DTC P0300 Engine Misfire Detected. Chevrolet Monte Carlo 1998

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1998 🢒 Monte Carlo 🢒 DTC 🢒 DTC P0300 Engine Misfire Detected

Engine Controls Components
Ignition System, Knock Sensor
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The PCM has the ability to detect a misfire by monitoring the 3X reference from the Ignition Control (IC) Module and camshaft position input signals from the Camshaft Position (CMP) Sensor. The PCM monitors crankshaft speed variations (reference period differences) 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 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 MIL will flash to alert the vehicle operator of the potential of catalyst damage.

Conditions for Running the DTC

•	No TP, MAP, ECT, CKP, CMP, MAF sensor, VSS, DTCs set.

•	Engine speed between 550 and 5900 RPM.

•	System voltage between 9.0 and 16.0 volts.

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

•	Throttle angle steady.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

•	The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

•	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 MIL during the third consecutive trip in which the diagnostic has been 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 the scan tool.

Diagnostic Aids

The scan tool provides information that can be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as Test failed since code clear, the misfire history counters (Misfire Hist #1- #6) will still contain a value that represents the level of misfire for each cylinder.

A misfire DTC may set if components that affect the Crankshaft Position Sensor have recently been replaced, and the Crankshaft Position System Variation Learn has not been performed. If the diagnostic table does not identify a problem then perform the Crankshaft Position System Variation Learn . The Crankshaft Position Variation Learn Procedure should be performed if any of the following conditions are true:

•	The PCM has been replaced.

•	DTC P1336 is set.

•	The Engine has been replaced.

•	The Crankshaft has been replaced.

•	The Crankshaft Harmonic Balancer has been replaced.

•	The Crankshaft Position Sensor has been replaced.

The scan tool displayed misfire counter values (Misfire Hist. #1 through #6) can be useful in determining whether the misfire is isolated to a single cylinder or to a cylinder pair (cylinders that share an ignition coil-1/4, 2/5, 3/6.) If the largest amount of activity is isolated to a cylinder pair, check for the following conditions:

•	Secondary Ignition Wires: Check wires for affected cylinder pair for disconnected ignition wires or for excessive resistance 600ohms per foot (1 968ohms per meter).

•	Damaged Or Faulty Ignition Coil: Check for cracks, carbon tracking or other damage. Also check coil secondary resistance. Secondary resistance should be (the wires should measure under 8Kohms (8000ohms).

•	Substitute a Known Good Coil: Swap ignition coils and retest. If the misfire follows the coil, replace the ignition coil. Refer to Ignition Coil Replacement .

If the misfire is random, check for the following conditions:

•	System Grounds: Ensure all connections are clean and properly tightened. Refer to Power and Grounding Component Views in Wiring Systems.

•	MAF: A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition.

•

Air Induction System: Air leaks into the induction system which bypass the MAF sensor will cause a lean condition. Check for disconnected or damaged vacuum hoses, incorrectly installed or faulty crankcase ventilation valve, or for vacuum leaks at the throttle body, EGR valve, and intake manifold mounting surfaces. Refer to Visual/Physical Inspection in Symptoms .

•	Fuel Pressure: Perform a fuel system pressure test. Refer to Fuel System Pressure Test . A faulty fuel pump, plugged filter, or faulty fuel system pressure regulator will contribute to a lean condition.

•

Injector(s): Perform injector coil/balance test to locate faulty injector(s) contributing to a lean or flooding condition. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) , Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test . In addition to the above test, check the condition of the injector O-rings.

•	EGR: Check for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.

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 numbers below refer to the step numbers on the Diagnostic Table:

A faulty injector or injector circuit will cause a misfire DTC to be set.

The Misfire Cur # 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 counter will display a very large number for the misfiring cylinder(s), values for the non-misfiring cylinders will be less than half 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 counter.

Steps 5 through 13 check for conditions that can cause a random cylinder misfire.

Steps 14 through 16 check for injector faults using J 34730-380. While using this tool DTC P0107, P0117, P1107 and P1114 may be stored as active. This is from disconnecting the 10-way injector connector to install the tool (the MAP sensor and ECT sensor circuits also pass through this connector). Disregard these DTCs when using this tool.

Steps 17 through 25 check for conditions that can cause a non-random or single cylinder misfire.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to EEPROM Programming procedures. Refer to Powertrain Control Module Replacement/Programming .

DTC P0300 - Engine Misfire Detected

Step

Action

Value(s)

Yes

Was the Powertrain On Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any injector DTC(s) set?

Go to Applicable Injector DTC

Go to Step 3

Start and idle the engine.
Review and record scan tool Freeze Frame data.
Operate the vehicle to duplicate the conditions present when the DTC was set (as defined by the Freeze Frame data).
Monitor the scan tool Misfire Cur. # display for each cylinder.

Does Misfire Cur. # display increment for any cylinder (indicating a misfire currently occurring)?

Go to Step 4

Go to Diagnostic Aids

Does Misfire Hist. # display a very large value for more than one cylinder?

Go to Step 5

Go to Step 14

Visually and physically inspect the vacuum hoses for splits, kinks, and improper connections.
If a problem is found, repair as necessary.

Was problem found?