ASE G1 Auto Maintenance and Light RepairEngine SystemsMedium
A vehicle is brought into the shop with a complaint of a rough idle, reduced engine power, and a 'Check Engine' light illuminated. A scan tool shows a P0303 diagnostic trouble code. Which of the following is the most isolated and direct cause of this specific DTC?
- AA faulty ignition coil on cylinder #3
- BA malfunctioning mass airflow (MAF) sensor
- CA clogged fuel filter supplying multiple cylinders
- DA vacuum leak affecting all cylinders
Show answer & explanationAnswer & explanation
Correct answer: A. A faulty ignition coil on cylinder #3
A P0303 code specifically indicates a misfire in cylinder #3. Among the given options, a faulty ignition coil on cylinder #3 is the most isolated and direct cause for a misfire in that particular cylinder.
Why the other options are wrong
- B. A malfunctioning MAF sensor would affect the air-fuel mixture for all cylinders, likely causing a P0300 (random/multiple misfire) or fuel trim codes, not a single-cylinder misfire.
- C. A clogged fuel filter would likely affect fuel delivery to multiple cylinders, potentially causing multiple misfire codes (P0300) or lean conditions, not just a single cylinder (P0303).
- D. A vacuum leak affecting all cylinders would typically cause a lean condition and potentially P0300 (random/multiple misfire) or fuel trim codes, not a specific single-cylinder misfire.
P030X Misfire Codes
A P030X DTC (e.g., P0301, P0302) indicates a misfire in a specific cylinder, where X represents the cylinder number. P0300 indicates a random or multiple cylinder misfire.
- P030X indicates a specific cylinder misfire.
- P0300 indicates random/multiple misfires.
- Common causes are spark, fuel, or compression issues for that cylinder.
Memory trick: P0303: Cylinder 3, a misfire's key.