P0302: Cylinder 2 Misfire Detected
Title: SAE J2012 generic definition. Manufacturer-specific definitions and enhanced codes can differ; check service information for the exact vehicle.
What P0302 means
The ECM counted repeated misfires on cylinder 2. This page focuses on confirming the misfire with data and catching intermittent ones.
What sets it
Like every single-cylinder misfire code, P0302 sets when the crankshaft-speed misfire counter for cylinder 2 passes a calibrated threshold. Some vehicles set a pending code after one bad trip and a confirmed code after it repeats on a second trip.
Symptoms
- Rough idle or stumble, sometimes only cold or only under load
- Light may come on and go off again for an intermittent misfire
- Flashing check-engine light during a heavy misfire
Is it safe to drive?
General guidance, not a guarantee: As with any misfire, a flashing light means minimize driving and get it repaired quickly. A steady light can usually be driven carefully to a shop. If in doubt, have it towed and diagnosed.
Common causes
Listed roughly from most to least common in general practice. The real order varies by vehicle, mileage and history.
- Spark plug or coil/boot on cylinder 2: still the leading cause on most engines
- Moisture or oil in the plug well: causes misfires on damp mornings or after washing the engine
- Injector on cylinder 2: restricted or intermittently open circuit
- Intake or vacuum leak near cylinder 2
- Valve or compression problem
Test before you replace: diagnostic sequence
General guidance only. Always follow the vehicle manufacturer's service information, specifications and safety procedures. Any figures below are general guidelines that defer to the manufacturer's specification.
- Read freeze frame. Note whether it set cold, at idle or under load. That condition is the one you need to reproduce.
- Look at the Mode $06 misfire data for every cylinder, not just cylinder 2. A low but non-zero count on other cylinders points toward a shared cause such as fuel or a vacuum leak.
- Drive under the freeze-frame conditions while watching live misfire counts, so you can confirm the fault before changing parts.
- Inspect the plug well for oil or water, and inspect the boot for tracking marks.
- Swap the coil, then the plug, to another cylinder and re-test. Move only one part at a time.
- If the misfire does not move, check injector pulse (noid light or scope) and wiring at the injector connector.
- Then test compression and leak-down on cylinder 2.
- After repair, verify with the same drive and confirm the counters stay low.
Bench note: An intermittent misfire you can't reproduce is the classic comeback. Mode $06 counts give you proof before and after the repair.
Related codes
FAQ
What is Mode $06?
It is a standardized OBD II test-results mode (SAE J1979) that shows on-board monitor results, including misfire counts on many vehicles. Many mid-range scan tools can read it.
P0302 comes and goes. Can I ignore it?
A pending code that keeps coming back usually means a real, intermittent fault. Catch it early, before it damages the catalytic converter.
Why only on cold mornings?
Moisture in a cracked boot, or a plug at the end of its life, often misfires cold and clears up warm. A carbon-tracked boot is a common find.
Sources
- SAE J2012, Diagnostic Trouble Code Definitions (standard page; code titles only)
- SAE J1979, E/E Diagnostic Test Modes (Mode $06, readiness, freeze frame)
- California Code of Regulations, 13 CCR 1968.2, OBD II requirements (via Cornell LII)
- US EPA, "What To Do With the Check Engine Light" (EPA420-F-00-041)
Written with AI assistance and reviewed for accuracy; not a substitute for OEM service information. Shop Docs Studio is not affiliated with SAE, EPA, CARB or any vehicle manufacturer.