Refer to
Power, Ground, KS,CMP,CKP,Coils, and ICM
.
System Description
The Powertrain Control Module (PCM) monitors both the crankshaft and the camshaft position in order to detect an engine misfire. A rapid decrease in the crankshaft speed indicates misfire. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and before illuminating the malfunction indicator lamp (MIL). Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under a severe misfire, the PCM flashes the MIL. A flashing MIL indicates that there is a misfire that is capable of damaging the catalytic converter. The torque converter clutch (TCC) disables momentarily in order to determine if the misfire was due to a rough road condition (automatic transmission only).
Conditions for Running the DTC
| • | The following DTCs are not set: P0105, P0107, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, and P1621. |
| • | The engine speed is between 469 RPM and 6400 RPM |
| • | The battery voltage is between 9 volts and 17 volts. |
| • | The engine coolant temperature (ECT) is between -7°C and +123°C (20°F- 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 throttle position (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 malfunction indicator lamp (MIL) illuminates if the fault is active within the same conditions for 2 out of 80 ignition cycles when there is a misfire. |
| OR |
| • | The MIL illuminates after 2 consecutive ignition cycles in which the diagnostic runs with the fault being active, |
| OR: |
| • | The MIL illuminates immediately and flashes if a misfire is severe enough to cause any catalyst damage. |
| • | The TCC disables when a misfire is present (automatic only). |
| • | The PCM records the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The engine cooling fan turns on. |
Conditions for Clearing the DTC
| • | The MIL turns off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed. |
| • | A history DTC clears after 40 consecutive warm up cycles without a fault. |
| • | Clear 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. Refer to Crankshaft Balancer Cleaning and Inspection in Engine Mechanical.
Verify that the ignition control module (ICM) 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. Refer to Crankshaft Position System Variation Learn .
If the DTC is intermittent, refer to Cuts Out, Misses .
Test Description
The numbers below refer to step numbers on the diagnostic table.
-
The visual/physical inspection should also include 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, 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.
-
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 not infinite, this will probably not cause a no start but may cause an engine miss under certain conditions.
-
The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.
| • | 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 | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | 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 Base Engine Misfire Diagnosis 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 | -- | ||||||||
Important:: Not grounding the ICM 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: 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. Did the spark tester spark? | -- | Go to Step 23 | Go to Step 14 | ||||||||
Is the resistance wiithin 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 IGN 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 ICM. 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 | -- | ||||||||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the repair? | -- | Go to Step 27 | -- | |||||||||
27 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
