P0300

Misfire - Related Circuits:

System Description
The Powertrain Control Module (PCM) monitors crankshaft and camshaft position to detect if the engine is misfiring. The PCM looks for a sudden drop in crankshaft speed. This test is executed in blocks of 100 camshaft revolution tests. It may take several tests to store a DTC and illuminate the Malfunction Indicator Lamp (MIL). Under light misfire conditions, it may also take more than one trip to set a DTC. Severe misfire will flash the MIL indicating that catalytic converter damage is possible.

Conditions for Setting the DTC
- The misfire total is greater than or equal to 12 counts.
- The engine speed is between 469 RPM and 3400 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 for greater than 15 seconds.
- The Throttle Position (TP) angle hasn't changed more than 8% in 1 second.
- One or more of the following DTCs are not set P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0502, P0503, P0601, P1133, P1406, P1441.

Action Taken When the DTC Sets
- The 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 misfire is severe enough to cause catalyst damage.
- The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn "OFF" after three 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.
- DTCs can be cleared by using a scan tool.

Diagnostic Aids
- When DTC P0300 is intermittent, refer to "Diagnosis by Symptom."

DTC P0300 - Multiple Misfire Detected (1 Of 3):

DTC P0300 - Multiple Misfire Detected (2 Of 3):

DTC P0300 - Multiple Misfire Detected (3 Of 3):

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The 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 fault 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.
- For air leaks at the throttle body mounting area and intake manifold sealing surfaces.
4. This determines if DTC P0300 is the result of a hard fault or an intermittent condition.
5. When all the accumulators are relatively equal, then the misfire is being caused by something that affects the entire engine. When they are not then the misfire is being caused by something that is specific to two or more cylinders.
6. Whenever the misfire is not present operating the vehicle may be necessary to duplicate the conditions 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 starts 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 fuel for water, alcohol, etc.
9. A basic engine problem that effects all cylinders is the only possibility at this point. (I.e. cam timing, throttle body leak, restricted air flow, etc.)
11. Tests the harness wiring and for PCM control of the fuel injectors using injector test light J 34780-2.
13. Checks for voltage at the ignition feed circuit.
18. Whenever the 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 voltage is supplied to the fuel injector on a single circuit, the fault could only be a poor connection or open in the fuel injector harness. An open before the harness would result in a "Cranks But Will Not Run" complaint.
29. Replace any spark plugs that are worn, cracked or fouled.
31. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.