Circuit Description
The crankshaft position (CKP) sensor sends pulses to the powertrain control module (PCM) when the reluctor teeth rotate past the sensor. The PCM uses these pulses in order to synchronize ignition and fuel injector operation. The PCM also measures the interval between each pulse in order to determine if an excess change in the crankshaft speed has occurred. A misfire causes an unwanted change in the crankshaft speed. A certain amount of crankshaft acceleration or of deceleration is expected between each firing stroke. If the crankshaft speed changes are more than an expected amount, the PCM will interpret this as misfire. If 2 percent or more of all cylinder firing events are misfires, the emission levels may exceed the mandated standards. The PCM monitors blocks of 200 engine revolutions and counts the number of misfires in each block.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0123, P0335, P0340, P0385, P0501, P0503, P1106, P1107, P1114, P1115, P1121, P1122, or P1336 are not set. |
| • | The engine speed is between 550-5,850 RPM. |
| • | The system voltage is 9-16 volts. |
| • | The engine coolant temperature (ECT) indicates an engine coolant temperature of -6 to +120°C (21-248°F). |
| • | The throttle angle is steady. |
| • | The fuel level is more than 10 percent. |
| • | The decel fuel cutoff mode and the torque management are not active. |
Conditions for Setting the DTC
| • | Five out of 16 consecutive 200-revolution blocks that contain 22 or more misfires is considered a non-catalyst damaging misfire. |
| • | Any 200-revolution block that contains an amount of misfire above a predetermined threshold is considered a catalyst damaging misfire. |
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
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
The scan tool provides information that can be useful in identifying the misfiring cylinder. If DTC P0300 is currently stored as Failed Since Code Clear, the misfire history counters will represent the level of misfire detected on each cylinder. The misfire counter values can be useful in determining if the misfire affects a single cylinder or is random.
If the misfire is random, check for the following conditions:
| • | Any CKP system variation data that is stored in the PCM that is incorrect--Run the Crankshaft Position System Variation Learn . |
| • | A damaged accessory drive belt or a damaged belt-driven accessory--A damaged serpentine belt or a damaged belt-driven accessory can cause engine load variations sufficient to set a misfire DTC. |
| • | The air induction system--Any vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for the following conditions: |
| - | Any disconnected vacuum hoses or any damaged vacuum hoses |
| - | A positive crankcase ventilation (PCV) valve that is incorrectly installed or is malfunctioning |
| - | Any vacuum leaks at the throttle body |
| - | Any vacuum leaks at the EGR valve |
| - | Any vacuum leaks at the intake manifold mounting surfaces |
| • | The fuel pressure--Perform a fuel system pressure test. A faulty fuel pump, a restricted filter, or a faulty fuel pressure regulator will contribute to a lean condition. Refer to Fuel System Diagnosis . |
| • | The fuel injectors--Refer to Fuel Injector Solenoid Coil Test . |
| • | A contaminated fuel supply--Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | The EGR system--Check for a leak which will contribute to a lean condition or to an excess EGR flow. |
| • | An extended idle--Excess Open Loop operation that is caused by extended idling or by short trip driving may leave deposits on the heated oxygen sensors (HO2S). The deposits cause the sensors to respond slowly to the exhaust oxygen content, affecting fuel control, and causing a misfire to be indicated at idle. This condition is not permanent. In order to determine if this condition is causing DTC P0300 to set, review the Freeze Frame and the Failure Records for DTC P0300. If DTC P0300 occurs at high engine speeds, the condition that is described above did not cause the DTC to set. If the DTC occurs at low engine speeds and an ECT of less than 80°C (176°F), the condition may cause the DTC being set. The deposits on the HO2S can be eliminated by operating the warmed-up vehicle at a mass airflow of over 15 g/s. |
| • | Operating the vehicle with a low fuel level--This DTC may set if the vehicle misfires while running out of fuel. If a misfire is not present and the History Counters indicate random misfire was present, determine if the vehicle has been run out of fuel. If this is the case, further repair may not be necessary. |
Important: If the misfire was sufficient to cause catalyst damage and the MIL flashed, ensure the DTC P0420 test is passed after verifying the misfire repair.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition occurs. This may assist in diagnosing the condition.
If the concern is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Engine misfire can change the engine load characteristics which may affect the TP sensor performance diagnosis. Before diagnosing DTC P0121, correct any misfire . The following conditions may cause a misfire DTC to be set: The CKP system variation is not learned, an intermittent CKP sensor concern, incorrect rough road data from the electronic brake control module (EBCM), and/or a faulty injector circuit. Before using the DTC P0300 diagnostic table, diagnose and repair any other DTCs .
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The Misfire Current Cyl display may display a small amount of activity, but should not steadily increment during an entire test period.
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A misfiring cylinder or a non-firing cylinder can sometimes affect the misfire counters for other cylinders. When performing this diagnosis, concentrate on the cylinder with the highest level of misfire, and correct the concern. This may also correct the other cylinders that indicate misfire. This step splits the test between the conditions that would cause a specific cylinder to misfire and the conditions that would affect all cylinders.
Step | Action | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||||||||
2 |
Important:: Any CKP system variation data in the PCM that is incorrect may cause
DTC P0300 to set without obvious misfire. Any of the following conditions
can cause the CKP system variation data to be incorrect:
Was service that requires running the CKP System Variation Learn procedure performed recently? | Go to Step 3 | |||||||||||
Are any other DTCs present? | Go to Step 4 | ||||||||||||
Do any cylinders indicate an excess amount of misfire? | Go to Step 5 | Go to Diagnostic Aids | |||||||||||
Is the misfire affecting specific cylinders, not random cylinders? | Go to Step 14 | Go to Step 6 | |||||||||||
6 | Inspect the vacuum hoses for splits, for kinks, and for incorrect connections. Refer to Emission Hose Routing Diagram . Did you find and correct the condition? | Go to Step 19 | Go to Step 7 | ||||||||||
7 | Inspect the PCV valve for incorrect installation and for any damaged O-rings. Did you find and correct the condition? | Go to Step 19 | Go to Step 8 | ||||||||||
8 | Inspect the throttle body inlet and the duct work for damage and for objects that may alter the air flow through the MAF sensor. Did you find and correct the condition? | Go to Step 19 | Go to Step 9 | ||||||||||
9 | Check the fuel pressure. Refer to Fuel System Diagnosis . Did you find and correct the condition? | Go to Step 19 | Go to Step 10 | ||||||||||
10 | Check the fuel for excess water, for alcohol, and for other contaminants. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Did you find and correct the condition? | Go to Step 19 | Go to Step 11 | ||||||||||
11 | Verify that the PCM grounds and the ignition control module grounds are clean, tight, and in the correct locations. Refer to Power Distribution Schematics in Wiring Systems. Did you find and correct the condition? | Go to Step 19 | Go to Step 12 | ||||||||||
12 | Inspect the following areas for any vacuum leaks:
Did you find and correct the condition? | Go to Step 19 | Go to Step 13 | ||||||||||
13 |
Did you find and correct the condition? | Go to Step 19 | Go to Step 14 | ||||||||||
14 | Check for correct ignition system operation. Refer to Electronic Ignition (EI) System Diagnosis . Did you find and correct the condition? | Go to Step 19 | Go to Step 15 | ||||||||||
15 | Check for correct fuel injector operation. Refer to Fuel Injector Balance Test with Tech 2 . Did you find and correct the condition? | Go to Step 19 | Go to Step 16 | ||||||||||
16 | Check for vacuum leaks that may affect one cylinder more than other cylinders. Possible causes include the following conditions:
Did you find and correct the condition? | Go to Step 19 | Go to Step 17 | ||||||||||
17 | Check for the following mechanical concerns:
Did you find and correct the condition? | Go to Step 19 | Go to Step 18 | ||||||||||
18 |
Did you find and correct the condition? | Go to Step 19 | Go to Diagnostic Aids | ||||||||||
19 |
Does the DTC run and pass? | Go to Step 20 | Go to Step 3 | ||||||||||
20 | With a scan tool, observe the stored information, Captured Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK |
