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 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 disables momentarily in order to determine if the misfire was due to a rough road condition (automatic transmission only).
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 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 two out of eighty ignition cycles when there is a misfire |
| OR |
| The MIL illuminates after two 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 (automatic only) |
| • | The PCM records 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. |
| • | Clear the MIL/DTC(s) with a scan tool. |
Diagnostic Aids
An intermittent can also be the result of a defective reluctor wheel. Remove crankshaft sensor and inspect reluctor wheel through sensor mount hole. Check for porosity and condition of wheel. Refer to DTC P0300 Engine Misfire Detected .
Verify the electronic Ignition Control Module (ICM) 11 pin harness connector terminal K, ground circuit should have less than 0.5 ohms of resistance.
If DTC is intermittent, refer to Symptoms .
When checking the electrical terminal connections with a test lamp or DMM, a malfunctioning electrical terminal connection maybe 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 you 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 captured when the malfunction occurred. The scan tool stores this data on the scan tool 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 circuitry.
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A visual/physical inspection should include checking the following components:
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This step determines if DTC P0303 is the result of a hard malfunction or an intermittent condition.
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If a spark plug boot is burned, the other plug on that ignition coil may still fire at idle. This step tests the systems ability to produce at least 25,000 volts at the spark plug.
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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 a 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, this is an indication that a misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared. The current counter must count a total of at least 195 misfires before writing to the history counter.
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A spark is available at the misfiring cylinder. At this point, the misfire is being caused by the following condition(s):
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A basic engine problem or a fuel injector problem that affects only cylinder #1 is possible at this point, such as a valve train, a compression, etc.
If a spark plug saturated with fuel or the cylinder is full of fuel, this is a good sign that the fuel injector is stuck open.
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Check for a fuel injector or engine mechanical problem that may have caused the spark plug to malfunction.
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No spark on one coil may be caused by an open secondary circuit. Therefore, you will need to check the coils secondary resistance. Resistance readings above 20,000 ohms, but not infinite, will probably not cause a no start but can 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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You can easily check the ignition coil harness by performing the previous step with the ignition coil harness connected to the ICM. Check for a voltage and a ground signal to the ignition coils at the ignition coil electrical connector.
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Thoroughly check any suspected circuitry the following conditions:
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Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming.
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Conditions for setting the DTC P0420 need to be run in order to determine if the catalyst has been damaged from the misfire.
| • | The following in the electrical wiring: |
| - | Proper electrical connections |
| - | Pinches in the wires |
| - | Cuts in the wires |
| • | The PCM grounds for being clean and tight |
| • | Check the following components for air leaks: |
| - | Throttle body mounting |
| - | Intake manifold sealing surfaces |
| • | Spark plug |
| • | Basic engine problem |
| • | Leaky fuel injector |
| • | Ignition coil electrical connections |
| • | Ignition coil harness |
| • | Ignition coil |
| • | Secondary boot assembly |
| • | Backed out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wiring connections |
| • | Physical damage to the wiring harness |
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | ||||||||||
Are any injector DTCs set? | -- | Go to the applicable DTC table | Go to Step 3 | |||||||||
Were any repairs necessary? | -- | Go to Step 25 | Go to Step 4 | |||||||||
Is the Misfire Current #1 counter incrementing? | -- | Go to Step 5 | Go to Step 6 | |||||||||
Does the spark tester spark? | -- | Go to Step 7 | Go to Step 10 | |||||||||
Is the Misfire Current #1 counter incrementing? | -- | Go to Step 5 | Go to Step 25 | |||||||||
Is the Misfire Current #3 counter incrementing? | -- | Go to Step 8 | Go to Step 9 | |||||||||
Is the action complete? | -- | Go to Step 25 | -- | |||||||||
Is the action complete? | -- | Go to Step 25 | -- | |||||||||
Is the resistance between the specified value? | 4-8Kohms | Go to Step 11 | Go to Step 12 | |||||||||
Does the test lamp blink? | -- | Go to Step 13 | Go to Step 14 | |||||||||
12 |
Is the resistance between the specified value? | 4-8Kohms | Go to Step 15 | Go to Step 16 | ||||||||
Important: Carefully handle the ignition coils electrical connectors to avoid spark arching from the electrical terminals and causing the fuse to open which would leading to misdiagnosis. Does the test lamp illuminate for both circuits? | -- | Go to Step 19 | Go to Step 20 | |||||||||
14 |
Were any repairs necessary? | -- | Go to Step 25 | Go to Step 17 | ||||||||
15 | Check and replace the following item(s) as necessary:
Is the action complete? | -- | Go to Step 25 | -- | ||||||||
16 | Replace cylinders #2 and #3 ignition coil. Refer to the Ignition Coil Replacement . Is the action complete? | -- | Go to Step 25 | -- | ||||||||
17 |
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 input circuit? | -- | Go to Step 23 | Go to Step 18 | ||||||||
18 |
Were any repairs necessary? | -- | Go to Step 25 | Go to Step 22 | ||||||||
19 |
Was a repair necessary? | -- | Go to Step 25 | Go to Step 21 | ||||||||
20 |
Is the action complete? | -- | Go to Step 25 | -- | ||||||||
21 |
Is the action complete? | -- | Go to Step 25 | -- | ||||||||
22 |
Is the action complete? | -- | Go to Step 25 | -- | ||||||||
Were any repairs necessary? | -- | Go to Step 25 | Go to Step 24 | |||||||||
Replace the PCM. Refer to the Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 25 | -- | |||||||||
Does the scan tool indicate that these diagnostics have ran and passed? | -- | Go to Step 26 | Go to Step 2 | |||||||||
26 | Check to see 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 |
