Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

2: If the actual CKP variation values are not within the learned values, the misfire counters may increment.
3: DTC P0135 or P0155 can be set because of a misfire.

DTC P0300

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 CKP System Variation Learn Procedure . Start the engine. Allow the engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. 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	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 crankcase ventilation system for vacuum leaks-Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical. The 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 (Without Special Tool)Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Did you find and correct the condition?	-	Go to Step 20	Go to Step 8
8	IMPORTANT: An erratic or inconsistent spark is considered a no spark. Turn OFF the ignition. Disconnect the spark plug wire 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. Start the engine. Does the spark jump the tester gap?	-	Go to Step 10	Go to Step 9
9	Remove the spark plug wire for the affected cylinders. Refer to Spark Plug Wire Replacement . Inspect the spark plug wire. Refer to Spark Plug Wire Inspection . Measure the resistance of the spark plug wire with a DMM. Is the spark plug wire resistance less than the specified value?	700 Ω	Go to Electronic Ignition (EI) System Diagnosis	Go to Step 19
10	Remove the spark plugs from the cylinders that indicated a misfire. Refer to Spark Plug Replacement . Inspect the spark plugs. Refer to Spark Plug Inspection . Does the spark plug appear to be OK?	-	Go to Step 11	Go to Step 12
11	Exchange the suspected spark plug with 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 18	Go to Step 15
12	Is the spark plug oil or coolant fouled?	-	Go to Symptoms - Engine Mechanical	Go to Step 13
13	Is the spark plug gas fouled?	-	Go to Step 16	Go to Step 14
14	Did 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 Coil Test . Did you find and correct the condition?	-	Go to Step 20	Go to Symptoms - Engine Mechanical
16	Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition?	-	Go to Step 20	Go to Symptoms - Engine Mechanical
17	Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action?	-	Go to Step 20	-
18	Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement?	-	Go to Step 20	-
19	Replace the faulty spark plug wires. Refer to Spark Plug Wire Replacement . Did you complete the replacement?	-	Go to Step 20	-
20	Was the customer concern the MIL flashing?	-	Go to Step 21	Go to Step 22
21	Operate the vehicle at the specified value for 4 minutes. Operate the vehicle within the Conditions for Running the DTC P0420 or P0430 as specified in the supporting text. Refer to DTC P0420 or P0430 . Does the DTC run and pass?	2500 RPM	Go to Step 22	Go to DTC P0420 or P0430
22	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. 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 23
23	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