DTC P0300 Engine Misfire Detected. Pontiac Grand Prix 2000

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2000 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0300 Engine Misfire Detected

Circuit Description

The powertrain control module (PCM) has the ability to detect a misfire by monitoring the 3X reference and the camshaft position input signals from the ignition control module. The PCM monitors the crankshaft speed variations, or reference period differences, in order to determine if a misfire is occurring. If 2 percent or more of all cylinder firing events are misfires, the emissions levels may exceed the mandated standards. The PCM determines the misfire level based on the number of misfire events monitored during a 200-engine revolution test sample. The PCM continuously tracks 16 consecutive 200-revolution test samples. If 22 or more misfires are detected during any 10 of the 16 samples, DTC P0300 will set. If the misfire is large enough to cause possible three-way catalytic converter damage, DTC P0300 may set during the first 200-revolution sample in which the misfire was detected. in the case of a catalyst-damaging misfire, the malfunction indicator lamp (MIL) will flash in order to alert the vehicle operator of potential catalyst damage.

Conditions for Running the DTC

•	The following DTCs are NOT set:

-	Vehicle speed sensor (VSS)

-	Throttle position (TP) sensor

-	Manifold absolute pressure (MAP) sensor

-	Engine coolant temperature (ECT) sensor

-	Crankshaft position (CKP) sensor

-	Camshaft position (CMP) sensor

-	Mass air flow (MAF) sensor

•	The engine speed is between 550 RPM and 5850 RPM.

•	The system voltage is between 9 volts and 18 volts.

•	The ECT indicates an engine temperature between -6°C (+21°F) and 120°C (248°F).

•	The throttle angle is steady.

Conditions for Setting the DTC

The PCM is detecting a crankshaft RPM variation, indicating a misfire that is sufficient to cause 3-way catalytic converter damage, or sufficient to cause emissions levels to exceed the mandated standard.

Action Taken When the DTC Sets

•	The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic has been run and failed unless 3-way converter damage is possible, in which case the lamp will illuminate after the first failure.

•	The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

•	The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

•	The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using a scan tool.

Diagnostic Aids

The scan tool provides information that can be used in order to identify the misfiring cylinder. If the DTC P0300 is currently stored as DTC status Failed Since Code Clear, the misfire history counters (Misfire History 1 - 6) will still contain a value that represents the level of misfire detected on each cylinder.

A misfire DTC may set if components that affect the crankshaft position sensor have recently been replaced, and the CKP System Variation Learn Procedure has not been performed. If the diagnostic table does not identify a problem then perform the Crankshaft Position System Variation Learn . If you have replaced any of the following components, or if DTC P1336 has set, perform the Crankshaft Variation Learn Procedure:

•

The PCM

•	The engine

•	The crankshaft

•	The crankshaft harmonic balancer

•	The crankshaft position sensor

The scan tool displayed misfire counter values (Misfire History 1 through 6) can help to determine whether the misfire affects a single cylinder or a cylinder pair, or if the misfire is random. If the largest amount of activity is isolated to a cylinder pair, inspect for the following conditions:

•	The secondary ignition wires--Check the secondary wires that are associated with the affected cylinder pair for disconnected ignition wires or for excessive resistance. The wires should measure under 600 ohms per/ft.

•	A damaged or malfunctioning ignition coil for the following conditions:

Cracks

-	Carbon tracking

-	Other damage

-	Coil secondary resistance--The secondary resistance should be between 5000 ohms (5 K ohms) and 8000 ohms (8K ohms).

•	Substitute a known good coil. Switch the ignition coils and retest. If the misfire follows the coil, replace the ignition coil. If the misfire is random, check for the following conditions:

-	The system grounds--Ensure that all connections are clean and properly tightened.

The mass air flow sensor (MAF) --A MAF sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Operate the vehicle within the Failure records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the Mass Airflow Sensor Replacement .

-	A damaged accessory drive belt or a damaged belt-driven accessory--A damaged serpentine belt or belt-driven accessory can cause engine load variations sufficient to set a misfire DTC.

-	The air induction system--Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for the following conditions:

•	Disconnected or damaged vacuum hoses

•	An incorrectly-installed or malfunctioning crankcase ventilation valve

•	Vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces.

-	The fuel pressure--Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test (VIN K) or to Fuel System Pressure Test (VIN 1) .

-	The fuel injectors--Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) .

-	Water contamination in the fuel system-Even small amounts of water can cause a single cylinder to misfire or cause a random misfire. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

-	The EGR system--Check for a leaking valve, adapter, or feed pipes which will contribute to a lean condition or an excessive EGR flow.

An extended idle--Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting the 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 the DTC P0300 to set, review the Freeze Frame and Failure Records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC to set. If the DTC P0300 occurs during idle or during very low engine speeds and at engine coolant temperatures below 80°C (176°F), the condition described above is very likely the cause of the DTC to set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 g/s.

Important: If the level of misfire was sufficient to cause possible catalyst damage, indicated by the MIL flashing, ensure that the DTC P0420 test is completed and passed after you verify the misfire repair.

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

•	Loose terminal connection

-	Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

•

Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

•	Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

A malfunctioning injector circuit, a crankshaft position system variation not learned condition, or incorrect rough road data from the EBCM may cause a misfire DTC to set. If any of the indicated DTCs are set with DTC P0300, diagnose and repair the other DTC before you use the DTC P0300 table.

The Misfire Current Cyl display may normally display a small amount of activity, typically 0-10 counts, but should not steadily increment during an entire 200-evolution test sample period.

Depending on the cause of the misfire, the Misfire History Cyl counter will display a very large number for the misfiring cylinders. Values for the non-misfiring cylinders will be less than 1/2 as great as the misfiring cylinders. When you investigate a misfire, always start with that conditions that are associated with the cylinders that have the largest number of counts stored in the Misfire History Cyl counter.

Steps 5-1 tests for conditions that can cause a random cylinder misfire.

Steps 13-23 test for conditions that can cause a non-random or single cylinder misfire.

DTC P0300 - Engine Misfire Detected

Step

Action

Values

Yes

Did you perform the Powertrain On Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any other DTCs set?

Go to the applicable DTCs

Go to Step 3

Start and idle the engine.
Review and record the scan tool Freeze Frame data.
Operate the vehicle within the conditions that were present when the DTC was set.
Monitor the scan tool Misfire Current Cyl display for each cylinder.

Is Misfire Current display incrementing for any cylinder, indicating that a misfire is currently occurring?

Go to Step 4

Go to Diagnostic Aids

Use a scan tool in order to view the Misfire History Cyl display.

Does Misfire History Cyl display a very large value for more than one cylinder?

Go to Step 5

Go to Step 13

Inspect the vacuum hoses for splits, for kinks, and for improper connections. Refer to Emission Hose Routing Diagram .
Repair the condition as necessary.

Did you find and correct the condition?