GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 Seville 🢒 Engine 🢒 Engine Electrical 🢒 DTC P0300

System Description

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0218, P0335, P0336, P0340, P0341, P0385, P0386, P0502, P0503, P0713, P1114, P1115, P1121, P1122, P1258, P1372 are not set.
    • The engine speed is between 500-5,850 RPM.
    • The ignition voltage is between 9-18 volts.
    • The engine coolant temperature (ECT) is between -7 and +120°C (+19 and +248°F).
    • If the start-up ECT is below -7°C (19°F), then the test is delayed until the ECT is more than 21°C (70°F).
    • The fuel level is more than 10 percent.
    • The throttle position (TP) sensor angle is steady within 1 percent.
    • The antilock brake system (ABS) and the traction control system are not active.
    • The transmission is not changing gears.
    • The A/C clutch is not changing states.
    • The PCM is not in fuel shut-off or decel fuel cut-off mode.
    • The PCM is not receiving a rough road signal.

Conditions for Setting the DTC

The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:
       - Variable thickness brake rotors--Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes.
       - Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical in Engine Mechanical.
    • If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank. Refer to Engine Controls Schematics .

Test Description

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

  1. If the actual CKP variation values are not within the learned values, the misfire counters may increment.

    2.

  2. DTC P0135 or P0155 can be set because of a misfire.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: You must perform the crankshaft position (CKP) system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .

  1. Start the engine.
  2. Allow the engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records.
  3. Monitor all of the Misfire counters with the scan tool.

Are any of the Misfire Current counters incrementing?

--

Go to Step 3

Go to Diagnostic Aids

3

Are any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4

Can any abnormal engine noise be heard?

--

Go to Symptoms - Engine Mechanical in Engine Mechanical

Go to Step 5

5

Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are below the specified value?

200 mV

Go to DTC P0131 or P0151

Go to Step 6

6

Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are fixed above the specified value?

900 mV

Go to DTC P0132 or P0152

Go to Step 7

7

Inspect the following components:

    • The vacuum hoses and seals for splits, restrictions, and improper connections--Refer to Emission Hose Routing Diagram .
    • The throttle body and intake manifold for vacuum leaks
    • The exhaust gas recirculation (EGR) system components for vacuum leaks or excessive flow--Refer to Exhaust Gas Recirculation (EGR) System Cleaning .
    • The crankcase ventilation system for vacuum leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical.
    • The powertrain control module (PCM) grounds for corrosion and loose connections--Refer to Ground Distribution Schematics in Wiring Systems.
    • The exhaust system for restrictions--Refer to Restricted Exhaust in Engine Exhaust.
    • The fuel for contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Remove the fuel pump relay. Refer to Relay Replacement in Wiring Systems.

    3. Important: DO NOT remove the connector from the ignition control (IC) module assembly.

  3. Remove the affected IC module assembly. Refer to Ignition Coil Replacement - Bank 1 or Ignition Coil Replacement - Bank 2 .

    4. Important: Not grounding the IC module assembly may cause erratic spark.

  4. Connect a jumper wire between the IC module assembly and a good ground.
  5. Install the J 36012-A Ignition System Diagnosis Harness.
  6. Install a J 26792 Spark Tester on the affected cylinder spark plug jumper wire.
  7. Crank the engine with the remaining spark plug jumper wires connected.

Does the spark tester spark?

--

Go to Step 10

Go to Step 9

9

Inspect the affected cylinder spark plug boot for missing or damaged ignition coil spring.

Did you find and correct the condition?

--

Go to Step 19

Go to Electronic Ignition (EI) System Diagnosis

10
  1. Remove the spark plug from the cylinder that indicated a misfire.
  2. Inspect the spark plug. Refer to Spark Plug Inspection .

Does the spark plug appear to be OK?

--

Go to Step 11

Go to Step 12

11
  1. Exchange the suspected spark plug with another cylinder that is operating properly. Refer to Spark Plug Replacement .
  2. Operate the vehicle under the same conditions that the misfire occurred.

Did the misfire move with the spark plug?

--

Go to Step 18

Go to Step 15

12

Is the spark plug oil or coolant fouled?

--

Go to Symptoms - Engine Mechanical in Engine Mechanical

Go to Step 13

13

Is the spark plug gas fouled?

--

Go to Step 16

Go to Step 14

14

Does the spark plug show any signs of being cracked, worn, or improperly gapped?

--

Go to Step 17

Go to Step 15

15

Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test .

Did you find and correct the condition?

--

Go to Step 19

Go to Symptoms - Engine Mechanical in Engine Mechanical

16

Perform the fuel system diagnosis. Refer to Fuel System Diagnosis .

Did you find and correct the condition?

--

Go to Step 19

Go to Symptoms - Engine Mechanical in Engine Mechanical

17

Replace or gap the spark plug. Refer to Spark Plug Replacement .

Did you complete the action?

--

Go to Step 19

--

18

Replace the faulty spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?

--

Go to Step 19

--

19

Was the customer concern the malfunction indicator lamp (MIL) flashing?

--

Go to Step 20

Go to Step 22

20
  1. Operate the vehicle at the specified value for 4 minutes.
  2. Operate the vehicle within the Conditions for Running the DTC P0420 as specified in the supporting text. Refer to DTC P0420 .

Does the DTC run and pass?

2,500 RPM

Go to Step 21

Go to DTC P0420

21
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 22

22

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK