System Description
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring 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 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0315, P0335, P0336, P0340, P0341, P0385, P0386, P0502, P0503, P1111, P1112, P1114, P1115, P1121, P1122, P1258, P1372 are not set. |
| • | The engine speed is between 500-6,500 RPM. |
| • | The ignition voltage is between 9-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 and +120°C (+19 and +248°F). |
| • | If the start-up ECT is below -7°C (+19°F), then the test is delayed until the ECT is more than 21°C (70°F). |
| • | The fuel level is more than 8 percent. |
| • | The throttle position (TP) sensor angle is steady within 1 percent. |
| • | The antilock brake system (ABS) and the traction control system (TCS) are not active. |
| • | The transmission is not changing gears during wide open throttle. |
| • | The PCM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The PCM is not receiving a rough road signal. |
| • | DTC P0300 runs continuous once the above conditions are met. |
Conditions for Setting the DTC
| • | The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards. |
| • | The DTC will run within 6 minutes. |
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
| • | Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration: |
| - | Variable thickness brake rotors--Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes. |
| - | Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical in Engine Mechanical. |
| • | If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil power and ground circuits for that bank. Refer to Engine Controls Schematics . |
| • | Excessive resistance in the fuel injector ignition 1 voltage circuit or the fuel injector control circuit may cause the following symptoms: |
| - | Lean condition |
| - | Misfire |
| - | Rough idle |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the actual CKP variation values are not within the learned values, the misfire counters may increment.
-
DTC P0135 or P0155 can be set because of a misfire.
Step | Action | Values | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||||||
|
Important: You must perform the crankshaft position (CKP) system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .
Are any of the Misfire Current counters incrementing? | -- | Go to Step 3 | Go to Diagnostic Aids | |||||||||||||||
Are any other DTCs set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 4 | |||||||||||||||
4 | Can any abnormal engine noise be heard? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical | Go to Step 5 | ||||||||||||||
5 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 6 | ||||||||||||||
6 |
Important: DO NOT remove the connector from the ignition control (IC) module assembly. Important: Not grounding the IC module assembly may cause erratic spark. Does the spark tester spark? | -- | Go to Step 8 | Go to Step 7 | ||||||||||||||
7 | Inspect the affected cylinder spark plug boot for missing or damaged ignition coil spring. Did you find and correct the condition? | -- | Go to Step 19 | |||||||||||||||
8 |
Does the spark plug appear to be OK? | -- | Go to Step 9 | Go to Step 10 | ||||||||||||||
9 |
Did the misfire move with the spark plug? | -- | Go to Step 16 | Go to Step 13 | ||||||||||||||
10 | Is the spark plug oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical | Go to Step 11 | ||||||||||||||
11 | Is the spark plug gas fouled? | -- | Go to Step 14 | Go to Step 12 | ||||||||||||||
12 | Does the spark plug show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 15 | Go to Step 13 | ||||||||||||||
13 | Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 17 | ||||||||||||||
14 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 19 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||||
15 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 19 | -- | ||||||||||||||
16 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||||||||||||
17 | Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are below the specified value? | 200 mV | Go to DTC P0131 or P0151 | Go to Step 18 | ||||||||||||||
18 | Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are fixed above the specified value? | 900 mV | Go to DTC P0132 or P0152 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 4.6L | ||||||||||||||
19 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 20 | Go to Step 21 | ||||||||||||||
20 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 21 | Go to DTC P0420 | ||||||||||||||
21 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 22 | ||||||||||||||
22 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
