P0304 on Saab
Cylinder 4 Misfire Detected
P0304 on Saab vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 2 Saab models — most commonly on 9-3, 9-5. This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. Typical repair costs on Saab range from $80 to $600, depending on the specific model and root cause.
Common Causes of P0304
- •Worn or fouled spark plug in cylinder 4
- •Failed or weak ignition coil on cylinder 4
- •Faulty spark plug wire or boot (where applicable)
- •Clogged, stuck or leaking fuel injector for cylinder 4
- •Vacuum or intake air leak near that cylinder
- •Low compression (worn rings, burnt/leaking valve, head gasket)
- •Damaged wiring or connector at the coil or injector
P0304 on Saab by Model
Saab 9-3(1 issue)
- 9-3 Direct Ignition Cassette (DIC) Failure1999-2011
The Saab Direct Ignition Cassette — single integrated unit covering all four spark plugs — is a well-known wear item across 9-3 (and 9-5) from 1999 through end of production. Symptoms: misfire (often cylinder-specific then random), reduced power, check engine light. Failure rate climbs sharply after 80,000 miles. Saab DIC heat-shielding cracks; rubber boots fail.
Saab 9-5(2 issues)
- 9-5 Direct Ignition Cassette (DIC) Failure1999-2009
Same DIC failure mode as 9-3 — 1999-2009 9-5 with the B235 2.3L turbo (Linear/Arc/Vector NA variants are B205) suffers DIC degradation. Saab dealers used to stock these by the dozen. Often the first part to fail on a high-mileage 9-5.
- Direct Ignition Cassette (DIC) Failure1999-2009
The Direct Ignition Cassette, which sits directly on top of the spark plugs and combines the coils into one unit, is a frequent failure point on the four-cylinder cars. Underhood heat and valve-cover gasket oil leaks contaminating the coil pack degrade the cassette over time, causing misfires, rough idle, hard starting and stalling. A failed cassette typically has a burnt smell and discoloration around the plug boots.
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View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on Saab?▼
P0304 stands for "Cylinder 4 Misfire Detected." This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. On Saab specifically, this code is documented across 2 models.
What causes P0304 on Saab vehicles?▼
Common causes on Saab: Worn or fouled spark plug in cylinder 4, Failed or weak ignition coil on cylinder 4, Faulty spark plug wire or boot (where applicable), Clogged, stuck or leaking fuel injector for cylinder 4, Vacuum or intake air leak near that cylinder. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0304 on a Saab?▼
Repair costs on Saab range from $80 to $600, depending on the specific model and root cause.
Which Saab models have P0304 documented?▼
Au7o has documented P0304 on 2 Saab models: 9-3, 9-5.