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 MIL. Under light misfire conditions, the PCM may require more than one trip in order 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. For vehicles equipped with an automatic transmission, the torque converter clutch disables momentarily in order to determine if the misfire was due to a rough road condition.
Conditions for Running the DTC
| • | DTCs 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 are not set. |
| • | 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 (20°F) and 123°C (254°F). |
| • | The engine has been running 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 torque converter clutch (TCC) disables when a misfire is present, if the vehicle is equipped with an automatic transmission. |
| • | 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 coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three 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. |
| • | Use a scan tool to clear the DTCs. |
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. Check for porosity and check the condition of the wheel.
Verify that the electronic ignition control module (ICM) 11 pin harness connector terminal K, ground circuit has less than 0.5 ohms of resistance.
If this DTC is intermittent, refer to Symptoms .
When checking the electrical terminal connections with a test lamp or DMM, a malfunctioning electrical terminal connection may be cleaned and not detected as a problem. You may also clean a corroded or dirty electrical terminal connection when disconnecting and reconnecting any electrical connector.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Powertrain OBD System Check prompts the technician to complete some of the basic checks and to store the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data that was captured when the malfunction occurred. The scan tool stores this data for later reference.
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If a DTC P0200 is present, the condition causing the misfire is in the fuel injector circuitry. The DTC P0200 table will diagnose the fuel injectors and the fuel injectors' circuitry.
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A visual and physical inspection should include checking the following components:
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This step determines if DTC P0300 is the result of a hard malfunction or an intermittent condition.
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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.
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If all of the accumulators indicate misfire, then the misfire is being caused by something that affects the entire engine.
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A basic engine problem or a fuel injector problem that affects all of the cylinders is possible at this point. The problem may involve the valve train, the compression, or other parts of the engine. Also refer to DTC P0200 Injector Control Circuit.
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After repairs, verify a no misfire by duplicating the conditions within Freeze Frame Data while watching the misfire counters.
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Important: If the fused jumper wire is not used to ground the ignition control module (ICM) assembly, the system may spark erratically.
If a spark plug boot is burned, the other spark plug on that ignition coil may still fire at idle. This step tests the system's ability to produce at least 25,000 volts at each spark plug.
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Replace any spark plugs that are worn, cracked, or fouled.
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No spark on one coil may be caused by an open secondary circuit. Therefore, the coil's secondary resistance should be checked. 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.
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The test lamp will blink if the no spark condition is caused by the following items:
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Thoroughly check any suspected circuitry for the following conditions:
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Program the replacement PCM and perform the Crankshaft Position System Variation Learn procedure. Refer to the latest Techline™ procedure for PCM reprogramming.
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Conditions for Setting the DTC P0420 need to be performed in order to determine that the catalyst has been damaged from the misfire.
| • | The ignition systems electrical wiring for the following conditions: |
| - | Proper electrical terminal connections |
| - | Pinches in the wires |
| - | Cuts in the wires |
| • | The PCM grounds for being clean and tight |
| • | The vacuum hoses for proper connections as shown on the Vehicle Emission Information label |
| • | The intake manifold sealing surfaces for air leaks |
| • | The ignition coil electrical connections |
| • | The ignition coil |
| • | The secondary boot assembly |
| • | Backed-out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal-to-wire connections |
| • | Physical damage to the wiring harness |
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||||
Are any injector DTCs set? | -- | |||||||||||
Were any repairs necessary? | -- | |||||||||||
Are there any Misfire Current counters incrementing? | -- | |||||||||||
Are there any Misfire Current counters incrementing? | -- | |||||||||||
Was misfire present in all cylinders? | -- | |||||||||||
7 |
Is the fuel pressure within the specified range? | 290-379kPa (42-55psi) | Go to Fuel System Diagnosis | |||||||||
8 |
Is the fuel OK and uncontaminated? | -- | ||||||||||
Check for a basic engine problem. Refer to Base Engine Misfire Diagnosis in Engine Mechanical for the diagnostic procedure. Is the action complete? | -- | -- | ||||||||||
Replace the contaminated fuel. Refer to Fuel System Cleaning . Is the action complete? | -- | -- | ||||||||||
Important: If the fused jumper wire is not used to ground the ICM assembly, the system may spark erratically. Does the spark tester spark on all of the cylinders? | -- | |||||||||||
Were any spark plugs malfunctioning? | -- | |||||||||||
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. Is there a spark present when you remove the test lamp from the IC circuit? | -- | ||||||||||
Is the resistance between the specified values? | 4-8Kohms | |||||||||||
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 other test lamp blink? | -- | |||||||||||
16 |
Is the resistance between the specified values? | 4-8Kohms | ||||||||||
17 |
Was a repair necessary? | -- | ||||||||||
18 |
Was a repair necessary? | -- | ||||||||||
19 |
Important: Carefully handle the ignition coils electrical connectors in order to avoid spark arching from the electrical terminals, causing the IGN fuse to open and to lead to a misdiagnosis. Does the test lamp illuminate for both circuits? | -- | ||||||||||
20 |
Was a repair necessary? | -- | ||||||||||
21 |
Was a repair or replacement necessary? | -- | ||||||||||
22 |
Is the action complete? | -- | -- | |||||||||
23 |
Is the action complete? | -- | -- | |||||||||
24 | Replace the ICM. Refer to Ignition Control Module Replacement . Is the action complete? | -- | -- | |||||||||
25 |
Are the connections OK? | -- | ||||||||||
Repair the electrical connector or the connector terminals. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | ||||||||||
Replace the PCM. Refer to the Powertrain Control Module Replacement . Is the action complete? | -- | -- | ||||||||||
Does the scan tool indicate that these diagnostics ran and passed? | -- | |||||||||||
29 | Check if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
