System Description
The powertrain control module (PCM) uses information from the ignition control (IC) module and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring the variations in the crankshaft rotation speed for each cylinder the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the three-way catalytic converter to overheat under certain conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for three-way catalytic converter overheating are present.
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, or P1621 are not set. |
| • | The engine speed is between 469-6,400 RPM. |
| • | The battery voltage is between 9-17 volts. |
| • | The engine coolant temperature (ECT) is between -7 to +123°C (20-254°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 TP has not decreased more than 1.5 percent in 1 second. |
Conditions for Setting the DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed mandated standard.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC 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.
Verify the electronic ignition control module (ICM) 11 pin harness connector terminal K, ground circuit should have less than 0.5 ohms of resistance.
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 Diagnostic System Check-Engine Controls prompts you to complete some of the basic checks and to store the Freeze Frame/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 P0201-P0204 is present, the condition causing the misfire is in the fuel injector circuitry. The DTC P0201-P0204 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 P0301 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, you may need 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 one or more of the following conditions:
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A basic engine problem or a fuel injector problem that affects only one cylinder is possible at this point, such as the valve train, the compression, etc.
If a spark plug is 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 for the following conditions:
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Reprogram the replacement PCM and perform the crankshaft position (CKP) 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 |
| • | A spark plug |
| • | A basic engine problem |
| • | A 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 | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||
Are any injector DTCs set? | -- | 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 counter for the affected cylinder incrementing? | -- | Go to Step 5 | Go to Step 25 | |||||||||
Is the Misfire Current for the affected cylinder counter incrementing? | -- | Go to Step 8 | Go to Step 9 | |||||||||
Did you find and correct the condition? | -- | Go to Step 25 | -- | |||||||||
Did you complete the repair? | -- | Go to Step 25 | -- | |||||||||
Is the resistance between the specified value? | 4-8K ohms | 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? | 4-8K ohms | 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 lead to misdiagnosis. Does the test lamp illuminate for both circuits? | -- | Go to Step 19 | Go to Step 20 | |||||||||
14 |
Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 17 | ||||||||
15 | Check and replace the following items as necessary:
Did you find and correct the condition? | -- | Go to Step 25 | -- | ||||||||
16 | Replace the affected cylinders ignition coil. Refer to the Ignition Coil Replacement . Did you complete the replacement? | -- | 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 timing control 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 |
Did you complete the repair? | -- | Go to Step 25 | -- | ||||||||
21 |
Did you complete the repair? | -- | Go to Step 25 | -- | ||||||||
22 |
Did you complete the replacement? | -- | Go to Step 25 | -- | ||||||||
Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 24 | |||||||||
Replace the PCM. Refer to the Powertrain Control Module Replacement . Did you complete the replacement? | -- | 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? | -- | System OK |
