2001 Chevrolet/Geo Camaro  

DTC P0300

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
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 the mandated standard.

Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
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 Hist #1-#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, perform the CKP System Variation Learn Procedure . The crankshaft position system variation learn procedure should be performed if any of the following conditions are true:

The scan tool displayed misfire counter values (Misfire Hist. #1-#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:

Switch the 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, and 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:

Test Description

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

  1. A malfunctioning injector circuit, a crankshaft position system variation not learned condition, or an 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.

  2. The Misfire Current Cyl # display may normally display a small amount of activity, typically 0-10 counts, but should not steadily increment during an entire 200 revolution test sample period.

  3. 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 values for the misfiring cylinders. When investigating a misfire, always start with conditions associated with the cylinders that have the largest number of counts stored in the Misfire History Cyl # counter.

  4. Steps 5-12 test for conditions that can cause a random cylinder misfire.

  5. Steps 13-23 test for conditions that can cause a non-random or single cylinder misfire.

DTC P0300 - Engine Misfire Detected

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

Are any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

  1. Start and idle the engine.
  2. Review and record the scan tool Freeze Frame data.
  3. Operate the vehicle within the conditions present when the DTC was set.
  4. Monitor the scan tool Misfire Current Cyl # display for each cylinder.

Is Misfire Current # display increments for any cylinder, indicating that a misfire is currently occurring?

--

Go to Step 4

Go to Diagnostic Aids

4

View the Misfire History Cyl # display with a scan tool.

Does Misfire History Cyl # display a very large value for more than 1 cylinder?

--

Go to Step 5

Go to Step 13

5

  1. Inspect the vacuum hoses for splits, for kinks, and for improper connections. Refer to Emission Hose Routing Diagram .
  2. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 6

6

  1. Inspect the crankcase ventilation valve for improper installation and for damaged O-rings.
  2. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 7

7

  1. Inspect the throttle body inlet screen for damage or for the presence of foreign objects that may alter the air flow sample through the MAF sensor.
  2. If a condition is found, repair as necessary. Refer to Throttle Body Air Inlet Screen Replacement .

Did you find and correct the condition?

--

Go to Step  5

Go to Step 8

8

  1. Test the fuel pressure. Refer to Fuel System Diagnosis .
  2. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 9

9

  1. Test the fuel for excessive water, for alcohol, or for other contaminants. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
  2. If a condition was found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 10

10

  1. Inspect the PCM injector grounds, the power grounds, and the sensor grounds to ensure that they are clean, tight, and in their proper locations. Refer to Ground Distribution Schematics in Wiring Systems.
  2. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 11

11

  1. Inspect the following components for vacuum leaks:
    • The intake manifold
    • The EGR adapter
    • The EGR valve
    • The EGR feed pipes
    • The injector O-rings
  2. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 12

12

  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation (EGR) Valve Replacement .
  2. Inspect the valve in order to ensure that the pintle is not sticking partially open.
  3. Inspect the EGR valve pintle and seat for carbon deposits or for burrs that may interfere with the pintle closing completely.
  4. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 13

13

  1. Test for proper fuel injector operation. Refer to Fuel Injector Coil Test .
  2. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 14

14

  1. Inspect the ignition wires associated with the cylinders that were misfiring. Refer to Spark Plug Wire Inspection .
  2. If a condition is found, repair as necessary. Refer to Spark Plug Wire Replacement .

Did you find and correct the condition?

--

Go to Step 25

Go to Step 15

15

  1. Install a J 26792 Spark Tester at the spark plug end of the ignition wire for the cylinder that is indicated by the Misfire Current Cyl # counters or by the Misfire History Cyl # counters as having the most severe misfire, indicated by the largest number of counts.
  2. Jumper the spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil, for example, 1/4; 2/5; 3/6.
  3. Crank the engine while observing the spark tester. A spark should be observed.

Is spark present?

--

Go to Step 20

Go to Step 16

16

Important

If carbon tracking or terminal discoloration is apparent at the ignition coil end of any of the ignition wires, replace the affected ignition wire and the associated ignition coil. Refer to Ignition Coil(s) Replacement .

  1. Remove and inspect the ignition wires associated with the cylinders that were indicated as misfiring. Refer to Spark Plug Wire Inspection . Ensure that the wires and boots are free of carbon tracking, and check the insulation for damage.
  2. If a condition is found, repair as necessary. Refer to Spark Plug Wire Replacement .

Did you find and correct the condition?

--

Go to Step 25

Go to Step 17

17

Measure the resistance of the spark plug wires associated with the cylinders that were indicated as misfiring. Refer to Ignition System Specifications .

Did you find and correct the condition?

--

Go to Step 25

Go to Step 18

18

  1. Remove and inspect the ignition coils associated with the cylinders that were indicated as misfiring. Ensure that the coils and the coil towers are free of cracks and carbon tracking.
  2. If a condition is found, repair as necessary. Refer to Ignition Coil(s) Replacement .

Did you find and correct the condition?

--

Go to Step 25

Go to Step 19

19

  1. Measure the ignition coil secondary resistance.
  2. If resistance is not between the specified values, replace the malfunctioning ignition coils as necessary. Refer to Ignition Coil(s) Replacement .

Did you find and correct the condition?

5 K-8 K ohms

(5000-8000 ohms)

Go to Step 25

Go to Step 24

20

  1. Remove the spark plugs from the cylinders that were indicated as misfiring. Refer to Spark Plug Replacement .
  2. Inspect the spark plug electrodes for excessive fouling. Refer to Spark Plug Inspection .

Did you find and correct the condition?

--

Go to Symptoms - Engine Mechanical in Engine Mechanical

Go to Step 21

21

  1. Inspect the spark plug insulators for cracks, for carbon tracking, or for other damage. Refer to Spark Plug Inspection .
  2. Inspect spark plug electrodes for incorrect gap. Refer to Ignition System Specifications .
  3. If a condition is found, repair as necessary. Refer to Spark Plug Replacement .

Did you find and correct the condition?

--

Go to Step 25

Go to Step 22

22

  1. Inspect for an engine mechanical condition. Refer to Symptoms - Engine Mechanical in Engine Mechanical.
  2. If a condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

23

  1. Inspect for a transaxle torque converter clutch (TCC) condition. Refer to Symptoms - Automatic Transmission in Automatic Transmission-4L60-E.
  2. If a condition is found, repair the transaxle as necessary.

Did you find and correct the condition?

--

Go to Step 25

Go to Diagnostic Aids

24

Replace the ignition control module. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 25

--

25

  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.

Does the DTC run and pass?

--

Go to Step 26

Go to Step 2

26

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

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

--

Go to Diagnostic Trouble Code (DTC) List

System OK