DTC P0300. GMC Truck Yukon

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 DTC P0300

Circuit Description

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the 3-way catalytic converter. The malfunction indicator lamp (MIL) will flash if converter damaging conditions are present.

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0128, P0335, P0336, P0341, P0343, P0502, P0503, P1114, P1115, P1120, P1220, P1221, or P1336 are not set.

•	The engine speed is between 375 RPM and 5,001 RPM for automatic transmission.

•	The engine speed is between 450 RPM and 5,001 RPM for manual transmission.

•	The ignition voltage is between 10 volts and 18 volts.

•	The ECT is between -7°C (19°F) to +130°C (+266°F).

•	The fuel level is more than 10 percent.

•	The 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 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.

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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

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Verify that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

•	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.

•	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 can 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 then one cylinder is misfiring, the scan tool may only display one cylinder misfiring. This will not be apparent until the repair is completed. Also, 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.

Test Description

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

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 the Engine 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 two or three misfire current counters may increment for the corresponding side of the engine.

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

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

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

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.

DTC P0300 - Engine Misfire Detected

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

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 P0135 and P0155 are set, refer to those DTCs before proceeding with this diagnosis.

•	If any abnormal engine mechanical noise can be heard, refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises in Engine Mechanical 4.8L, 5.3L, 6.0L.

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

Are any of the Misfire Current counters incrementing?

Go to Step 4

Go to Step 3

Turn ON the ignition, leaving the engine OFF.
Review the Freeze Frame/Failure Records data for this DTC.
Turn OFF the ignition for 15 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC, and as closely as possible to the Freeze Frame/Failure Records conditions.
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

Is only one misfire counter incrementing?

Go to Step 6

Go to Step 5

Inspect the following items:

•	Observe the HO2S readings on the scan tool. If the signal is fixed below mV, refer to DTC P0131 or P0151 . If the signal is fixed above 900 mV, refer to DTC P0132 or P0152 .

•	Inspect the vacuum hoses for splits, kinks, and the correct connections. Refer to Emission Hose Routing Diagram .

•	Inspect throttle body and the intake manifold for vacuum leaks.

•	Inspect the crankcase ventilation system for any vacuum leaks .

•	Verify the PCM grounds are clean and secure. Refer to Ground Distribution Schematics in Wiring Systems.

•	Inspect 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 display 2-3 cylinders misfiring, not all four cylinders.

•	Verify that all of the injector harness connectors are connected to the proper injector

•	Inspect the injector fuses and the ignition control fuses. If you find an open fuse, locate and repair the short circuit. Refer to Wiring Repairs in Wiring Systems.

•	Test for incorrect fuel pressure and for a restricted fuel flow. Refer to Fuel System Diagnosis .

•	Inspect for a restricted exhaust. Refer to Restricted Exhaust in Engine Exhaust.

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

•	Refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises in Engine Mechanical 4.8L, 5.3L, 6.0L if an abnormal engine mechanical noise is heard.

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

Go to Step 17

Go to Step 6

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.

Turn OFF the ignition.
Disconnect the injector that corresponds to the Misfire Current counters that were incrementing.
Connect the injector test lamp to the injector electrical connector.
Idle the engine.

Does the injector test lamp flash?

Go to Step 7

Go to DTC P0200

Turn OFF the ignition.
Connect the injector harness electrical connector.
Disconnect the ignition wires from the spark plug that corresponds to the Misfire Current counters that were incrementing. Refer to Spark Plug Wire Replacement .
Install the J 26792 spark tester to a ground.
Start the engine.

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

Go to Step 9

Go to Step 8

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

Is the resistance less than the specified value?

700 ohms

Go to Electronic Ignition (EI) System Diagnosis

Go to Step 16

Remove the spark plugs from the cylinder that indicated a misfire. Refer to Spark Plug Replacement .

Does the spark plug appear to be OK?

Go to Step 10

Go to Step 11

Important: If the Injector Coil Test Procedure is OK, refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises in Engine Mechanical 4.8L, 5.3L, 6.0L.

Switch the suspected spark plug with the spark plug from another cylinder that is operating properly. Refer to Spark Plug Replacement .
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

Are the spark plugs oil fouled or coolant fouled?

Go to Base Engine Misfire with Abnormal Internal Lower Engine Noises in Engine Mechanical 4.8L, 5.3L, 6.0L

Go to Step 12

Important: If the fuel system is OK, refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises in Engine Mechanical 4.8L, 5.3L, 6.0L.

Are the spark plugs gas fouled?

Go to Fuel System Diagnosis

Go to Step 13

Important: If the Injector Coil Test Procedure is OK, refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises in Engine Mechanical 4.8L, 5.3L, 6.0L.

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

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

Is the action complete?

Go to Step 17

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

Is the action complete?

Go to Step 17

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

Is the action complete?

Go to Step 17

If the customer's concern is that the MIL was flashing, are any catalyst DTCs set?

Go to DTC P0420 or P0430

Go to Step 18

Use the scan tool in order to clear the DTCs.
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.

Does the DTC run and pass?

Go to Step 19

Go to Step 2

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