Circuit Description
The diagnostic illuminates the malfunction indicator lamp (MIL) when a non-cylinder specific misfire is present. The powertrain control module (PCM) uses the crankshaft position (CKP) sensor and camshaft position (CMP) sensor to determine engine misfire. The CKP sensor and the CMP sensor monitor their respective components and evaluate changes in the crankshaft rotational speed for each cylinder. Irregular changes in the crankshaft rotational speed indicate a possible misfire. The MIL illuminates when the misfire rate equals or exceeds a pre-determined count. A misfire rate that is high enough can cause the catalytic converter to overheat under certain driving conditions. The MIL will flash ON and OFF when the conditions for catalytic converter overheating are present. Each cylinder is monitored individually for a misfire condition. A DTC P0300 indicates that engine misfire was indicated in more than one cylinder at the same time.
DTC Descriptor
This diagnostic procedure supports the following DTC.
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTC P0107, DTC P0108, DTC P0112, DTC P0113, DTC P0117, DTC P0118, DTC P0122, DTC P0123, DTC P0222, DTC P0223, DTC P0335, DTC P0336, DTC P1128, DTC P1129, DTC P2227, DTC P2228, and DTC P2229 are not set. |
| • | The engine speed is between 500-6,500 RPM. |
| • | The engine coolant temperature (ECT) is more than -10°C (14°F) at start-up. |
| • | The intake air temperature (IAT) sensor 2 is more than -10°C (14°F) at start-up. |
| • | The manifold absolute pressure (MAP) is within a specified range for a calculated engine load. |
| • | DTC P0300 runs continuously once the above conditions are met. |
Condition 1 for Setting the DTC
The PCM detects 30-100 misfires every 200 engine revolutions.
Condition 2 for Setting the DTC
The PCM detects 70 misfires every 1,000 engine revolutions.
Action Taken When the DTC Sets
Condition 1
| • | The PCM flashes the malfunction indicator lamp (MIL) the first time the diagnostic fails indicating that catalytic converter damage can occur. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame data. |
Condition 2
| • | The PCM illuminates the MIL the second time the diagnostic fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | The DTC will clear if there is no misfire detected when the vehicle is operated in the same condition that the misfire was originally set. |
| • | The DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
Check for any of the following conditions:
| • | If any DTCs other than misfire P0301-P0306 are set, diagnose those DTCs first. |
| • | An intermittent ignition system malfunction may cause DTC P0300 to set. Check ignition system performance with an engine oscilloscope. |
| • | Review the misfire counters located in the Engine Data list of the scan tool while the engine is running. If the Misfire Current Cylinder# data parameter is increasing, the misfire condition is present. Misfire activity can be monitored with the scan tool in the Misfire Current Cyl # data list parameter of the appropriate cylinder. Use this information in order to determine if the fault is present or an intermittent malfunction. |
| • | Inspect for good quality recently purchased fuel. Inferior quality fuel or fuel that has aged can cause poor combustion that results in detectable engine misfire. If the fuel is suspect, drain and replace as necessary. |
| • | An intermittent can also be the result of a defective CKP sensor signal rotor. Inspect the CKP signal rotor for nicks, dents, missing teeth, and foreign material. |
| • | Check for engine overheating. Refer to Engine Overheating in Engine Cooling. |
An intermittent malfunction may be caused by a fault in the electrical circuits of the ignition system or fuel system of the misfiring cylinder. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step verifies whether the misfire is present. The scan tool will display increasing counts in one or more of the Misfire Current Cyl. # parameter of the misfiring cylinder when a misfire is occurring.
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If the Misfire Current Counters are incrementing, but the engine is NOT misfiring, this indicates a mechanical condition. For example, an accessory drive belt could cause this condition.
Step | Action | Values | Yes | No | ||||||||||||||||||
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Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views or Splice Pack Connector End Views in Wiring Systems | ||||||||||||||||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||||||||||||
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Important: The engine may only misfire when the engine is under a load. An engine load may be necessary to verify the condition.
Are any of the Misfire Current Counters incrementing? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||||
Is the engine misfiring? | -- | Go to Step 5 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 3.5L (L66) | |||||||||||||||||||
5 | Observe the DTC Info with a scan tool. Is DTC P0201, P0202, P0203, P0204, P0205, P0206, P0335, P0336, P0401, P0403, P0404, P0406, P2647, P2648, or P2649 also set? | -- | Go to Step 6 | |||||||||||||||||||
6 | Is there an engine mechanical noise? | Go to Symptoms - Engine Mechanical in Engine Mechanical - 3.5L (L66) | Go to Step 7 | |||||||||||||||||||
7 | Is there more than one misfire DTC set? | Go to Step 8 | Go to DTC P0301-P0306 | |||||||||||||||||||
8 |
Did you find and correct the condition? | Go to Step 9 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 3.5L (L66) | |||||||||||||||||||
9 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 10 | ||||||||||||||||||
10 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||||
