Test Description

The number below refers to the step number on the diagnostic table.

2: If the actual crankshaft position (CKP) variation values are not within the learned values, the misfire counters may increment.

DTC P0300

Step	Action	Values	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle
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 . 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 Current 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 - Vehicle	Go to Step 4
4	Can any abnormal engine noise be heard?	-	Go to Symptoms - Engine Mechanical	Go to Step 5
5	Observe the Misfire History Cyl# parameter with a scan tool. Does more than one cylinder indicate a large count value for the Misfire History Cyl# parameter?	-	Go to Step 6	Go to Step 8
6	Are the Misfire History Cyl# counts indicated for companion cylinders 1/4 or 2/5 or 3/6?	-	Go to Step 8	Go to Step 7
7	Inspect the following components: The vacuum hoses and seals for splits, restrictions, and improper connections-Refer to Evaporative Emissions 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 . The exhaust gas recirculation (EGR) system components for vacuum leaks or excessive flow-Refer to Exhaust Gas Recirculation (EGR) System Cleaning . The powertrain control module (PCM) grounds for corrosion and loose connections-Refer to Ground Distribution Schematics . The Exhaust System for restrictions-Refer to Restricted Exhaust . The fuel for contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Did you find and correct the condition?	-	Go to Step 20	Go to Step 8
8	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 to a good ground. See Special Tools . Jumper the spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil. Start the engine. Does the spark jump the tester gap, and is the spark consistent?	-	Go to Step 10	Go to Step 9
9	Remove the spark plug wire for the affected cylinder. 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. Refer to Ignition System Specifications . Is the spark plug wire resistance less than or equal to the specified resistance?	-	Go to Electronic Ignition (EI) System Diagnosis	Go to Step 19
10	Remove the spark plug from the cylinder that indicated a misfire. Inspect the spark plug. Refer to Spark Plug Wire 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	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 Diagnosis (w/J39021 or w/Tech 2) or Fuel Injector Diagnosis (w/CH47976) . 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 replacement?	-	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 malfunction indicator lamp (MIL) flashing?	-	Go to Step 21	Go to Step 22
21	Operate the vehicle at the specified value for 4 minutes. If the customer concern is the MIL flashing, operate the vehicle within the Conditions for Running the DTC P0420 as specified in the supporting text. Refer to Diagnostic Trouble Code (DTC) List - Vehicle . Do the DTCs run and pass?	2,500 RPM	Go to Step 22	Go to Diagnostic Trouble Code (DTC) List - Vehicle
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	In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the conditions for running and setting DTC P0420 and verify that P0420 runs and passes. Refer to DTC P0420 . Does the DTC run and pass?	-	Go to Step 24	Go to DTC P0420
24	Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	System OK