Circuit Description
The Crankshaft Position sensor is mounted through the side of the engine block at the rear of Bank 2 behind the starter assembly. The Crankshaft Position 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 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/deceleration between each firing stroke, but if the crankshaft speed changes are greater than an expected amount, the PCM interprets this as a misfire.
The PCM uses the Crankshaft Position sensor for both 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 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 Crankshaft Position sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position 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
| • | DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, P1120, P1220, P1221, P1258 did not set. |
| • | The engine speed is between 425 RPM and 3000 RPM. |
| • | The ignition voltage is between 10 volts and 18 volts. |
| • | The engine coolant temperature is between -7°C (19°F) and 130°C (266°F). |
| • | The fuel level is greater than 10 percent. |
| • | The throttle angle is steady within 1 percent. |
| • | The ABS and the traction control are not active. |
| • | The transmission is not changing gears. |
| • | The AIR diagnostic test is not in progress. |
| • | The A/C clutch is in a steady state. |
| • | The engine is not in fuel shut-off or decel fuel cut-off. |
| • | The ABS signals are 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 will illuminate the Malfunction Indicator Lamp (MIL) under the following conditions:
| • | The PCM illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails, if the diagnostic fails under the same conditions (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 second consecutive drive trip that this diagnostic fails [under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed], the PCM stores this information in Freeze Frame. The PCM copies any data previously stored in Freeze Frame and copies the data into the Failure Records. The PCM then overwrites the Freeze Frame. The only exception to this is if a Misfire DTC was already recorded in Freeze Frame. In this case, the Misfire data stays in Freeze Frame and the PCM updates the Fuel Trim data in the Failure Records. |
| • | The PCM determines the percent of misfire over a 1000 revolution period is high enough to cause excessive tail pipe emissions. The PCM illuminates the Malfunction Indicator lamp the next consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed. |
| • | The PCM determines the percent of misfire is high enough to cause Catalytic Converter damage. The PCM flashes the Malfunction Indicator lamp when the diagnostic runs and fails. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed. |
| 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/Failure Records for the last failure conditions. |
| • | 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 (Current DTC) 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\TAC module connector surfaces before
servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets
when diagnosing/replacing the modules. Ensure that the gaskets are
installed correctly. The gaskets prevent contaminate intrusion into
the PCM\TAC modules. • For any test that requires probing the PCM or a component
harness connector, use the Connector Test Adapter Kit J 35616
. Using this kit prevents damage
to the harness/component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
| • | Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have DTCs P0461/P1431 also set. |
| • | A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis . |
| • | A misfire that only occurs during certain conditions may be difficult to locate. Observe freeze frame and/or failure records to determine when the DTC set. |
| • | Excessive vibration from sources other than the engine could cause a misfire DTC. The following are possible sources of vibration: |
| - | Variable thickness brake rotor |
| - | Propeller shaft not balanced |
| - | Certain rough road conditions |
| • | Observe, if more than one cylinder is mis-firing, the scan tool may only display one cylinder mis-firing. This is not apparent until the repair is completed. Also, if an ignition coil/module ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders mis-firing. Inspect the ground circuit for the ignition coil/modules on the cylinder bank of the engine that has more than one cylinder mis-firing. |
| • | 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. |
| • | For an intermittent condition, refer to Symptoms . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Misfire current counters will not increment if certain DTCs set at the same time or after DTC P0300 sets. Refer to Conditions for running DTC P0300 for applicable DTC list.
If more than one cylinder is misfiring, the Misfire current counters may increment for only 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.
Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look/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 concern, 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.
-
The cylinder with the more significant misfire may cause another cylinders counter to increment only by a small amount.
-
If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
-
If you cannot find any fuel system conditions, go to Engine Mechanical. An engine mechanical condition can cause a spark plug to gas foul. Inspect for loose rockers, collapsed lifters or worn camshaft lobes. Refer to Engine Mechanical.
-
If the customers concern is the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic. Refer to DTC P0420 Catalyst System Low Efficiency Bank 1 and/or DTC P0430 Catalyst System Low Efficiency Bank 2 .
Step | Action | Value(s) | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||||||||
|
Important: If any DTCs are set, refer to those DTCs before proceeding with this diagnostic.
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/physically inspect the following items:
Did any of the above tests isolate a condition requiring a repair? | -- | ||||||||||||||||||||||
6 |
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? | 700ohms | ||||||||||||||||||||||
9 |
Does the spark plug appear to be OK? | -- | ||||||||||||||||||||||
Important: If the Injector Coil Test Procedure does not isolate the condition, go to Engine Mechanical. Did the misfire move with the spark plug? | -- | |||||||||||||||||||||||
11 | Are the spark plugs oil or coolant fouled. | -- | Go to Engine Mechanical | |||||||||||||||||||||
|
Important: If the Fuel System Diagnosis does not isolate the condition, go to Engine Mechanical. Are the spark plugs gas fouled? | -- | Go to Fuel System Diagnosis | ||||||||||||||||||||||
13 |
Important: If the Injector Coil Test Procedure does not isolate the condition, go to Engine Mechanical. Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | ||||||||||||||||||||||
14 | Replace or re-gap spark plugs. If improper gap is found, be sure to re-gap spark plugs using a wire type gauge, J 41319. Refer to Spark Plug Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||||||||||||||
15 | Replace the faulty spark plug(s). Refer to Spark Plug Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||||||||||||||
16 | Replace the faulty ignition wire(s). Refer to Spark Plug Wire Harness Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||||||||||||||
Was the customers concern that the MIL was flashing? | -- | Go to DTC P0420 Catalyst System Low Efficiency Bank 1 and/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 |
