GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Prizm 🢒 DTC 🢒 DTC P0304 Cylinder 4 Misfire Detected

Refer to Engine Controls Schematics

Ignition System


Object Number: 624329 Size: FS
Engine Controls Components
CMP and CKP Sensors
Main Power Feed
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Cell 10: Ignition Switch, IGN Fuse, and ST Fuse
Cell 14: G105 and G106 (1 of 2)
 and to

Fuel Injectors
Object Number: 624333 Size: FS
Engine Controls Components
Engine Data Sensors (1 of 2)
Fuel Supply System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Cell 10: Ignition Switch, IGN Fuse, and ST Fuse
 .

Circuit Description

The powertrain control module (PCM) uses the crankshaft position (CKP) sensor and camshaft position (CMP) sensor to determine engine misfire. The CKP sensor and the CMP sensor monitor the respective components and evaluate changes in the crankshaft rotational speed for each cylinder. Irregular changes in the crankshaft rotational speed indicate a possible misfire. The malfunction indicator lamp (MIL) illuminates when the misfire rate equals or exceeds a pre-determined count. A misfire rate that is high enough can cause the catalytic converter to overheat under certain driving conditions. The MIL will flash on and off when the conditions for catalytic converter overheating are present. Each cylinder is monitored individually for a misfire condition.

Conditions for Running the DTC
    • The engine speed is between 200 and 4,000 RPM.
    • The battery voltage is between 9 volts and 17 volts.
    • The engine coolant temperature is between -7°C (20°F) and 123°C (254°F).

Conditions for Setting the DTC

A misfire is indicated in cylinder 4.

Action Taken When the DTC Sets
    • The PCM flashes the malfunction indicator lamp (MIL) the first time catalytic converter damage can occur.
    • The PCM illuminates the MIL the second time emission thresholds are exceeded (second time the diagnostic fails).
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. The PCM also freezes the engine speed at Misfire and the Load at Misfire scan tool data parameters at the time the MIL illuminates.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
    • A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.
    • A DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

Check for any of the following conditions:

    • If any DTCs other than misfire (P0300 to P0304) are present, diagnose those DTCs first.
    • An intermittent ignition system malfunction may cause a DTC P0304 to set. Check the ignition system performance with an engine oscilloscope.
    • The engine speed at Misfire and the Load at Misfire scan tool data parameters are fixed at the time the MIL illuminates. These scan tool displays can be used like additional lines of Freeze Frame data. Review the engine speed at Misfire and the Load at Misfire scan tool parameters located on the scan tool Engine Data list. The information can help determine the vehicle conditions when the misfire occurred.
    • Review the misfire counters located in the Engine Data list of the scan tool while the engine is running. If the Total Misfire Current data parameter is increasing, the misfire condition is present. A current DTC P0304 should indicate misfire activity in the Misfire Current Cyl #4 parameter. Use this information in order to determine if the fault is present now, or is an intermittent malfunction.
    • An intermittent can also be the result of a defective CKP sensor signal rotor. Remove the CKP sensor and inspect the signal rotor through the sensor hole. Check the condition of the signal rotor for nicks, dents, missing teeth, and foreign material.
    • Check for engine overheating.
    • A MAF sensor output that is incorrect may cause the PCM to command the fuel system to go lean. Check the performance of the MAF sensor. If the HO2S voltage is fixed low, while the fuel trim is constantly high, check the MAF sensor signal circuit for resistance. High circuit resistance can cause the sensor to read a lower volume of air than actual, resulting in a lean fueling condition that can cause engine misfire.
    • Check for a PCV system malfunction. Perform a functional check of the PCV valve. Refer to Crankcase Ventilation System Inspection .

An intermittent malfunction may be caused by a fault in the cylinder 4 ignition system or fuel system electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

Test Description

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

  1. The OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step verifies whether the misfire is present. The scan tool will display increasing counts in the Misfire Current Cyl. #4 parameter if a misfire in cylinder 4 is occurring.

    3.

  3. This step checks whether the DTC P0304 is the result of a hard failure or an intermittent condition. Operating the vehicle in Check mode enhances the diagnostic capabilities of the PCM. For additional information on Check mode operation, refer to the Powertrain Control Module Diagnosis. The scan tool will display increasing counts in the Misfire Current Cyl. #4 parameter if a misfire in cylinder 4 is occurring.

    4.

  4. Fault not present indicates that the condition that caused the DTC P0304 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent DTC P0304.

    5.

  5. This step is to verify if the misfire is cause by a fault in the ignition system.

    6.

  6. Contaminants in the fuel, such as alcohol or water, can create a misfire condition.

    7.

  7. A vacuum leak can cause a lean misfire condition.

Step

Action

Values

Yes

No

1

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install a scan tool.
  2. Start the engine.
  3. Monitor the Misfire Current Cyl. #4 parameter on the scan tool.

Did the scan tool indicate a misfire in cylinder 4?

--

Go to Step 5

Go to Step 3

3

  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check mode, using the scan tool.
  3. Operate the vehicle within the Freeze Frame conditions as specified.
  4. Monitor the Misfire Current Cyl. #4 parameter on the scan tool.

Was a DTC P0304 set or did the scan tool indicate a misfire in cylinder 4?

--

Go to Step 5

Go to Step 4

4

The fault is not present.

Are there any DTCs stored that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Diagnostic Aids

5

Are DTCs P1300, P1305, P1310, or P1315 present?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 6

6
  1. Disconnect the cylinder 4 ignition coil electrical connector.
  2. Remove the cylinder 4 ignition coil. Refer to Ignition Coil Replacement .
  3. Connect the cylinder 4 ignition coil electrical connector.
  4. Install a J 26792 spark tester or an equivalent at the end of cylinder 4 ignition coil boot.
  5. Crank the engine while observing the spark tester.
  6. A crisp, blue spark should be observed.

Was a crisp, blue spark present on every engine revolution?

--

Go to Step 8

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Swap the ignition coil. Replace the suspected faulty ignition coil of cylinder 4 with an ignition coil from a normally operating cylinder.
  3. Install the J 26792 spark tester or an equivalent at the end of the ignition coil boot.
  4. Test for spark as performed in step 6.

Did the test indicate a crisp, blue spark while cranking the engine?

--

Go to Step 15

Go to Step 16

8
  1. Perform a visual/physical inspection of the cylinder 4 ignition coil boot and spark plug for the following conditions:
    2. • Water intrusion
    • A corroded or a poor connection to the spark plug
    • Carbon tracking
  2. Repair the condition or replace the ignition coil or spark plug as necessary. Refer to Ignition Coil Replacement or to Spark Plug Replacement .

Was a repair necessary?

--

Go to Step 18

Go to Step 9

9
  1. Remove the cylinder 4 spark plug. Refer to Spark Plug Replacement .
  2. Visually and physically inspect the spark plug for any of the following conditions:
    3. • Any oil fouling
    • Any fuel fouling
    • Any evidence of coolant in the cylinder
    • An incorrect gap
    • A loose center electrode
    • A cracked porcelain
    • Any carbon tracking
    • A loose terminal end
  3. Repair or replace as necessary.

Was a faulty spark plug condition found and repaired?

--

Go to Step 18

Go to Step 10

10
  1. Turn OFF the engine.
  2. Disconnect the cylinder 4 fuel injector electrical connector.
  3. Install a J 34730-2B fuel injector test lamp or an equivalent into the fuel injector harness connector.
  4. Observe the fuel injector test lamp while cranking the engine.

Does the injector test lamp blink while cranking the engine?

--

Go to Step 11

Go to Fuel Injector Circuit Diagnosis

11

Perform the Fuel Injector Coil Test and the Fuel Injector Balance Test procedures. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and to Fuel Injector Balance Test .

Did any fuel injectors require replacement?

--

Go to Step 18

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Install a fuel pressure gauge. Refer to Fuel Pressure Gage Installation and Removal .
  4. Install a scan tool.
  5. Turn ON the ignition, with the engine OFF.
  6. Select Fuel Pump in the Engine Output Controls menu of the scan tool.
  7. Turn ON the fuel pump, using the scan tool.
  8. Observe the fuel pressure indicated by the fuel pressure gauge with the fuel pump running.

Is the fuel pressure within the specified range?

301-347 kPa (44-50 psi)

Go to Step 13

Go to Fuel System Diagnosis

13

  1. Check a fuel sample for the following concerns:
    2. • Any alcohol or other contamination, refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • The fuel type and quality
  2. Replace the fuel as necessary.

Was a repair necessary?

--

Go to Step 18

Go to Step 14

14

  1. Visually and physically inspect the following for vacuum leaks:
    2. • The PCV valve
    • The intake manifold gasket
    • The vacuum lines, hoses, and fittings
  2. Repair any vacuum leaks as necessary.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

15

Replace the cylinder 4 ignition coil. Refer to Ignition Coil Replacement .

Is the action complete?

--

Go to Step 18

--

16
  1. Inspect the cylinder 4 ignition coil circuits for the following conditions:
    2. • An open in the ignition coil ground circuit
    • An open in the positive voltage supply circuit
    • An open in the trigger signal circuit
    • No trigger signal generated by the PCM
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems or to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 18

--

17
  1. Check for any of the following engine mechanical concerns:
    2. • A worn or faulty camshaft
    • A leaky or sticky valve
    • Excessive valve deposits
    • Weak valve springs
    • A faulty valve lifter
    • An intake manifold runner leak or obstruction
    • Broken or worn piston rings
    • A leaking head gasket
  2. Repair as necessary. Refer to Engine Compression Test in Engine Mechanical.

Was a basic engine mechanical concern found and repaired?

--

Go to Step 18

Go to Diagnostic Aids

18
  1. Perform the scan tool Clear DTC Information function.
  2. Operate the vehicle within the Freeze Frame conditions that set the DTC.
  3. Monitor the Misfire Current Cyl. #4 parameter on the scan tool.

Did a DTC set or did the scan tool indicate a misfire in cylinder 4?

--

Go to Diagnostic Trouble Code (DTC) List

System OK