the fuel pressure within the specified range?

301-347 kPa (44-50 psi)

Go to Step 12

Go to Fuel System Diagnosis

12

  1. Check a fuel sample for the following concerns:
    2. • Any alcohol or other contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • The fuel type and quality
  2. Replace the fuel as necessary.

Was a repair necessary?

--

Go to Step 16

Go to Step 13

13

  1. Visually and physically inspect the following for vacuum leaks:
    2. • The positive crankcase ventilation (PCV) valve
    • The intake manifold gasket
    • The vacuum lines, the vacuum hoses, and the fittings
    • Inspect for incorrect vacuum hose routing.
  2. Repair as necessary.

Did you find and correct a condition?

--

Go to Step 16

Go to Step 15

14

Replace the faulty ignition coil. Refer to Ignition Coil Replacement .

Is the action complete?

--

Go to Step 16

--

15
  1. Check for any of the following engine mechanical concerns:
    2. • Worn or faulty camshaft
    • Leaky or sticky valves
    • Excessive valve deposits
    • Weak valve springs
    • Incorrect valve timing
    • Intake manifold runner leaks or obstructions
    • Broken or worn piston rings
    • Leaking head gasket
  2. Repair as necessary. Refer to Diagnostic Starting Point - Engine Mechanical .

Was a basic engine mechanical concern found and repaired?

--

Go to Step 16

Go to Diagnostic Aids

16

  1. In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, place the vehicle in Check Mode. Refer to Service Bay Test .
  2. While in Check Mode, operate the vehicle within the conditions for running and setting DTC P0420 and verify that DTC P0420 runs and passes. Refer to DTC P0420 .

Does DTC P0420 run and pass?

--

Go to Step 17

Go to DTC P0420

17
  1. Perform the scan tool Clear DTC Information function.
  2. Operate the vehicle within the Freeze Frame conditions that set the DTC.
  3. Monitor the Total Misfire Current Count parameter on the scan tool.

Did a DTC set or did the scan tool indicate any misfire counts?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK