P0305: Cylinder 5 is misfiring
Cylinder 5 Misfire Detected
If the light is flashing, stop now. Converter damage happens in minutes with a raw misfire. A steady light means get to a shop that day. Do not push a V6 or V8 that is misfiring.
What it means
P0305 means the PCM's misfire monitor detected that cylinder 5 is not firing consistently. Cylinder 5 only appears on V6, V8, or inline-6 engines. On V8 engines, cylinder 5 is often toward the rear of one bank, making its coil and injector connectors harder to reach and inspect. The physical location matters because rear cylinders on V8s often suffer more from heat soak and suffer wiring harness damage from exhaust shield contact. The combustion failure risk is the same as any misfire: catalytic converter damage from unburned fuel.
Common causes
- Failed ignition coil on cylinder 5Coil failure is the most common single-cylinder misfire cause. Swap it first.
- Worn spark plug on cylinder 5On V8s where cylinder 5 is at the back of a bank, plug replacement is often deferred and the plug ends up very worn.
- Clogged or failed fuel injector on cylinder 5Injector failure often accompanies P0205 in the code list.
- Compression loss on cylinder 5More common on higher-mileage engines. A compression test will confirm.
What it costs
- Spark plug set$100 to $300 (access labor may be higher on V8s)
- Ignition coil (one)$150 to $450 installed
- Fuel injector (one)$150 to $450 installed
- Compression or valve repair$1,000 to $3,500
Symptoms
- Check engine light flashing or steady
- Noticeable vibration, especially at idle and low speeds
- Power loss when accelerating
- Fuel economy drop
- Possible smell of raw fuel from the exhaust
What to do next
On a V8 or V6, access to cylinder 5 may require removing a coil cover or exhaust heat shield. Swap the coil with a nearby cylinder and road test to see if the misfire moves. If the coil is fine, check the plug. On rear bank cylinders, plugs often get forgotten during routine maintenance and can be the sole cause.
Lewis shows the misfire event rate on cylinder 5 versus adjacent cylinders so you can see whether it is an isolated failure or spreading. Download Lewis.
Related codes
FAQ
- Only V8 or V6 engines have cylinder 5, right?
- Cylinder 5 exists on V6, V8, V10, V12, and inline-5 or inline-6 engines. It does not exist on four-cylinder engines.
- Why is cylinder 5 harder to access than cylinder 1?
- On most V8s, cylinder 5 is at the rear of one bank, near the firewall. Spark plug and coil removal often requires ratchet extensions and sometimes removing intake components.
- My truck idles fine with P0305. Can I wait?
- Do not wait. A smooth idle does not mean no misfire. The PCM may be compensating. A flashing light is the urgent signal, but even a steady-light misfire will damage the converter over time.