Circuit Description
The crankshaft position (CKP) sensor is mounted through the side of the engine block at the rear of bank 2 above the starter assembly. The CKP sensor works in conjunction with a 24X reluctor wheel on the crankshaft. The reluctor wheel is inside the engine immediately in front of the rear main bearing. The powertrain control module (PCM) provides a 12 volt power supply to the CKP sensor as well as a ground and a signal circuit.
A misfire causes a change in crankshaft speed. The PCM times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in crankshaft speed has occurred. You can expect a certain amount of acceleration or deceleration between each firing stroke, but if the crankshaft speed changes are more than an expected amount, the PCM interprets this as a misfire.
The PCM uses the CKP sensor for misfire detection and to control spark and fueling. As the crankshaft rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 24X signal in combination with the camshaft position (CMP) sensor 1X signal in order to accurately determine crankshaft position. The PCM also calculates a 4X signal from this information. The PCM uses the 4X signal for internal calculations. The 4X signal also provides a tach signal for any device which requires one.
Observe that as long as the PCM receives the CKP sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the CKP sensor 24X signal alone. The CMP sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.
Conditions for Running the DTC
| • | No active mass air flow (MAF) DTCs |
| • | No active engine coolant temperature (ECT) DTCs |
| • | No active throttle position (TP) DTCs |
| • | No active crankshaft position (CKP) sensor DTCs |
| • | No active camshaft position (CMP) sensor DTCs |
| • | No active vehicle speed sensor (VSS) DTCs |
| • | The engine speed is between 375 RPM and 5,001 RPM for automatic transmission. |
| • | The engine speed is between 450 RPM and 5,001 RPM for manual transmission. |
| • | The ignition voltage is between 10 volts and 18 volts. |
| • | The ECT is between -7°C (19°F) and +130°C (+266°F). |
| • | Fuel level more than 10 percent |
| • | The TP sensor angle is steady within 1 percent. |
| • | The antilock brake system (ABS) and traction control systems are not active. |
| • | The transmission is not changing gears. |
| • | The secondary air injection (AIR) diagnostic test is not in progress (RPO NC1 only) |
| • | The A/C clutch is not changing states. |
| • | The PCM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The ABS signal is not exceeding rough road thresholds. |
Conditions for Setting the DTC
| • | The PCM determines that an emission type misfire is present. |
| • | The PCM determines that a catalyst damaging misfire is present. |
Action Taken When the DTC Sets
The PCM illuminates the Malfunction Indicator Lamp (MIL) under the following conditions:
| • | The PCM illuminates the MIL on the second consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions such as load, RPM, temperature, etc. as the previous ignition cycle that the test ran and failed. |
| • | The first time the diagnostic fails, the PCM records the operating conditions in Failure Records. |
| • | The PCM determines the percent of misfire over a 1,000 revolution period is high enough to cause excessive tail pipe emissions. The PCM illuminates the MIL the next consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions such as load, RPM, temperature, etc. as the previous ignition cycle that the test ran and failed. |
| Or |
| • | The PCM flashes the MIL when the diagnostic runs and fails a catalyst damaging misfire. |
Conditions for Clearing the MIL/DTC
Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than the three ignition cycles. Review the Freeze Frame or Failure Records for the last failure conditions.
| • | The PCM turns the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail within the same conditions that the DTC last failed. |
| • | A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | A last test failed clears when the diagnostic runs and does not fail. |
| • | Use a scan tool in order to clear the MIL/DTC. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
| • | Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have fuel level DTCs also set. |
| • | Water contamination in the fuel system can cause a single cylinder to misfire as well as cause a random misfire. If there is a misfire in Cylinder #7 it is possible that water has collected in the fuel rail. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | If there is a misfire detected in Cylinder #4or #6 it is possible that the fuel pressure regulator diaphragm has ruptured, causing fuel to be drawn in through the regulator vacuum line. Remove the vacuum line and inspect for fuel contamination. |
| • | A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis . |
| • | Excessive vibration from sources other than the engine could cause a misfire DTC. The following are possible sources of vibration: |
| - | Variable thickness brake rotor |
| - | Drive shaft not balanced |
| - | Certain rough road conditions |
| • | Observe, if more then one cylinder is misfiring, the scan tool may only display one cylinder misfiring. This will not be apparent until the repair is completed. Also, if an ignition coil ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders misfiring. Inspect the ground circuit for the ignition coil on the cylinder bank of the engine that has more then one cylinder misfiring. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.
If the Misfire Current counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. Perform the diagnostic table for DTC P0335 first if this condition is suspected.
If a misfire is present and you suspect a fuel control problem, force the fuel system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.
A misfire may not be apparent at idle. The misfire may only occur above idle under a load. Road test the vehicle and monitor the misfire current counters.
If more than one cylinder is misfiring, the misfire current counters may only increment for one cylinder. Example: Cylinders 1 and 8 are both misfiring, yet only cylinder 8 increments on the misfire current counter.
If one of the injector fuses is open, only two or three misfire current counters may increment for the corresponding side of the engine.
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The cylinder with the more significant misfire may cause another cylinder counter to increment only by a small amount.
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If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
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An engine mechanical problem can cause a spark plug to gas foul. Inspect for loose rockers, collapsed lifters, or worn camshaft lobes.
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If the customer concern is the MIL flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||||||||||
|
Important:
Are any of the Misfire Current counters incrementing? | -- | |||||||||||||||||||||||||
3 |
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | |||||||||||||||||||||||
Is only one misfire counter incrementing? | -- | |||||||||||||||||||||||||
5 | Visually and physically inspect the following items:
Did any of the above checks isolate a condition requiring a repair? | -- | ||||||||||||||||||||||||
6 |
Important: Before disconnecting the injector harness, refer to Fuel Injection Fuel Rail Assembly Replacement . There is a special procedure for disconnecting the fuel injector harness connectors.
Is the injector test lamp flashing? | -- | ||||||||||||||||||||||||
7 |
Does the spark jump the tester gap and is the spark consistent? | -- | ||||||||||||||||||||||||
8 |
Is the ignition wire resistance less than the specified resistance? | 700 ohms | ||||||||||||||||||||||||
9 | Remove the spark plugs from the cylinder that indicated a misfire. Refer to Spark Plug Replacement in Engine Electrical. Does the spark plug appear to be OK? | -- | ||||||||||||||||||||||||
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Important: If the Injector Coil Test Procedure checks to be OK, refer to Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.
Did the misfire move with the spark plug? | -- | |||||||||||||||||||||||||
11 | Are the spark plugs oil or coolant fouled? | -- | Go to Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L | |||||||||||||||||||||||
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Important: If the fuel system checks to be OK, refer to Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L. Are the spark plugs gas fouled? | -- | Go to Fuel System Diagnosis | ||||||||||||||||||||||||
13 |
Important: If the Injector Coil Test Procedure checks to be OK, refer to Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L. Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | ||||||||||||||||||||||||
14 | Replace or re-gap spark plugs. Refer to Spark Plug Replacement in Engine Electrical. If an improper gap is found, be sure to re-gap spark plugs using a wire type gauge. Is the action complete? | -- | -- | |||||||||||||||||||||||
15 | Replace the faulty spark plugs. Refer to Spark Plug Wire Harness Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||||||||||||||||
16 | Replace the faulty ignition wires. Refer to Spark Plug Wire Harness Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||||||||||||||||
If the customers concern that the MIL was flashing, were any Catalyst DTC's set? | -- | Go to DTC P0420 Catalyst System Low Efficiency Bank 1 or DTC P0430 Catalyst System Low Efficiency Bank 2 | ||||||||||||||||||||||||
18 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||||||||||||||||||||
19 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
