GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Savana 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 DTC P0300

System Description

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and the camshaft (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring 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 three-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present.

Conditions for Running the DTC

Important: If the start-up ECT is less than 7°C (20°F), misfire detection is delayed until ECT is more than 21°C (70°F). If the start-up ECT is more than 7°C (20°F), misfire detection begins after a 5 second delay.

    • DTCs P0101, P0102, P0103, P0117, P0118, P0128, P0335, P0336, P0341, P0343, P0500, P0502, P0503, P1114, P1115, P1121, P1122, P1220, P1258, P1336, or P1345 are not set.
    • The fuel level is more than 10 percent
    • The engine speed is between 450-5,000 RPM.
    • The system voltage is between 11 and 16 volts.
    • The throttle position (TP) is steady within 2 percent for 100 ms.

Conditions for Setting the DTC

The powertrain control module (PCM) detects a deceleration in the crankshaft speed that is characteristic of either an emission type misfire or of a catalyst-damaging type misfire.

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 misfire index counts the number of misfires. The scan tool can monitor the misfire index. There is a current and a history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring. Use the history misfire counter for misfires that are not currently present.

Many different conditions could cause an intermittent misfire. Check the following conditions:

    • Check the ignition control (IC) circuit for an intermittent short to ground.
    • Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.
    • Ensure that the coil wire is securely attached to the distributor cap and the coil.
    • Check the wire routing to ensure that cross-firing is not occurring.
    • If the misfire occurs when the weather is damp, the problem could be due to worn plug wires.
    • Check the fuel for the following conditions:
       - Condition and quality--Dirty or contaminated fuel could cause a misfire condition.
       - The fuel level--If the fuel level is low, the fuel pump may draw air into the fuel rail, causing a stumble and a possible misfire condition. Check the fuel trim number in the Freeze Frame in order to determine if this has occurred. This condition would be likely if the short term fuel number was more than +20.
       - Restrictions--A restricted fuel filter can also cause a misfire.
    • Check for sticking intake or exhaust valves on engines which misfire when the engine is cold.
    • Check the heated oxygen sensor (HO2S) for abnormal voltage readings.
    • Check for a vacuum leak as a possible cause of the engine misfire.

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If a repair is necessary, refer to Connector Repairs in Wiring Systems.

Test Description

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

  1. The misfire is considered random on all cylinders if the misfire seems to move to different cylinders while you view the misfire fire counters in the misfire data list.

    2.

  2. The misfire is considered consistent if the misfire consistently occurs on the same cylinders.

    3.

  3. The spark should be consistent when you check the spark at the spark plug wires. The presence of few sparks then nothing indicates no spark.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Install the scan tool.

Are any DTCs other than P0135 or P0155 stored?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Start the engine.
  5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
  6. Select the diagnostic trouble code (DTC) option, the Specific DTC option, and then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 5

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Use a spray bottle filled with water in order to wet down the secondary ignition system.
  3. Start the engine.
  4. Monitor the misfire counters in the misfire data list.

Does the scan tool indicate a misfire is present?

--

Go to Electronic Ignition (EI) System Diagnosis

Go to Step 13

5

Is the misfire random on all of the cylinders?

--

Go to Step 10

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Connect the spark tester to the spark plug wire of the cylinders that indicate a misfire.
  3. Start and idle the engine.

Does the tester indicate that the spark is consistent?

--

Go to Step 7

Go to Electronic Ignition (EI) System Diagnosis

7

  1. Remove the spark plugs from the cylinders that indicate a misfire. Refer to Spark Plug Replacement .
  2. Inspect the spark plugs. Refer to Spark Plug Inspection .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 8

8
  1. Install the spark plugs in the cylinders that did not indicate a misfire.
  2. Start the engine.
  3. Monitor the misfire counters in the misfire data list.

Did the misfires change to other cylinders?

--

Go to Step 12

Go to Step 10

9
  1. Perform the Fuel System Diagnostic. Refer to Fuel System Diagnosis .
  2. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

10

Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 .

Did you find a condition?

--

Go to Step 15

Go to Fuel Injector Solenoid Coil Test

11

Replace the spark plugs. Refer to Spark Plug Replacement .

Is the action complete?

--

Go to Step 15

--

12
  1. Check for the following conditions in the following order:
    2. • Contaminated fuel
    • Fouled or damaged spark plugs
    • The ignition coil and connections
    • The distributor cap for damage
    • The exhaust gas recirculation (EGR) valve for leaks
    • The exhaust system for restrictions
    • The PCM grounds
  2. Repair any conditions as necessary.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

13

Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

Is the action complete?

--

Go to Step 14

--

14
  1. Check for engine mechanical problems. Refer to Symptoms - Engine Mechanical in Engine Mechanical - 5.0L and 5.7L.
  2. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 15

Go to Diagnostic Aids

15
  1. Select DTC, then select the Clear DTC Information function on the scan tool.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches the normal operating temperature.
  4. Select DTC, then select the Specific DTC function.
  5. Enter the DTC number which was set.
  6. Operate the vehicle within the Conditions for Setting this DTC until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate that the diagnostic Passed?

--

Go to Step 16

Go to Step 2

16

Does the scan tool display any additional undiagnosed DTCs?

--

Go to Diagnostic Trouble Code (DTC) List

System OK