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 and +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 (CKP) system variation learn 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 CKP system variation learn procedure.
Test Description
The numbers below refer to step numbers on the diagnostic table.
-
Inspect the following components:
-
This step determines if the DTC P0300 is the result of a hard malfunction or an intermittent condition.
-
If the misfire is not present, you may need 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.
-
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.
-
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 are not infinite, this condition will probably not cause a no start but may cause an engine miss during certain conditions.
| • | 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 |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 | Are any other DTCs set? | -- | Go to Step 3 | |||||||||
Did you find and correct any conditions? | -- | Go to Step 27 | Go to Step 4 | |||||||||
Are any Misfire Current counts incrementing? | -- | Go to Step 6 | Go to Step 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 |
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-2.4L. 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 | -- | ||||||||
Important:: Not grounding the IC module assembly may cause erratic spark. Does the spark tester spark on all cylinders? | -- | Go to Step 12 | Go to Step 13 | |||||||||
12 |
Did you find and correct the condition? | -- | Go to Step 27 | Go to Step 9 | ||||||||
13 |
Notice: Refer to Test Lamp to Ignition Control Module Circuit Connector Notice in the Preface section. Did the spark tester spark? | -- | Go to Step 23 | Go to Step 14 | ||||||||
Is the resistance within the specified range? | 4-8K ohms | Go to Step 15 | Go to Step 16 | |||||||||
15 |
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. Does the test lamp blink? | -- | Go to Step 17 | Go to Step 18 | ||||||||
16 |
Is the resistance within the specified range? | 4-8K ohms | Go to Step 20 | Go to Step 21 | ||||||||
17 |
Did you find and correct the condition? | -- | Go to Step 27 | Go to Step 19 | ||||||||
18 |
Did you find and correct the condition? | -- | Go to Step 27 | Go to Step 24 | ||||||||
19 |
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. Does the test lamp illuminate for both circuits? | -- | Go to Step 20 | Go to Step 22 | ||||||||
20 |
Did you find and correct the condition? | -- | Go to Step 27 | Go to Step 21 | ||||||||
21 |
Did you find and correct the condition? | -- | Go to Step 27 | Go to Step 25 | ||||||||
22 |
Did you complete the repair? | -- | Go to Step 27 | -- | ||||||||
23 |
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 replacement? | -- | Go to Step 7 | -- | ||||||||
25 | Replace the affected ignition coil. Refer to Ignition Coil Replacement . Did you complete the replacement? | -- | Go to Step 27 | -- | ||||||||
26 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 27 | -- | ||||||||
27 |
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? | -- | System OK | |||||||||
