What P0305 means
The engine computer has found that cylinder 5 isn't firing properly, so the engine shakes or stumbles, especially at idle or when pulling hard. This code only appears on engines with five or more cylinders. The ignition coil or spark plug for cylinder 5 is the usual cause.
How the engine computer detects it
The engine module detects misfire from crankshaft speed: a cylinder that does not fire gives no acceleration impulse. At a catalyst-damaging rate (CARB: at least 5 % per 200 revolutions) the warning light flashes; at an emissions-relevant rate (at least 1 % per 1,000 revolutions – GM about 2–5 %, Ford 0.9–1.5 %) it comes on after two trips. Ford and GM may shut off a misfiring cylinder's injector to protect the catalyst. P0305 means more than 90 % of the detected misfires fall on cylinder 5. Usual causes are the ignition coil or spark plug of that cylinder, its injector, or low compression; a quick test is to swap coil or plug with a neighbouring cylinder and see whether the misfire moves. GM found heat-damaged coils on its 3.6 V6 caused by a stuck ignition signal – the damaged coil need not be on the misfiring cylinder.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on, flashing at a catalyst-damaging rate
- Rough idle, jerking, vibration
- Loss of power, hesitation
- Smell of unburnt fuel, higher consumption
Common causes
- Ignition coil of cylinder 5 faulty (coil, connector, ground) Most likely
- Spark plug of cylinder 5 worn, sooted, cracked or wrongly gapped Most likely
- Injector of cylinder 5 clogged or leaking, or its control Possible
- Low compression on cylinder 5 (valve, rings, head gasket) or local false air Less likely
- Water or oil in the plug well Less likely
How to diagnose P0305
- Find cylinder 5 on your engine. Makers number cylinders differently, so on a V6 or V8 it can be on either side. A cylinder numbering diagram in the repair manual shows where it is.
- Check for other codes. If cylinders next to 5 on the same side also misfire, or lean codes are set, look for an intake leak or fuel problem on that side first.
- Move the cylinder 5 coil to another cylinder on the same side, clear the code and drive. If the misfire moves to that cylinder, replace the coil.
- Remove the cylinder 5 spark plug and check it for cracks, oil, heavy deposits or a worn electrode. On some V6 engines the rear plugs sit under the intake manifold, which makes this a bigger job.
- If coil and plug check out, have the cylinder 5 injector tested or swapped with a neighbor.
- A compression or leak-down test on cylinder 5 shows whether a valve, rings or the head gasket is the problem.
Vehicles that report P0305 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Chrysler Pacifica | 2005–2019 | 16 | — | |
| Ford F-150 | 2011–2022 | 8 | 21k | |
| Jeep Wrangler | 2012–2018 | 6 | — | |
| Honda Pilot | 2014–2019 | 5 | — | |
| Chevrolet Silverado 1500 | 2010–2020 | 4 | — | |
| Dodge Ram 1500 | 2011–2012 | 4 | 138k |
Counts of owner complaints to the NHTSA that mention P0305 (92 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 3
- Ignition system or misfire
- 05
- Specific fault
Questions drivers ask
Can I drive with code P0305?
A flashing check engine light means stop driving as soon as it's safe: unburned fuel is overheating the catalytic converter. If the light is steady and the engine runs fairly smoothly, a short, gentle trip to a shop is usually OK.
Will my car pass an emissions inspection with P0305?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0305. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.