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 (TCC) disables momentarily in order to determine if the misfire was due to a rough road condition, automatic transmission only.
Conditions for Setting the DTC
| • | The misfire total is greater than 12 counts. |
| • | 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 for a period that is longer than 5 seconds. |
| • | The Throttle Position (TP) has not changed more than 8 percent in 1 second. |
| • | DTC(s) P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0404, P0405, P0503, P0506, P0507, P0601, P0740, P0742, P1133, P1336, P1404 and 1621 are not set. |
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 and a misfire is present. |
| OR |
| The MIL illuminates after two consecutive ignition cycles during in which the diagnostic runs with the fault active |
| OR |
| The MIL illuminates immediately and flashes if a misfire is severe enough to cause any catalyst damage. |
| • | In vehicles with automatic transmission only, the torque converter clutch (TCC) is disablesd when a misfire is present. |
| • | 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 is stored. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed. |
| • | A history DTC clears after 40 consecutive warm up cycles without a fault. |
| • | Clear the MIL/DTCs with a scan tool. |
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 condition of the wheel. Refer to Engine Mechanical section of the service manual.
Verify the electronic Ignition Control Module (ICM) 11 pin harness connector terminal K, ground circuit for less than 0.5 ohms resistance.
Important: A Crankshaft Position System Variation Learning Procedure must be performed at any time that a change is made to the crankshaft sensor to crankshaft relationship. Changing the crank sensor to crankshaft relationship will not allow the PCM to detect a misfire at all speeds and loads accurately, resulting in a possible false misfire DTC being set. Removing a part for inspection and then reinstalling the same part is considered a disturbance. A false DTC P0300 could be set if this procedure is not performed. Refer to Powertrain Control Module (PCM) for the Crankshaft Position System Variation Procedure.
If DTC is intermittent, refer to Symptoms.
Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician 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 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 circuitry.
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A visual/physical inspection should include checking the following components:
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This step determines if the 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 are relatively equal, then the misfire is being caused by something that affects the entire engine. If the accumulators are not equal, this is an indication that the misfire is being caused by something that is specific to two or more cylinders.
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A basic engine problem or fuel injector problem that affects all of the cylinders is possible at this point (e.g. the valve train, the compression, etc.). Refer to the Engine Mechanical portion of the service manual. Also refer to the 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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If a spark plug boot is burned, the other spark plug on that ignition coil may still fire at idle. This step tests the systems 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. Refer to the Engine mechanical portion of the service manual if any plugs are fouled or damaged due to an engine mechanical malfunction.
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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 above 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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If the no spark condition is caused by coil connections, a coil, or a secondary boot assembly, the test light will blink.
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Refer to the Ignition Coils for on vehicle service of the ignition system.
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Refer to the Ignition Coils for on vehicle service of the ignition system.
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Refer to the Ignition Control Module Replacement for on vehicle service of the ignition system.
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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 learning procedure. Refer to the latest Techline procedure for PCM reprogramming and also refer to the Powertrain Control Module (PCM) for the Crankshaft Position System Variation Learning Procedure .
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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 wiring for proper electrical connections, pinches and cuts |
| • | The PCM grounds for being clean and tight |
| • | The vacuum hoses for splits, kinks and proper connections as shown on the Vehicle Emission Information label. Check thoroughly for any type of leak or restriction |
| • | Check the throttle body mounting area and intake manifold sealing surfaces for air leaks. |
| • | 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? | -- | |||
Install a scan tool. Was a DTC P0200 set? | -- | |||
Were any repairs necessary? | -- | |||
Are there any Misfire Current counters incrementing? | -- | |||
Are there any Misfire Current counters incrementing? | -- | |||
Are all the counters equal (within a small percentage of each other)? | -- | |||
7 |
Is the fuel pressure within the specified range? | 211-304kPa (31-44psi) | Go to Fuel System Diagnosis | |
8 | Check the fuel for water, alcohol or other contamination. Is the fuel OK (uncontaminated)? | -- | ||
Is the action complete? | -- | -- | ||
Replace the contaminated fuel. Is the action complete? | -- | -- | ||
Does the spark tester spark on all of the cylinders? | -- | |||
Check for any malfunctioning spark plugs in the cylinders that indicated a misfire. Replace the malfunctioning spark plugs if necessary. Were any spark plugs malfunctioning? | -- | |||
13 |
Notice: Do not leave the jumper wire 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 fused jumper wire from the IC circuit? | -- | ||
Is the resistance between the specified values? | 4-8Kohms | |||
Notice: Do not leave the jumper wire 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 test light blink? | -- | |||
16 |
Is the resistance between the specified values? | 4-8Kohms | ||
17 | Repair the open or short in the ignition coil harness, the poor ignition coil connection or replace the ignition coil, the ignition coil housing or the boot assembly. Is the action complete? | -- | -- | |
18 |
Was a repair necessary? | -- | ||
19 | Visually inspect the ICM 11 pin harness electrical connector in order to see if the connections are clean and tight. Repair the connector as necessary. Were any repairs necessary? | -- | ||
Inspect the following items for corrosion and/or damage for the affected cylinder(s):
Repair the springs, the contacts, and the coil housing as necessary. Is the action complete? | -- | -- | ||
Replace the affected ignition coil. Is the action complete? | -- | -- | ||
Replace the ICM. Is the action complete? | -- | -- | ||
23 | Inspect the PCM electrical connector and connections. Are the connections OK? | -- | ||
Repair the connector or connections. Is the action complete? | -- | -- | ||
Replace the PCM. Is the action complete? | -- | -- | ||
Does the scan tool indicate that these diagnostics have ran and passed? | -- | |||
27 | Check if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK |
