Misfire Codes: P0300-P0312 + Coil Swap Test
A misfire code tells you where to look, not what to buy. This page decodes every OBD-II misfire code from P0300 to P0312 and walks through the coil swap test that confirms whether the coil is actually the problem before you spend money on parts.
The Coil Swap Test: 6 Steps
Every mechanic uses this. Takes 10 minutes. Confirms whether the coil is the problem before you buy anything.
Confirm and note the code
Use an OBD-II scanner to confirm the misfire code. Note the cylinder number. Example: P0301 = cylinder 1. Clear the code after noting it.
Identify cylinders 1 and 2
Look up your engine's cylinder numbering. Ford V8 numbers front-to-back on each bank. Toyota/Honda V6 numbers the front bank 1-2-3, rear bank 4-5-6. See the cylinder map table below.
Swap coils (engine cold)
Remove the coil from the misfiring cylinder and the adjacent cylinder. Install the cylinder 1 coil into position 2, and cylinder 2 coil into position 1. Reconnect all connectors. You should hear a click on each connector.
Run the engine
Start the engine. Drive 5-10 minutes or run at varying RPM in the driveway for 5 minutes. The ECU needs enough runtime to detect and log a new misfire event.
Re-scan for codes
Re-scan with the OBD-II scanner. Check for active and pending codes.
Interpret the result
Code follows the coil
P0301 becomes P0302. The coil is bad. Replace it.
Code stays on original cylinder
P0301 stays P0301. The coil is fine. Test the plug, injector, or compression in cylinder 1.
No code returns
Marginal coil or loose connector. Watch for return. Likely still the coil.
P0300-P0312 Reference Table
Every code from P0300 to P0312 with cylinder mapping, likely causes, and diagnostic next steps.
| Code | Cylinder | Likely causes | Diagnostic next step |
|---|---|---|---|
| P0300 | Random | Multiple worn plugs, vacuum leak, low fuel pressure, weak coil voltage, EGR stuck open | Check all plugs, vacuum lines, fuel pressure; no specific cylinder to swap-test |
| P0301 | 1 | Coil 1, plug 1, injector 1, low compression cylinder 1 | Coil swap test: move coil 1 to cyl 2; if code becomes P0302, coil is bad |
| P0302 | 2 | Coil 2, plug 2, injector 2, low compression cylinder 2 | Coil swap test: move coil 2 to cyl 3 |
| P0303 | 3 | Coil 3, plug 3, injector 3, low compression cylinder 3 | Coil swap test: move coil 3 to cyl 4 |
| P0304 | 4 | Coil 4, plug 4, injector 4, low compression cylinder 4 | Coil swap test: move coil 4 to cyl 1 or 3 |
| P0305 | 5 (V6+) | Coil 5, plug 5, injector 5, low compression cylinder 5 | Coil swap test within same bank |
| P0306 | 6 (V6+) | Coil 6, plug 6, injector 6, low compression cylinder 6 | V6: check if rear bank (intake removal may be needed) |
| P0307 | 7 (V8+) | Coil 7, plug 7, injector 7 | V8: likely driver rear bank; coil swap test within that bank |
| P0308 | 8 (V8+) | Coil 8, plug 8, injector 8 | V8: passenger rear bank typically; swap with cyl 6 or 7 |
| P0309-P0312 | 9-12 (V10/V12) | Same template. V10: Viper, Audi R8. V12: S-Class, Aston Martin | Rare. Coil swap test per-cylinder still applies. |
Cylinder Numbering by Engine Family
Inline-4 (Honda, Toyota, Nissan, Hyundai)
1-2-3-4 front to rear from accessory drive end
Ford V8 (5.0 Coyote, 5.4 Triton)
Driver side: 1-2-3-4. Passenger side: 5-6-7-8
GM V8 (5.3L LS/Vortec, 6.2L)
Driver side: 1-3-5-7. Passenger side: 2-4-6-8
Toyota V6 (2GR-FE, 2GR-FKS)
Front bank: 1-2-3. Rear bank: 4-5-6
Honda V6 (J35, J37)
Front bank: 1-2-3. Rear bank: 4-5-6
BMW I6 (N52, N55, B58)
Single bank: 1-2-3-4-5-6 front to rear
Cylinder numbering is not standardised across manufacturers. Always verify in the factory service manual before performing the swap test.
When the Coil Swap Test Is Not Enough
- Coil pack systems (older Ford/GM/VW): You can swap the whole pack to test pack vs plug, but you cannot isolate individual cylinders within the pack.
- P0300 random misfire: Swap test less useful. Check vacuum leak, fuel pressure, all plugs visually before swapping anything.
- Multiple simultaneous codes (P0301 + P0303): Test sequentially. Could be coil + plug combination or a shared wiring fault.
- No-start, no spark across all cylinders: Likely ECU coil-driver transistor failure. Needs oscilloscope and ECU pinout. Not DIY-diagnosable.
Recommended OBD-II Scanners (2026)
BlueDriver
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Innova 3030
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Autel AL319
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ELM327 Bluetooth
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