DTC P0300 Engine Misfire Detected. Buick Skylark 1998

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1998 🢒 Skylark 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 DTC P0300 Engine Misfire Detected

Engine Controls Components
Ignition Controls
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

System Description

The Powertrain Control Module (PCM) monitors both the crankshaft and the camshaft position in order to detect an engine misfire. A rapid decrease in the crankshaft speed indicates misfire. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and before illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under a severe misfire, the PCM flashes the MIL. A flashing MIL indicates that there is a misfire that is capable of damaging the catalytic converter. The torque converter clutch (TCC) disables momentarily in order to determine if the misfire was due to a rough road condition, automatic transmission only.

Conditions for Setting the DTC

•	The misfire total is greater than 12 counts.

•	The engine speed is between 469 RPM and 6400 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 15 seconds.

•	The Throttle Position (TP) hasn't changed more than 8% in 1 second.

•	DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0404, P0405, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, P1404, and P1621 not set.

Action Taken When the DTC Sets

•	The malfunction indicator lamp (MIL) illuminates if the fault is active within the same conditions for two out of eighty ignition cycles and a misfire is present.

The MIL illuminates after two consecutive ignition cycles during in which the diagnostic runs with the fault active

The MIL illuminates immediately and flashes if a misfire is severe enough to cause any catalyst damage.

•	In vehicles with automatic transmission only, the torque converter clutch (TCC) is disablesd when a misfire is present.

•	The PCM records the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

•	A history DTC is stored.

•	The coolant fan turns ON.

Conditions for Clearing the MIL/DTC

•	The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed.

•	A history DTC clears after 40 consecutive warm up cycles without a fault.

•	Clear the MIL/DTCs with a scan tool.

Diagnostic Aids

An intermittent can also be the result of a defective reluctor wheel. Remove crankshaft sensor and inspect reluctor wheel through sensor mount hole. Check for porosity and condition of wheel.

Verify the electronic Ignition Control Module (ICM) 11 pin harness connector terminal K, ground circuit should have less than 0.5 ohms of resistance.

If DTC is intermittent, refer to Symptoms .

When checking the electrical terminal connections with a test light or DMM, a malfunctioning electrical terminal connection maybe cleaned and not detected as a problem. You may also clean a corroded or dirty electrical terminal connection when disconnecting and reconnecting any electrical connector.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

The Powertrain OBD System Check prompts the technician to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

If a DTC P0200 is present, the condition causing the misfire is in the fuel injector circuitry. The DTC P0200 table will diagnose the fuel injectors and the fuel injectors circuitry.

A visual/physical inspection should include checking the following components:

•	The ignition systems electrical wiring for the following condition(s):

-	Proper electrical terminal connections

-	Pinches in the wires

-	Cuts in the wires

•	The PCM grounds for being clean and tight

•	The vacuum hoses for proper connections as shown on the Vehicle Emission Information label

•	Check the Intake manifold sealing surfaces for air leaks

•	Check the EGR valve for the following conditions:

-	Air leaks in the EGR tubes

-	Stuck open

-	Loose bolts at mounting plate

-	Poor mounting gasket

This step determines if the DTC P0300 is the result of a hard malfunction or an intermittent condition.

If the misfire is not present, it may be necessary to duplicate the conditions in the freeze frame data in order to detect the misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. If the misfire accumulators start to increment, then this indicates that the misfire is present. A sudden change in the throttle, a rough road, or other crankshaft rotation disturbances may cause the counter to increment a few counts and then stop. This can be considered normal and should not be diagnosed as a misfire. The history counter begins counting after the DTC is set and will indicate only true misfires. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared.

If all of the accumulators indicate misfire, then the misfire is being caused by something that affects the entire engine.

A basic engine problem or a fuel injector problem that affects all of the cylinders is possible at this point (e.g. the valve train, the compression, etc.). Refer to Base Engine Misfire Diagnosis in Engine Mechanical for the diagnosis. Also refer to DTC P0200 Injector Control Circuit .

After repairs, verify a no misfire by duplicating the conditions within Freeze Frame Data while watching the misfire counters.

Important: If the fused jumper wire is not used to ground the ICM assembly, the system may spark erratically.

If a spark plug boot is burned, the other spark plug on that ignition coil may still fire at idle. This step tests the systems ability to produce at least 25,000 volts at each spark plug.

Refer to Spark Plug Replacement in Engine Electrical.

Replace any spark plugs that are in the following condition:

•

Worn

•

Cracked

•

Fouled

No spark on one coil may be caused by an open secondary circuit. Therefore, the coils secondary resistance should be checked. If the resistance readings are above 20,000 ohms, but not infinite, this will probably not cause a no start but may cause an engine miss under certain conditions.

The test light will blink if the no spark condition is caused by the following items:

•	Ignition coil electrical connections

•	Ignition coil

•	Secondary boot assembly

Thoroughly check any suspected circuitry for the following conditions:

•	Backed out terminals

•	Improper mating

•	Broken locks

•	Improperly formed or damaged terminals

•	Poor terminal to wiring connections

•	Physical damage to the wiring harness

Program the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline procedure for PCM reprogramming and to Crankshaft Position System Variation Learn .

Conditions for setting the DTC P0420 need to be performed in order to determine that the catalyst has been damaged from the 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

Turn ON the ignition switch leaving the engine OFF.
Install a scan tool.

Was a DTC P0200 set?

Go to DTC P0200 Injector Control Circuit

Go to Step 3

Turn OFF the ignition switch.
Perform a visual/physical inspection. Refer to the Symptoms for the visual/physical inspection procedure.
Make any repairs that are necessary.

Were any repairs necessary?

Go to Step 28

Go to Step 4

Start the engine.
Idle the engine.
Observe the Misfire Current Counters with the scan tool.

Are there any Misfire Current counters incrementing?

Go to Step 6

Go to Step 5

Turn OFF the engine leaving the ignition switch ON.
Review the Freeze Frame data and record the parameters.
Start the engine.
Operate the vehicle within the Conditions For Setting the DTC as specified.

Are there any Misfire Current counters incrementing?

Go to Step 6

Go to Step 28

Was misfire present in all cylinders?

Go to Step 7

Go to Step 11

Turn OFF the ignition switch.
Install a fuel pressure gauge. Refer to step 2 of the Fuel System Diagnosis for the fuel pump gauge installation procedure.
Start the engine.
Observe the fuel pressure with the engine running.

Is the fuel pressure within the specified range?

290-379kPa (42-55psi)

Go to Step 8

Go to Fuel System Diagnosis

Turn OFF the ignition switch.
Check the fuel for the following conditions: Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•

Water

•

Alcohol

•	Other contamination

Is the fuel OK (uncontaminated)?

Go to Step 9

Go to Step 10

Check for a fuel injector problem. Refer to DTC P0200 Injector Control Circuit starting at step 3.
Check for a basic engine problem. Refer to the Base Engine Misfire Diagnosis in Engine Mechanical for the diagnostic procedure.

Is the action complete?

Go to Step 28

Replace the contaminated fuel. Refer to the Fuel System Cleaning .

Is the action complete?

Go to Step 28

Turn OFF the ignition switch.
Remove the air cleaner outlet resonator. Refer to the Air Cleaner Outlet Resonator Replacement for the removal procedure.
Disconnect all the fuel injector electrical connectors.
Disconnect the ICM 11 pin electrical connector.
Temporarily remove the ignition coil and electronic Ignition Control Module (ICM) assembly.
Reconnect the ICM 11 pin electrical connector.

Important: If the fused jumper wire is not used to ground the ICM assembly, the system may spark erratically.

Install a fused jumper wire between the ICM assembly to ground.
Install the J 36012-A spark plug jumper wires.
Install the J 26792 spark plug tester on the #1 spark plug jumper wire.
Remove the spark plug boot assembly from the #4 (companion of #1) cylinder of the ignition coil housing.
Install a jumper wire from the #4 (companion of #1) spark plug connector of the ignition coil housing to ground.
Crank the engine with the remaining spark plug wires still connected.
Repeat the above steps on 1-4 and 2-3 of the spark plug jumper wires until all the spark plug jumper wires have been checked for spark. Making sure the companion cylinder is grounded.

Does the spark tester spark on all of the cylinders?

Go to Step 12

Go to Step 13

Turn OFF the ignition switch.
Check for any malfunctioning spark plugs in the cylinders that indicated a misfire. Refer to Spark Plug Visual Diagnosis in Engine Electrical.
Replace the malfunctioning spark plugs if necessary. Refer to Spark Plug Replacement in Engine Electrical.

Were any spark plugs malfunctioning?

Go to Step 28

Go to Step 9

Turn OFF the ignition switch.
Disconnect the PCM electrical connector (C1).
Reconnect theJ 26792 spark tester on a plug wire that did not show spark.
Remove the spark boot assembly from the companion cylinder.
Connect a jumper wire to the companion cylinder spark plug connector of the ignition coil housing to ground.
Turn ON the ignition switch leaving the engine OFF.
Connect a test light to B+.

Notice: Do not leave the test lamp connected to the PCM IC circuit connector for longer than 5 seconds at a time. Failure to do so may damage the ignition coil and/or the Ignition Control Module.

Momentarily touch the affected IC circuit at the PCM electrical connector (C1-25 or C1-26). A spark should be present when the test light is removed from the IC circuit.

Is there a spark present when you remove the test light from the IC circuit?

Go to Step 25

Go to Step 14

Turn OFF the ignition switch.
Remove the spark plug boot assemblies from the affected coil at the ignition coil housing.
Connect a DMM between the secondary ignition coil terminals (spark plug connectors 1-4 or 2-3) at the ignition coil housing.

Is the resistance between the specified values?

4-8Kohms

Go to Step 15

Go to Step 16

Remove the ignition coil housing from the cover.
Disconnect the ignition coil harness electrical connector at the ICM.
Connect another test light to B+.
Probe the ignition coil control terminal that did not have spark at the ICM with the test light.
Turn ON the ignition switch leaving the engine OFF.

Notice: Do not leave the test lamp connected to the PCM IC circuit connector for longer than 5 seconds at a time. Failure to do so may damage the ignition coil and/or the Ignition Control Module.

Again, momentarily touch the affected IC circuit at the PCM electrical connector (C1-25 or C1-26) with the test light while watching the other test light.

Does the other test light blink?

Go to Step 17

Go to Step 18

Remove the ignition coil housing.
Disconnect the ignition coil electrical connector from the ICM.
Remove the ignition coil from the ignition coil housing.
Recheck the resistance between the secondary terminals of the ignition coils.

Is the resistance between the specified values?

4-8Kohms

Go to Step 20

Go to Step 22

Turn OFF the ignition switch.
Check the coil control circuit between the ICM and the ignition coils for the following conditions:

•	Open circuit

•	Short to ground

•	Poor electrical terminal connections at the ignition coils or the ICM

•	Short to ignition coil voltage

Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 28

Go to Step 19

Turn OFF the ignition switch.
Disconnect the ICM 11 pin electrical connector.
Check the affected IC input circuit between the ICM and the PCM for the following condition(s):

•	Open circuit

•	Short to ground

•	Short to voltage

Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 28

Go to Step 24

Remove the ignition coils from the ignition coil housing.
Disconnect the ignition coil electrical connector from the ignition coils.
Reconnect the ignition coil electrical connector to the ICM.
Connect a test light to ground.

Important: Carefully handle the ignition coils electrical connectors to avoid spark arching from the electrical terminals and causing the IGN fuse to open which would lead to misdiagnosis.

Turn ON the ignition switch leaving the engine OFF.
Probe the ignition feed circuit to the ignition coils at both of the ignition coil electrical connector terminals B with the test light.

Does the test light illuminate for both circuits?

Go to Step 20

Go to Step 23

Inspect the following items for corrosion and/or damage for the affected cylinder(s):

•	Spark plug boot assemblies

•	The ignition coil springs

•	The ignition coil housing

Replace the components as necessary.

Was a repair necessary?

Go to Step 28

Go to Step 21

Check the spark plug boot assembly.
Repair or replace the spark plug boot assembly as necessary.

Was a repair or replacement necessary?

Go to Step 28

Go to Step 22

Check the PCM electrical terminal connections for poor connection(s).
If the PCM electrical terminal connections are OK, then replace the affected ignition coil. Refer to Ignition Coil Replacement .

Is the action complete?

Go to Step 28

Turn OFF the ignition switch.
Repair the open in the ignition feed circuit between the #1-4 and #2-3 ignition coils electrical connectors. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 28

Replace the ICM. Refer to Ignition Control Module Replacement .

Is the action complete?

Go to Step 28