Test Description

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

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

2: If the actual 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-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 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 DTCs other than P0300 or P0136 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	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 Emission Hose Routing Diagram . The throttle body and intake manifold for vacuum leaks The crankcase ventilation system for vacuum leaks-Refer to in Engine Mechanical. 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 in Wiring Systems. The exhaust for restrictions-Refer to Restricted Exhaust in Engine Exhaust. The fuel for contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) . 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. 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. Is the spark plug wire resistance less than the specified resistance?	700 Ω	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 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 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 Coil Test . Did you find and correct the condition?	-	Go to Step 20	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 20	Go to Symptoms - Engine Mechanical in 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. 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 22	Go to DTC P0420
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