- Vehicles
- Cars
P0304
P0304 (generic OBD-II): cylinder 4 misfire detected
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
The engine computer detected failed combustion in cylinder 4. Check whether the engine light flashes: if it does, stop somewhere safe. Then read the codes and save the freeze frame without clearing it.
Safety first
Stop and check this first
- With a flashing engine light, the misfire can damage the catalytic converter; stop and do not keep driving to see whether it goes off.
Safe checks you can perform
- Engine light steady or flashing
- All codes and the freeze frame data
- Service bulletins and campaigns for your VIN
Leave these tasks to a qualified professional
- Do not attempt this professional task: Swap test on cylinder 4
- Do not attempt this professional task: Verification under the same conditions
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Swap test on cylinder 4
What they doThe technician swaps the cylinder 4 coil with another cylinder's coil, recreates the freeze frame conditions and reads the fault memory again.
They must show youboth fault memory printouts, before and after the swap, and which cylinder the misfire moved to.
In writingwhich part is replaced, why the test points to it, and the final check under the same conditions in which the code set.
Verification under the same conditions
What they doAfter the repair, the technician drives or runs the engine under the conditions recorded in the freeze frame and confirms the cylinder misfire counter does not rise.
They must show youthe cylinder 4 misfire data after the repair.
In writingthe conditions of the final test and that the monitors have completed again.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Engine light steady or flashing
- Who:
- you, watching the instrument cluster with the engine running.
- How:
- check whether the engine light stays on or flashes while you drive. Do not confuse this with a brief flash at key-on with the engine off: some cars do that only to show that the OBD monitors have not finished.
- Result that matters:
- whether the light flashes with the engine running.
- If it flashes while driving:
- there is a misfire that can damage the catalytic converter. Stop somewhere safe and follow your owner's manual; Honda, for example, says to stop away from flammable objects, switch the engine off for at least 10 minutes and take the car to a dealer.
- If it stays on:
- note P0304 and book an inspection. A steady light does not rule the misfire out, because the regulation lets some cars cut fuel instead of flashing the light.
- Evidence to keep:
- whether it flashed or stayed on, in what situation (cold, idle, uphill, accelerating) and since what date.
With a flashing light, do not keep driving to see whether it goes off by itself.
Evidence: Nissan USA malfunction indicator light guide · Volkswagen USA warning and indicator lights · Title 13, California Code Regulations, Section 1968.2, Malfunction and Diagnostic System Requirements (OBD II) · Honda 2020 HR-V Owner's Guide - Dashboard details (malfunction indicator lamp)
All codes and the freeze frame data
- Who:
- you, with a generic OBD-II reader in the diagnostic socket.
- How:
- read the confirmed and pending codes and save the freeze frame data for P0304 before anyone clears anything.
- Result that matters:
- whether other codes appear alongside the misfire and under what conditions it was stored.
- If there are codes from other systems (sensors, injectors, mixture, low fuel level):
- the workshop should resolve them before the misfire, as Volkswagen's diagnostic aid requires.
- If only misfire codes appear:
- the freeze frame (engine speed, load, temperature) tells the workshop under which conditions to reproduce the fault.
- Evidence to keep:
- a photo or screenshot of the full code list and of the freeze frame screen.
Plug in and read the tool with the car parked somewhere safe, never while driving. Do not clear the codes: clearing them also erases the freeze frame data the workshop needs.
Evidence: Volkswagen TSB 2025089 engine misfire diagnostic aid · Title 13, California Code Regulations, Section 1968.2, Malfunction and Diagnostic System Requirements (OBD II)
Service bulletins and campaigns for your VIN
- Who:
- you, asking your brand's authorised service.
- How:
- give your vehicle identification number (VIN) and code P0304, and ask whether there is a campaign or service bulletin about misfires for your model and engine.
- Result that matters:
- whether a bulletin matches your model, year and engine.
- If it matches:
- the workshop should apply that procedure first (Toyota, for example, published an engine computer reprogramming for one model with these codes) before replacing parts.
- If there is no bulletin for your car:
- a full ignition, injection, connection and fuel diagnosis is needed.
- Evidence to keep:
- the bulletin or campaign number, or the answer that there is none, with the date.
Evidence: Volkswagen TSB 2025089 engine misfire diagnostic aid · Toyota T-SB-0148-19 Highlander HV P0301-P0306
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Vehicles
- Brand
- OBD-II genérico
- Product type
- Cars
Known code variants
- P0304
- P0304 cylinder 4 misfire
- P0304 fallo de encendido cilindro 4
- P0304 OBD2
What it means
P0304 is the generic code for a misfire detected in cylinder 4. The misfire monitor uses the crankshaft and camshaft sensor signals to work out whether that cylinder contributes less rotation than expected. The code locates the cylinder, not the part: the coil or spark plug can fail, but so can the injector, a connection or ground, or the fuel. Volkswagen notes that many replaced coils were not the cause.
Warnings and stop conditions
- Highsource verified
With a flashing engine light, the misfire can damage the catalytic converter; stop and do not keep driving to see whether it goes off.
Evidence: Title 13, California Code Regulations, Section 1968.2, Malfunction and Diagnostic System Requirements (OBD II) · Honda 2020 HR-V Owner's Guide - Dashboard details (malfunction indicator lamp)
Symptoms and causes
Probable causes · in order
- Cylinder ignitionPossible
Coil, spark plug or their connection. It shows up when the misfire moves to another cylinder after swapping the cylinder 4 coil.
Evidence: Volkswagen TSB 2025089 engine misfire diagnostic aid · Toyota T-SB-0148-19 Highlander HV P0301-P0306
- Connections, grounds or installationPossible
Volkswagen lists incorrect coil installation, loose or damaged connections and grounds. Suspect it if the misfire is intermittent or appeared after a recent repair.
Evidence: Volkswagen TSB 2025089 engine misfire diagnostic aid
- Fuel or depositsPossible
Poor fuel quality and deposits on injectors and intake valves can cause sporadic misfires, especially when cold.
Evidence: Volkswagen TSB 2033846 sporadic misfire faults · Volkswagen TSB 2025089 engine misfire diagnostic aid
- Engine computer softwareLess common
For some models the manufacturer publishes a reprogramming for these codes. It only applies if the bulletin matches your model and engine.
Evidence: Toyota T-SB-0148-19 Highlander HV P0301-P0306
Virtual technician
Does P0304 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Nissan USA malfunction indicator light guide
Nissan USA · official_doc
- 2
Volkswagen TSB 2033846 sporadic misfire faults
Volkswagen Group of America · 2016 · service_bulletin
- 3
Volkswagen TSB 2025089 engine misfire diagnostic aid
Volkswagen Group of America · 2013 · service_bulletin
- 4
Volkswagen USA warning and indicator lights
Volkswagen USA · official_doc
- 5
Toyota T-SB-0148-19 Highlander HV P0301-P0306
Toyota Motor Sales USA · 2019 · service_bulletin
- 6
Ford 2020-2023 gasoline OBD system operation
Ford Motor Company · 2023 · manual
- 7
California Air Resources Board · 2006 · official_doc
- 8
Honda 2020 HR-V Owner's Guide - Dashboard details (malfunction indicator lamp)
American Honda Motor Co. · 2020 · manual
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