DTC P0300 Engine Misfire Detected. Oldsmobile Intrigue 1999

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 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 camshaft position (CMP) input signals from the ignition control module (ICM). The PCM monitors crankshaft speed variations (reference period differences) in order to determine if a misfire is occurring. If 2% or more of all cylinder firing events are misfires, emission levels may exceed mandated standards. The PCM determines misfire level based upon 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 5 of the 16 samples, DTC P0300 is set. If the misfire is large enough to cause possible 3-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) flashes in order to alert the vehicle operator of the potential of catalyst damage.

Conditions for Running the DTC

None of the following DTCs are set:

•	Vehicle speed sensor (VSS) DTCs

•	Throttle position (TP) sensor DTCs

•	Manifold absolute pressure (MAP) sensor DTCs

•	Engine coolant temperature (ECT) sensor DTCs

•	Camshaft position (CMP) sensor DTCs

•	Crankshaft position (CKP) sensor DTCs

•	Mass air flow (MAF) sensor DTCs

The engine speed is between 550 and 5850 RPM.
The system voltage is between 9 and 16 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 sufficient to cause 3-way catalytic converter damage, or emissions levels to exceed mandated standards.

Action Taken When the DTC Sets

•	If the misfire level is non-catalyst damaging, the PCM illuminates the MIL during the second key cycle in which the DTC sets.

•	If the misfire is severe enough to cause possible catalyst damage, the PCM immediately flashes the MIL while the misfire remains at catalyst damaging levels.

•	The PCM disables TCC operation.

•	The PCM stores the conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

•	The PCM turns the MIL off during the third consecutive trip in which the diagnostic has run and passed.

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

•	The DTC may be cleared using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

The scan tool provides information that may be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as DTC status Failed Since Code Clear, the misfire history counters (Misfire Hist #1 - #6) still contain a value that represents the level of misfire detected on each cylinder. The scan tool displayed misfire counter values (Misfire Hist. #1 through #6) may be useful in determining whether the misfire affects a single cylinder, a cylinder pair (cylinders that share an ignition coil - 1/4, 2/5, 3/6), or is random. If the largest amount of activity is isolated to a cylinder pair, inspect for the following conditions:

•	Test the secondary wires associated with the affected cylinder pair for disconnected ignition wires or for excessive resistance. The resistance should measure under 7,000 ohms.

•	Inspect for a damaged or malfunctioning ignition coil. Look for cracks, carbon tracking, or other damage. Also measure the coil secondary resistance. The secondary resistance should be between 5000 ohms and 8000 ohms.

•	Substitute a known good ignition coil and retest. If the misfire follows the coil, replace the ignition coil.

If the misfire is random, inspect or test for the following conditions

•	Ensure that all of the system ground connections are clean and properly tightened.

•

A MAF sensor output that causes the PCM to sense a lower than normal air flow causes a lean condition. Try operating the vehicle within the fail records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor. Refer to Mass Airflow Sensor Replacement .

•	A damaged serpentine belt or belt driven accessory may cause engine load variations sufficient to set a misfire DTC.

•

Inspect the air induction system. Vacuum leaks that cause intake air to bypass the MAF sensor cause a lean condition. Inspect for disconnected or damaged vacuum hoses, an incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces.

•	Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator contribute to a lean condition.

Refer to Fuel System Pressure Test .

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

•	Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•	Inspect the EGR system for a leaking valve, adapter, or feed pipes which may contribute to a lean condition or excessive EGR flow.

•

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 fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at an ECT below 80°C (176°F), the condition described above is very likely the cause of DTC P0300 being set. The deposits on the heated oxygen sensors may be eliminated by operating the fully warm vehicle at mass air flows above 15 g/s.

Important: If the level of misfire is sufficient to cause possible catalyst damage, ensure that the DTC P0420 test is completed and passed after verifying the misfire repair.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

The number(s) below refer to the step number(s) on the Diagnostic Table.

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

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

Depending on the cause of the misfire, the Misfire History Cyl # counter will display a very large number for the misfiring cylinder(s); values for the non-misfiring cylinders will be less than 1/2 as great as the misfiring cylinder(s). When investigating a misfire, always start with items associated with the cylinder(s) that has the largest number of counts stored in the Misfire History Cyl # counter.

Steps 5 through 12 check for conditions that can cause a random cylinder misfire.

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

DTC P0300 - Engine Misfire Detected

Step

Action

Value(s)

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 also set?

Go to applicable DTCs first.

Go to Step 3

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

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

Go to Step 4

Go to Diagnostic Aids

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

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

Go to Step 5

Go to Step 13

Visually and physically inspect the vacuum hoses for splits, kinks, and improper connections. Refer to Emission Hose Routing Diagram .
If a problem is found, repair as necessary.

Was a problem found?