Is It Safe to Drive With a P0304 Code?
Common Symptoms of a P0304 Fault
Rough or uneven idle
Hesitation under acceleration
EML on or flashing
Loss of power
Fuel smell from exhaust
Possible Causes of P0304
A P0304 code can be triggered by faults in several different vehicle systems. Identifying the specific root cause requires proper diagnostic equipment and live data analysis — not just reading the code itself.
Ignition System — Cylinder 4
Ignition component on cylinder 4 not delivering consistent spark.
Fuel Delivery — Cylinder 4
Fuel not reaching cylinder 4 reliably.
Compression Issue — Cylinder 4
Mechanical condition affecting cylinder 4.
Wiring / Connector Fault
Electrical fault on the cylinder 4 circuit.
Why we don't list the exact part: A P0304 code tells you what's happening but not why. Replacing parts based on the code alone without proper diagnosis is the most common way drivers waste money. A proper diagnosis identifies the exact cause first.
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P0304 and Your MOT
A stored P0304 fault code will cause your car to fail its MOT. The engine management light will be illuminated during the test, which is an automatic failure under current MOT testing standards. Even if the light clears temporarily, the code remains in the ECU memory and can be read by the tester's equipment.
Get the fault properly diagnosed and repaired first — then have the code cleared and confirm the light doesn't return before booking your test.