GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Alero Export 🢒 DTC 🢒 DTC P0300

System 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 three-way catalytic converter overheating are present.

Conditions for Running the DTC
    • DTCs P0105, P0107, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0336, P0340, P0341, P0342, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, or P1621 are not set.
    • The engine speed is between 469-6,400 RPM.
    • The battery voltage is between 9-17 volts.
    • The engine coolant temperature (ECT) is between -7 to +123°C (20-254°F).
    • The engine has been running for more than 5 seconds.
    • The throttle position (TP) has not increased more than 8 percent in 1 second.
    • The TP has not decreased more than 1.5 percent in 1 second.

Conditions for Setting the DTC

The misfire total is more than 8 counts.

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

An intermittent can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the sensor mount hole. Inspect for porosity and the general condition of the wheel.

Verify that the ignition control (IC) module ground circuit has less than 0.5 ohms resistance.

Important: The crankshaft position system variation learning procedure must be performed any time a change is made to the crankshaft sensor to crankshaft relationship. Changing the crank sensor to crankshaft relationship will not allow the PCM to detect a misfire at all speeds and loads accurately, resulting in a possible false misfire DTC being set. Removing a part for inspection and then reinstalling the same part is considered a disturbance. A false DTC P0300 could be set by not performing the Crankshaft Position System Variation Learning procedure.

Test Description

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

  1. The visual/physical inspection should also include the following components:

    2. • The ignition system electrical wiring for the following conditions:
       - The correct electrical terminal connections
       - Any pinches or cuts in the wires
    • Clean and tight PCM grounds
    • The proper connections of the vacuum hoses, as shown on the Vehicle Emission Information label
    • Any air leaks at the intake manifold sealing surfaces

  2. This step determines if the DTC P0300 is the result of a hard malfunction or an intermittent condition.

    3.

  3. If the misfire is not present, it may be necessary to duplicate the conditions in the Freeze Frame data in order to detect the misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. If the misfire accumulators start to increment, then this indicates that the misfire is present. A sudden change in the throttle, a rough road, or other crankshaft rotation disturbances may cause the counter to increment a few counts and then stop. This can be considered normal and should not be diagnosed as a misfire. The history counter begins counting after the DTC is set and will indicate only true misfires. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared.

    4.

  4. If a spark plug boot is burned, the other spark plug on that ignition coil may still fire at idle. This step tests the systems ability to produce at least 25,000 volts at each spark plug.

    5.

  5. No spark on one coil may be caused by an open secondary circuit. Therefore, the coils secondary resistance should be tested. If the resistance readings are MORE THAN 20,000 ohms, but not infinite, this will probably not cause a no start but may cause an engine miss under certain conditions.

    6.

  6. The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.

DTC P0300-Engine Misfire Detected

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Are any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List/Type

Step 3

3

  1. Turn OFF the ignition.
  2. Perform a visual and physical inspection. Refer to Symptoms - Engine Controls .
  3. If a problem is found, repair as necessary.

Did you find and correct any conditions?

--

Go to Step 27

Go to Step 4

4

  1. Start the engine and idle the engine.
  2. Use the scan tool in order to observe the Misfire Current Counts.

Are any Misfire Current counts incrementing?

--

Go to Step 6

Go to Step 5

5

Operate the vehicle within the Freeze Frame data and the Conditions for Running the DTC as specified in the supporting text.

Are any Misfire Current counts incrementing?

--

Go to Step 6

Go to Diagnostic Aids

6

Is misfire present in all cylinders?

--

Go to Step 7

Go to Step 11

7

Perform the Fuel System Diagnosis .

Did you find and correct the condition?

--

Go to Step 27

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Perform the Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find contaminated fuel?

--

Go to Step 10

Go to Step 9

9

Inspect for basic engine problems. Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Did you find and correct any conditions?

--

Go to Step 27

--

10

Perform the Fuel System Cleaning .

Did you complete the repair?

--

Go to Step 27

--

11

  1. Turn OFF the ignition.
  2. Remove the fuel pump relay.
  3. Remove the IC assembly keeping the IC assembly connected to the harness connector. Refer to Ignition Control Module Replacement .

    4. Important:: Not grounding the IC module assembly may cause erratic spark.

  4. Connect a fused jumper from the IC module assembly to ground.
  5. Install the J 36012-A Spark Plug Jumper Wire Kit.
  6. Install a J 26792 Spark Tester on the #1 spark plug jumper wire.
  7. Ground the #4 spark plug jumper wire. The #4 wire is the companion to #1.
  8. Crank the engine with the remaining spark plug wires connected.
  9. Repeat the above steps by installing the spark tester on #4 and grounding #1. Do the same for the #2 and the #3 spark plugs. Make sure the companion wire is grounded.

Does the spark tester spark on all cylinders?

--

Go to Step 12

Go to Step 13

12
  1. Turn OFF the ignition.
  2. Inspect for malfunctioning spark plugs in the cylinders that indicated a misfire. Refer to Spark Plug Inspection in Engine Electrical.
  3. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 9

13
  1. Disconnect the PCM connector.
  2. Reconnect the J 26792 on the spark plug jumper wire that did not spark.
  3. Ground the companion spark plug jumper wire.
  4. Turn ON the ignition, with the engine off.
  5. Connect a test lamp to B+.

    6. Notice: Refer to Test Lamp to Ignition Control Module Circuit Connector Notice in the Preface section.

  6. Momentarily touch the affected IC timing control circuit at the PCM connector. A spark should be present when the test lamp is removed from the circuit.

Did the spark tester spark?

--

Go to Step 23

Go to Step 14

14

  1. Turn OFF the ignition.
  2. Remove the spark plug jumper wires from the affected cylinder and the companion at the coil housing.
  3. Connect a DMM between the secondary ignition coil terminals.

Is the resistance within the specified range?

4-8K ohms

Go to Step 15

Go to Step 16

15
  1. Remove the ignition coil housing from the cover.
  2. Disconnect the ignition coil harness connector at the IC module.
  3. Connect two test lamps to B+.
  4. Probe the affected ignition coil control terminal at the IC module with one of the test lamps.
  5. Turn ON the ignition, with the engine OFF.

    6. Notice: Do not leave the test lamp connected to the PCM IC circuit connector for longer than 5 seconds at a time. Failure to do so may damage the ignition coil and/or the Ignition Control Module.

  6. Momentarily touch the affected IC timing control circuit at the PCM connector with one test lamp while monitoring the other test lamp.

Does the test lamp blink?

--

Go to Step 17

Go to Step 18

16
  1. Remove the ignition coil housing.
  2. Disconnect the ignition coil connector from the IC module.
  3. Remove the affected ignition coil from the housing.
  4. Retest the resistance between the secondary terminals of the coil.

Is the resistance within the specified range?

4-8K ohms

Go to Step 20

Go to Step 21

17
  1. Turn OFF the ignition.
  2. Test the coil control circuit between the IC module and the affected ignition coil for the following conditions:
    3. • An open
    • A short to ground
    • A short to voltage
    • A poor connection at the ignition coil or at the IC module
  3. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 19

18
  1. Turn OFF the ignition.
  2. Disconnect the IC module 11 pin connector.
  3. Test the affected IC timing control input circuit between the IC module and the PCM for the following conditions:
    4. • An open
    • A short to ground
    • A short to voltage
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 24

19
  1. Disconnect the ignition coil connector from the affected ignition coil.
  2. Reconnect the ignition coil connector to the IC module.
  3. Connect a test lamp to ground.

    4. Important:: Carefully handle the ignition coil connectors to avoid spark arching from the terminals and causing the fuse to open which would lead to a misdiagnosis.

  4. Turn ON the ignition, with the engine OFF.
  5. Probe the ignition feed circuit at the coil connectors one at a time with the test lamp.

Does the test lamp illuminate for both circuits?

--

Go to Step 20

Go to Step 22

20
  1. Inspect the affected cylinder and the companion for corrosion or damage to the following components:
    2. • The spark plug boot
    • The ignition coil springs
    • The ignition coil housing
  2. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 21

21
  1. Inspect the ignition coil and the PCM terminals of the affected coil for poor connections
  2. If a problem is found, repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 25

22
  1. Turn OFF the ignition.
  2. Repair the open in the ignition 1 circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

23
  1. Turn OFF the ignition.
  2. Inspect the PCM connector and terminals for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 26

24

Replace the IC. Refer to Ignition Control Module Replacement .

Did you complete the repair?

--

Go to Step 27

--

25

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

Did you complete the repair?

--

Go to Step 27

--

26

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the repair?

--

Go to Step 27

--

27
  1. Use a scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 28

Go to Step 2

28

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK