DTC P0300 Engine Misfire Detected. Cadillac Eldorado 2000

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2000 🢒 Eldorado 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 DTC P0300 Engine Misfire Detected

Circuit Description

The crankshaft position (CKP) sensors send pulses to the PCM as the slots in the reluctor rotate past each sensor. From a correlation of the CKP pulses, the PCM calculates a reference pulse. The PCM uses the reference pulse to detect an engine misfire. The PCM calculates the time period between each pulse, and monitors the time to detect a change in the speed of the crankshaft. The PCM allows for a certain amount of crankshaft speed variation. However, when the change is more than an expected amount, the PCM will interpret the change as a misfire. If 2 percent or more of all cylinder firing events are misfires, emission levels may exceed the mandated standards. The PCM monitors misfire in blocks of data. Each block consists of 200 engine revolutions. The PCM counts the number of misfires occurring in each block. If the number of misfires exceeds the calibrated amount in a specific number of blocks, DTC P0300 will set.

Conditions for Running the DTC

•	No VSS, TP, MAP, ECT, CKP, CMP, MAF sensor, IC, or Transmission DTCs set

•	Engine speed is between 500-5850 RPM.

•	System voltage is between 9-18 volts.

•	The ECT indicates an engine temperature between -7°C (19°F) and 120°C (248°F).

If start-up ECT is below -7°C (19°F), then the test is delayed until ECT is more than 21°C (70°F).

•	Throttle angle steady.

•	A/C compressor clutch steady.

•	EGR flow test is inactive.

•	Fuel Level is above 10 percent

•	DFCO and Torque Management not active.

Conditions for Setting the DTC

5 out of 16 consecutive 200 revolution blocks containing 22 or more misfires is considered non- catalyst damaging misfire.

Any 200 revolution block containing an excessive amount of misfires (above a predetermined threshold) is considered catalyst damaging misfire.

Action Taken When the DTC Sets

•	If the misfire level is non-catalyst damaging, the PCM will illuminate 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 will immediately flash the MIL while the misfire remains at catalyst damaging levels.

•	The PCM will disable TCC operation.

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

Any data previously stored in Freeze Frame will be overwritten when this DTC sets. The only exception to this is if a fuel trim DTC was already recorded in Freeze Frame. In this case, the fuel trim data stays in Freeze Frame and the Misfire Data will be stored in Failure Records.

Conditions for Clearing the MIL/DTC

•	The PCM will turn the MIL off after three consecutive trips that the diagnostic has been run and passed.

Note that if the last failure was during a non-typical driving condition, the MIL may remain on longer than three drive trips. Review Freeze Frame for the last failure conditions.

•	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 Clear DTC Information function.

Diagnostic Aids

Check for the following conditions:

•	Incorrect CKP System Variation data stored in the PCM. Run the Crankshaft Position System Variation Learn using the scan tool.

•	System Grounds -- Ensure all connections are clean and properly tightened.

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

•	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 .

•	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) .

•	Contaminated Fuel -- Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•

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 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 failure records data for DTC P0300. If the 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 engine coolant temperatures below 80°C (176°F), the condition described above is very likely the cause of the DTC P0300 being 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.

•

Running the vehicle low on fuel -- This DTC may set if the vehicle misfires while running out of fuel. If no misfire is currently present, but the History Counters indicate random misfire was once present, ask if the vehicle has been run out of fuel. If this is the case, no further repair may be necessary.

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

If the condition is intermittent, refer to Intermittent Conditions in Symptoms.

Test Description

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

Engine misfire can change engine load characteristics which may affect the TP sensor performance diagnostic. Correct any misfire before diagnosing DTC P0121. A malfunctioning injector circuit, crankshaft position system variation not learned, an intermittent CKP sensor problem, incorrect rough road data from the EBCM, etc. may cause a misfire DTC to be set. If any other DTCs are set with DTC P0300 (except P0121), diagnose and repair the other DTC before using the DTC P0300 table.

The Misfire Bar Graph (or 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.

Certain mechanical conditions may cause the PCM to detect a misfire, but you will not be able feel or hear the engine misfiring.

Certain conditions will cause more than one cylinder to misfire.

If the customer's concern is the MIL is flashing, this indicates that a catalyst damaging misfire occurred. Operate the engine within the conditions to run DTC P0420.

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

Important:: Incorrect CKP System Variation data in the PCM may cause DTC P0300 to set with no apparent misfire. Any of the following conditions can cause incorrect CKP System Variation data:

•	Replacing the engine

•	Replacing the PCM

•	Reprogramming the PCM

•	Replacing the CKP sensor

•	Performing internal engine repairs that affect the CKP sensor to crankshaft reluctor wheel relationship.

If any of the above conditions apply to this vehicle, the CKP System Variation Learn Procedure must be performed before proceeding with misfire diagnosis. Refer to Crankshaft Position System Variation Learn .

Are any other DTCs set?

Go to Diagnostic Trouble Code (DTC) List/Type

Go to Step 3

Start the engine.
Select the Misfire Bar Graph on the scan tool (the Misfire Current counters can also be used).

Do any cylinders indicate an excessive amount of misfire?

Go to Step 5

Go to Step 4

Observe the Freeze Frame and/or the Failure records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame and/or the Failure records data that you observed.

Does the DTC fail this ignition?

Go to Step 5

Go to Diagnostic Aids

Do you feel and/or hear the engine misfiring?

Go to Step 6

Go to Step 17

Is only one cylinder misfiring?

Go to Step 11

Go to Step 7

Is an entire bank of the engine misfiring?

Go to Step 8

Go to Step 10

Turn OFF the ignition.
Disconnect the appropriate ignition control module harness connector.
Turn ON the ignition, with the engine OFF.
With a test lamp, probe between the ignition control module B+ supply circuit and the ground circuit of the ignition control module.

Does the test lamp illuminate?

Go to Step 9

Go to Secondary Ignition Diagnosis

Turn OFF the ignition.
Disconnect the appropriate ignition control module/coil assembly from the spark plugs. Refer to Ignition Control Module Replacement - Bank 1 or Ignition Control Module Replacement - Bank 2 .
Install the J 36012-A spark plug jumper wires to each spark plug and ignition coil.
Install the J 26792 spark tester to a spark plug jumper wire.
Remove the fuel injector fuses.
Connect the ignition control module harness connector.
Crank the engine and observe the spark tester.

Does a spark jump the tester gap and is the spark consistent?

Go to Base Engine Misfire Diagnosis in Engine Mechanical

Go to Secondary Ignition Diagnosis

Visually and physically inspect for the following conditions:

•	Vacuum hoses for splits, kinks and proper connections.

•	Throttle body for vacuum leaks.

•	Crankcase ventilation valve and/or system for vacuum leaks.

•	Vacuum leaks between the Intake manifold plenum and the cylinder heads.

•	Injector O-rings leaking vacuum.

•	Verify that all injector harness connectors are connected to the proper injector/cylinder.

•	Test for low fuel pressure or restricted fuel flow. Refer to Fuel System Pressure Test .

•	Inspect for a restricted exhaust. Refer to Restricted Exhaust System Check .

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

•	Ensure that the PCM ground are clean, tight, and in the proper locations.

Did you find and correct the condition?

Go to Step 19

Go to Base Engine Misfire Diagnosis in Engine Mechanical

Turn OFF the ignition.
Disconnect the appropriate ignition control module/coil assembly from the spark plugs. Refer to Ignition Control Module Replacement - Bank 1 or Ignition Control Module Replacement - Bank 2 .
Inspect the ignition coil assembly, boots and spark plug insulators for the following conditions:

•	Visible cracks, deterioration or other damage

•	Carbon tracking or other signs of arcing

•	Missing or damaged spark plug boot spring(s)

If the condition is found, repair as necessary.

Did you find and correct the condition?

Go to Step 19

Go to Step 12

Install the J 36012-A spark plug jumper wires to each spark plug and ignition coil.
Install the J 26792 spark tester to the appropriate spark plug jumper wire.
Remove the fuel injector fuses.
Crank the engine and observe the spark tester.

Does a spark jump the tester gap and is the spark consistent?

Go to Step 13

Go to Secondary Ignition Diagnosis

Turn OFF the ignition.
Remove the appropriate spark plug. Refer to Spark Plug Replacement in Engine Electrical.
Visually and physically inspect the spark plug. Refer to Spark Plug Visual Diagnosis in Engine Electrical.

Does the spark plug appear to be OK?

Go to Step 14

Go to Step 15

Swap the suspected spark plug with another cylinder that is operating correctly.
Operate the engine under the same conditions that the misfire occurred.

Important: If the Injector Coil test does not isolate the condition, refer to Base Engine Misfire Diagnosis in Engine Mechanical

Did the misfire move with the spark plug?

Go to Step 18

Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F)

Are the spark plugs oil or coolant fouled?

Go to Base Engine Misfire Diagnosis in Engine Mechanical

Go to Step 16

Important: If the fuel system diagnosis does not isolate the condition, refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Are the spark plugs gas fouled?

Go to Fuel System Pressure Test

Go to Step 18

Inspect/test for the following conditions:

•	Damaged accessory drive belt or pulley. Refer to Symptoms - Drive Belt in Engine Mechanical.

•	Damaged driven accessory (generator, water pump, drive belt tensioner, etc.). Refer to Symptoms - Drive Belt in Engine Mechanical.

•	A loose or broken engine mount. Refer to Engine Mount Inspection in Engine Mechanical.

•	Base engine mechanical condition, refer to Base Engine Misfire Diagnosis in Engine Mechanical.

•	Test for proper transaxle TCC operation.

If a condition is found, repair as necessary.

Did you find and correct the condition?

Go to Step 19

Go to Diagnostic Aids

Re-gap or replace the spark plug(s). Refer to Spark Plug Replacement in Engine Electrical.

Did you complete the repair?

Go to Step 19

Was the customer's concern that the malfunction indicator lamp (MIL) was flashing?

Go to DTC P0420 Catalyst System Low Efficiency

Go to Step 20

Observe and record the Freeze Frame data.
With a scan tool, clear the DTCs .
Turn OFF the ignition for 15 seconds.
Operate the vehicle within the Freeze Frame conditions or as closely as possible.
With a scan tool, monitor the Misfire Bar Graph.

Does the scan tool indicate a misfire?

Go to Step 2

System OK