Refer to
Ignition System, Knock Sensor
Circuit Description
The PCM has the ability to detect a misfire by monitoring the 3X reference and camshaft position input signals from the Ignition Control Module. The PCM monitors crankshaft speed variations (reference period differences) to determine if a misfire is occurring. If 2% or more of all cylinder firing events are misfires, emission levels may exceed mandated standards. The PCM determines misfire level based on the number of misfire events monitored during a 200 engine revolution test sample. The PCM continuously tracks 16 consecutive 200 revolution test samples. If 11 or more misfires are detected during any 5 of the 16 samples, DTC P0300 will set. If the misfire is large enough to cause possible three-way catalytic converter damage, DTC P0300 may set during the first 200 revolution sample in which the misfire was detected. In the case of a catalyst damaging misfire, the MIL will flash to alert the vehicle operator of the potential of catalyst damage.
Conditions for Setting the DTC
| • | No VSS, TP sensor, MAP sensor, ECT sensor, CKP sensor CMP sensor, or MAF sensor DTCs set. |
| • | Engine speed between 550 and 5900 rpm. |
| • | System voltage between 9 and 16 volts. |
| • | The ECT indicates an engine temperature between -6°C (21.2°F) and 120°C (248°F). |
| • | Throttle angle steady. |
| • | Fuel Cut-Off not active. |
| • | Fuel level greater than 10%. |
| • | Traction control not active. |
| • | The PCM is detecting a crankshaft rpm variation indicating a misfire sufficient to cause Three-Way catalytic converter damage or emissions levels to exceed mandated standard. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. |
| • | The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
The scan tool provides information that can be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as Test 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.
The scan tool displayed misfire counter values (Misfire Hist. #1 through #6) can be useful in determining whether the misfire is isolated to a single cylinder, is isolated to 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, check for the following conditions:
| • | Secondary Ignition Wires: Check wires for affected cylinder pair for disconnected ignition wires or for excessive resistance (the wires should measure under 30,000 ohms (30K ohms). |
| • | Damaged Or Faulty Ignition Coil: Check for cracks, carbon tracking or other damage. Also check coil secondary resistance. Secondary resistance should be between 5000 ohms and 7000 ohms (5K ohms and 7K ohms). |
| • | Substitute a known good coil: Swap ignition coils on the Ignition Control Module and retest. If the misfire follows the coil, replace the ignition coil. Refer to Ignition Coil Replacement . |
If the misfire is random, check for the following conditions:
| • | System Grounds: Ensure all connections are clean and properly tightened. |
| • | MAF: A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the fail records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . |
| • | Air Induction System: Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for disconnected or damaged vacuum hoses, incorrectly installed or faulty PCV valve, or for vacuum leaks at the throttle body, EGR valve, and intake manifold mounting surfaces. Refer to , and Crankcase Ventilation System Description . |
| • | Fuel Pressure: Perform a fuel system pressure test. A faulty fuel pump, plugged filter, or faulty fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test . |
| • | Injector(s): Perform Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) / Fuel Injector Balance Test to locate faulty injector(s) contributing to a lean or flooding condition. In addition to the above test, check the condition of the injector O rings. |
| • | EGR: Check for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow. Refer to Exhaust Gas Recirculation (EGR) System Description . |
| • | Extended Idle: Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures below 80°C (176°F), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 gm/s. |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
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A malfunctioning injector circuit, crankshaft position system variation not learned condition, or incorrect rough road data from the 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.
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The Misfire Current Cyl # display may normally display a small amount of activity (0 - 10 counts) but should not steadily increment during an entire 200 revolution test sample period.
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Depending on the cause of the misfire, the Misfire History Cyl # counter will display a very large number for the misfiring cylinder(s); values for the non-misfiring cylinders will be less than 1/2 as great as the misfiring cylinder(s). When investigating a misfire, always start with items associated with the cylinder(s) that has the largest number of counts stored in the Misfire History Cyl # counter.
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If the misfiring cylinders are companion cylinders, the condition is most likely linked to the ignition system.
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Check for poor terminal connection, grooves, corrosion, pitting, loose fit.
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Check for the following conditions that may contribute to the engine misfire: Engine oil pressure, Damaged accessory drive belt or pulley, Damaged driven accessory (generator, water pump, drive belt tensioner, etc), Loose or broken motor mount(s).
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain on-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
Are any other DTCs set? | -- | Go to applicable DTC | ||||||||||
Is Misfire Current # display incrementing for any cylinder (indicating a misfire currently occurring)? | -- | |||||||||||
View the Misfire History Cyl # display on the scan tool. Does Misfire History Cyl # display a very large value for more than one cylinder? | -- | |||||||||||
Are the misfire values displayed on the Misfire History Cyl # related to companion cylinders (i.e 1/4, 2/5, 3/6)? | -- | |||||||||||
6 |
Was a problem found? | -- | ||||||||||
7 | Check the fuel pressure. Is the fuel pressure within the specified values? | 333-375 kPa (41-47 psi) | Go to the Fuel System Pressure Test | |||||||||
8 |
Was a problem found? | -- | ||||||||||
9 |
Important: : If carbon tracking is apparent at either end of the spark plug wires, replace the affected ignition wire and the associated ignition coil. Was a problem found? | -- | ||||||||||
10 |
Is spark present? | -- | ||||||||||
11 |
Was a problem found? | 600ohms per foot (1 968ohms per meter) | ||||||||||
12 |
Was a problem found? | 5K-8Kohms (5,000-8,000ohms) | ||||||||||
13 |
Was a problem found? | -- | ||||||||||
14 |
Important: : Be sure to reinstall the fuel injector fuse. Does the J 35616-200 test lamp blink? | -- | ||||||||||
15 |
Was a problem found? | -- | Go to Base Engine Misfire Diagnosis | |||||||||
16 |
Was a problem found? | -- | ||||||||||
17 | Reinstall the spark plug. Refer to Spark Plug Replacement .
Was a problem found? | -- | ||||||||||
18 |
Was a problem found? | -- | ||||||||||
19 |
Was a problem found? | -- | Refer to Diagnostic Aids | |||||||||
20 | Replace the ignition coil(s) associated with the misfiring cylinder(s). Refer to Ignition Coil Replacement . Is the action complete? | -- | -- | |||||||||
21 | Replace the ignition control module. Refer to Ignition Control Module Replacement . | -- | -- | |||||||||
22 |
Is Misfire Current Cyl # display incrementing for any cylinder (indicating a misfire currently occurring)? | -- | System OK |
