Ram-specific code — factory diagnostic data| DTC Data Sheet | |
| Code | P0303 |
| Vehicle | Ram 1500 (2009-2024) |
| Engine | 5.7L V8 HEMI (Eagle, with MDS) |
| System | IGNITION SYSTEM |
| Fault type | Performance |
| Official meaning | Cylinder 3 Misfire Detected |
Definition source: Ram factory description. Diagnostic guidance is based on factory-defined fault logic for this code.
Decode any Ram 1500 VIN — free recalls, specs & safety ratings — free VIN decoder with NHTSA data
Looking for the cross-vehicle definition? Read the generic P0303 article for the SAE-defined fault logic that applies to all manufacturers.
P0303 Quick Answer
P0303 on a Ram 1500 means the PCM detected misfires localized to cylinder 3 (passenger bank, front of engine). Cylinder 3 is NOT an MDS-deactivated cylinder on the Hemi (MDS controls cylinders 1, 4, 6, 7) — so this is almost always an ignition or fuel issue specific to cylinder 3: aging spark plugs (both plugs, since the Hemi runs two per cylinder), a failing coil pack, or a fuel injector problem. Plug change is the first-step fix.
What Does P0303 Mean on a Ram 1500?
The Ram 1500 (2009-2024) stores P0303 when the condition described above is met. This guide focuses on the 5.7L V8 HEMI (Eagle, with MDS) — the most common Ram 1500 powertrain. The platform-specific failure patterns documented below differ from the generic SAE definition.
Symptoms
- Rough idle, especially cold
- Hesitation under acceleration
- P0303 specific code, sometimes paired with P0300
- Flashing CEL under load = severe misfire, do not drive
- Loss of fuel economy
- Possible exhaust smell from raw fuel
Common Causes (Most Likely on This Model First)
- Worn or fouled spark plugs (cyl 3). Hemi has 16 plugs — two per cylinder. By 60-70k miles real-world (less than the 100k spec) the plugs need replacement. Always replace all 16 at once, never just two on one cylinder.
- Failing ignition coil on cyl 3. COP coils fail one at a time. Swap the coil to a clean cylinder; if misfire follows, replace it.
- Un-seated coil boot after plug service. Common mistake — boot doesn’t click home after recent plug change. Pull and re-seat.
- Fuel injector failure on cyl 3. Clogged or stuck-closed injector. Pull live data and watch fuel correction per cylinder, or pull and bench-test the injector.
- Compression loss on cyl 3. Less common but verify if plugs/coils/injectors check good. Compression test on cyl 3 vs. neighbors.
Diagnostic Approach
- Read freeze frame — note RPM and load at fault. Idle-only = ignition; load-only = fuel pressure / injector.
- Pull the two spark plugs on cylinder 3 (passenger side, second from front). Look for wet/oily fouling, light grey (correct), white (lean), or carbon-fouled black.
- Swap the cylinder 3 coil with a clean cylinder coil. Clear codes, drive. If misfire follows the coil, replace it.
- Verify both coil boots on cylinder 3 are firmly seated.
- If plugs and coil are good, listen for the injector clicking on cyl 3 (use a long screwdriver or stethoscope). Silent injector = electrical or mechanical failure.
- Compression test on cyl 3 if all electrical checks clean. Should be within 10% of neighboring cylinders.
Possible Fixes
| Fix | When |
|---|---|
| Replace all 16 spark plugs (set) | Plugs over 60k miles, fouled |
| Replace cyl 3 ignition coil | Misfire follows the coil when swapped |
| Re-seat coil boot | Loose boot found after inspection |
| Replace cyl 3 fuel injector | Injector electrically dead or stuck |
| Compression repair (top end work) | Compression test fails on cyl 3 |
Can I Still Drive With P0303?
Steady CEL: drive carefully to a shop. Flashing CEL: stop immediately — severe misfire dumps unburnt fuel into the catalyst and can destroy the substrate in 15-30 minutes.
How Serious Is This Code?
Moderate. A single bad coil or plug isn’t catastrophic; persistent severe misfire damages the cat. Compression issues escalate fastest.
Repair Costs
| Repair | Cost |
|---|---|
| Spark plug replacement (all 16) | $340 – $580 |
| Single ignition coil | $95 – $180 |
| Fuel injector replacement (single) | $280 – $580 |
| Top end repair (head, valves) | $2,400 – $4,800 |
FAQ
Where is cylinder 3 on a Ram 1500 Hemi?
On the 5.7L Hemi V8, cylinder 3 is on the passenger bank, second from the front. Cylinders are numbered 1-3-5-7 (driver side, front to rear) and 2-4-6-8 (passenger side, front to rear). Cylinder 3 is also NOT an MDS-deactivated cylinder (those are 1, 4, 6, 7).
What causes a P0303 on a Ram 1500?
On the Hemi, the leading causes are: aging spark plugs (replace all 16 at once), a failing ignition coil on cylinder 3, a loose coil boot after recent plug service, or a failing fuel injector on that cylinder.
Can I drive my Ram with P0303?
Steady CEL: yes, briefly. Flashing CEL: no — get it towed. A flashing light means severe ongoing misfire that destroys the catalytic converter in less than half an hour of driving.
How much does P0303 cost to fix on a Ram?
Spark plug replacement (all 16): $340-$580. Single coil: $95-$180. Single injector: $280-$580. Top-end repair if compression-related: $2,400-$4,800. Most P0303 cases resolve with plugs or a coil.