P0300
DTC P0300 Engine Misfire Detected
System Description
The Powertrain Control Module (PCM) monitors both the crankshaft and camshaft position in order to detect engine misfire. The PCM looks for the rapid decrease in crankshaft speed associated with engine misfire once every 100 camshaft revolutions. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under severe misfire, the PCM flashes the MIL. A flashing MIL signals that a misfire capable of damaging the catalytic converter is detected. The Torque Converter Clutch is disabled momentarily to determine if the misfire was due to a rough road condition (automatic transmission only).
Conditions for Running the DTC
- No active MAP DTC's
- No active IAT DTC's
- No active ECT DTC's
- No active TP DTC's
- No active Oxygen Sensor DTC's
- No active Fuel Trim DTC's
- No active KS DTC's
- No active CKP DTC's
- No active CMP DTC's
- No active VSS DTC's
- No active IAC DTC's
- No active PCM Memory DTC's
- The engine speed is between 469 RPM and 5900 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 more than 5 seconds.
- The Fuel Level is more than 10 percent.
Conditions for Setting the DTC
The misfire total is more than 8 counts.
Action Taken When the DTC Sets
The Malfunction Indicator Lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles when there is misfire.
OR
The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
OR
- The MIL will illuminate immediately and flash if a misfire is severe enough to cause catalyst damage.
- The Torque Converter Clutch (TCC) will disable whenever a misfire is being detected with or without a misfire DTC set (automatic transmission only).
- The PCM will record the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- A scan tool can clear the DTCs.
Diagnostic Aids
An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel.
Whenever the DTC is an intermittent, refer to Symptoms.
Perform the fuel Injector Balance Test.
Steps 1 - 6:
Steps 7 - 11:
Steps 12 - 16:
Steps 17 - 20:
Steps 21 - 22:
Steps 23 - 26:
Steps 27 - 31:
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. This information on the scan tool can be referred to later.
3. A visual/physical inspection should include checking the following components:
- The wiring for proper connections, pinches or 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.
5. When all the accumulators indicate misfire, then the misfire is being caused by something that affects the entire engine.
6. If the misfire is not present, operate the vehicle within the conditions recorded in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. Whenever the misfire accumulators start to increment, then misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared.
8. Check the fuel for contamination (water, alcohol, etc).
10. Tests the ignition system voltage output using a spark tester.
11. Replace any spark plugs that are worn, cracked or fouled.
12. Checks for voltage at the ignition feed circuit.
14. A basic engine problem that affects all cylinders is the only possibility at this point (e.g. cam timing, throttle body leak, restricted air flow, etc.).
18. Whenever the fuel injector driver circuit is shorted to ground, the light will be ON steady. When the driver circuit is shorted to voltage or open, the light will be OFF.
19. Since the voltage is supplied to the fuel injector on a single circuit, the malfunction may only be a poor electrical connection or an open in the fuel injector electrical harness. An open before the harness may result in a Cranks But Will Not Run complaint.
27. The replacement PCM must be programmed and the crankshaft position system variation learn procedure must be performed. Refer to the latest Techline procedures for PCM programming.