GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon XL - 2WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 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 to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for 3-way catalytic converter overheating are present.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0128, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P1114, P1115, P1120, P1220, P1258, or P1336 are not set.
    • The engine speed is between 450-5,000 RPM.
    • The ignition voltage is between 10-18 volts.
    • The engine coolant temperature (ECT) is between -7 to +130°C (19-266°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 traction control systems are not active.
    • The transmission is not changing gears.
    • The secondary air injection (AIR) diagnostic test is not in progress (RPO NC1 only)
    • The A/C clutch is not changing states.
    • The PCM is not in fuel shut-off or decel fuel cut-off mode.
    • The ABS signal is not exceeding rough road thresholds.

Conditions for Setting the DTC
    • The PCM determines that an emission type misfire is present.
    • The PCM determines that a catalyst damaging misfire is present.

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
    • Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have fuel level DTCs also set.
    •  Water contamination in the fuel system can cause a single cylinder to misfire as well as cause a random misfire. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis .
    • Excessive vibration from sources other than the engine could cause a misfire DTC. The following are possible sources of vibration:
       - Variable thickness brake rotor
       - Drive shaft not balanced
       - Certain rough road conditions
    • Observe if more than one cylinder is misfiring, the scan tool may only display one cylinder misfiring. This will not be apparent until the repair is completed. If an ignition coil ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders misfiring. Inspect the ground circuit for the ignition coil on the cylinder bank of the engine that has more then one cylinder misfiring.
    • Perform the following procedures to diagnosis conditions that may be causing the misfire counter to increment:
       - Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.
       - If the Misfire Current counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. Perform the diagnostic table for DTC P0335 first if this condition is suspected.
       - If a misfire is present and you suspect a fuel control problem, force the fuel system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to Engine Controls Scan Tool Data List.
       - A misfire may not be apparent at idle. The misfire may only occur above idle under a load. Road test the vehicle and monitor the misfire current counters.
       - If more than one cylinder is misfiring, the misfire current counters may only increment for one cylinder. Example: Cylinders 1 and 8 are both misfiring, yet only cylinder 8 increments on the misfire current counter.
       - If one of the injector fuses is open, only 2 or 3 misfire current counters may increment for the corresponding side of the engine.

Test Description

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

  1. This step diagnoses the conditions that are causing the misfire counter to increment.

    2.

  2. The cylinder with the more significant misfire may cause another cylinder counter to increment only by a small amount.

    3.

  3. If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.

    4.

  4. An engine mechanical problem can cause a spark plug to gas foul. Inspect for loose rockers, collapsed lifters, or worn camshaft lobes.

    5.

  5. If the customer concern is the MIL flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.

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 CKP system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .
   • If any DTCs other than DTC P0135 or DTC P0155 are set, refer to those DTCs before proceeding with this diagnostic.
   • If any abnormal engine mechanical noise can be heard, refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises or Base Engine Misfire with Abnormal Valve Train Noise in Engine Mechanical.

  1. Install the scan tool.
  2. Idle the engine.
  3. Monitor all the Misfire Current counters on the misfire data list using a scan tool. There are a total of 8 counters, 1 counter per cylinder.

Are any of the Misfire Current counters incrementing?

--

Go to Step 4

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Start the engine.
  5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
  6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, and then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

Is only one misfire counter incrementing?

--

Go to Step 6

Go to Step 5

5

Inspect the following components:

    • Vacuum hoses for splits, kinks, and proper connection--Refer to Emission Hose Routing Diagram .
    • Throttle body and intake manifold for vacuum leaks
    • Crankcase ventilation valve or system for vacuum leaks.
    • The PCM grounds for being clean and secure--Refer to Ground Distribution Schematics in Wiring Systems.
    • The ignition coil ground circuit for an open on the cylinders that are showing misfires--An open ground causes all 4 ignition coils to be inoperative. The Misfire current counters only displays 2-3 cylinders misfiring, not all 4 cylinders.
    • All injector harness connectors that are connected to the proper injector
    • The injector and ignition control fuses for being open--If you find an open fuse, locate and repair the shorted circuit. Refer to Wiring Repairs in Wiring Systems.
    • Incorrect fuel pressure or restricted fuel flow--Refer to Fuel System Diagnosis .
    • A restricted exhaust--Refer to Restricted Exhaust in Engine Exhaust.
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Abnormal engine mechanical noises--Refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises or Base Engine Misfire with Abnormal Valve Train Noise in Engine Mechanical.

Did any of the above checks isolate a condition requiring a repair?

--

Go to Step 17

Go to Step 6

6
  1. Turn OFF the ignition.

    2. Important: Before disconnecting the injector harness, refer to Fuel Injection Fuel Rail Assembly Replacement . There is a special procedure for disconnecting the fuel injector harness connectors.

  2. Disconnect the injector that corresponds to the Misfire Current counters that were incrementing.
  3. Connect the J 34730-2C injector test lamp to the injector electrical connector.
  4. Idle the engine.

Is the injector test lamp flashing?

--

Go to Step 7

Go to DTC P0200

7
  1. Turn OFF the ignition.
  2. Reconnect the injector harness electrical connector.
  3. Disconnect the ignition wires from the spark plug that corresponds to the Misfire Current counters that were incrementing. Refer to Spark Plug Wire Replacement .
  4. Install the J 26792 Spark Tester to a ground.
  5. Start the engine.

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

--

Go to Step 9

Go to Step 8

8
  1. Remove the ignition wire for the cylinder that is misfiring. Refer to Spark Plug Wire Replacement .
  2. Measure the resistance of the ignition wire using the DMM.

Is the ignition wire resistance less than the specified resistance?

700 ohms

Go to Electronic Ignition (EI) System Diagnosis

Go to Step 16

9
  1. Remove the spark plugs from the cylinder that indicated a misfire.
  2. Inspect the spark plugs. Refer to Spark Plug Inspection .

Does the spark plug appear to be OK?

--

Go to Step 10

Go to Step 11

10

    Important:  If the Injector Coil Test checks to be OK, refer to the appropriate base engine misfire diagnostic procedures.

  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 15

Go to Fuel Injector Solenoid Coil Test

11

Are the spark plugs oil or coolant fouled?

--

Go to Symptoms - Engine Mechanical

Go to Step 12

12

Important:  If the fuel system checks to be OK, refer to the appropriate base engine misfire diagnostic procedures.

Are the spark plugs gas fouled?

--

Go to Fuel System Diagnosis

Go to Step 13

13

Important:  If the Injector Coil Test checks to be OK, refer to appropriate base engine misfire diagnostic procedures.

Do the spark plugs show any signs of being cracked, worn, or improperly gapped?

--

Go to Step 14

Go to Fuel Injector Solenoid Coil Test

14

Replace or re-gap spark plugs. Refer to Spark Plug Replacement . If an improper gap is found, be sure to re-gap spark plugs using a wire type gauge.

Is the action complete?

--

Go to Step 17

--

15

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

Is the action complete?

--

Go to Step 17

--

16

Replace the faulty ignition wires. Refer to Spark Plug Wire Replacement .

Is the action complete?

--

Go to Step 17

--

17

If the customers concern that the MIL was flashing, were DTC P0420 or DTC P0430 set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 18

18
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 19

Go to Step 2

19

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK