P0300 Random/Multiple Cylinder Misfire Detected

What does fault code P0300 mean?

P0300 means your engine has a random or multiple cylinder misfire. Get AI diagnosis, UK repair costs and fixes for fault code P0300. When this fault is detected, the ECU (Engine Control Unit) stores the code and illuminates the check engine light (also called the engine management light or malfunction indicator lamp) on your dashboard.

All cars sold in the UK since 1996 use the standardised OBD-II diagnostic system, meaning fault code P0300 can affect any manufacturer — including Ford, Vauxhall, BMW, Volkswagen, Toyota, Mercedes-Benz, Audi, Renault, Peugeot, Nissan, Honda, Hyundai, Kia, and all others. The code is read using an OBD-II scanner plugged into the 16-pin diagnostic port, usually located under the dashboard on the driver's side.

Symptoms of fault code P0300

These are the most common symptoms UK drivers report when this code is active:

• Check engine light on, often flashing (serious)
• Rough or shaky engine at idle
• Loss of power during acceleration
• Engine stumbling or hesitating
• Increased fuel consumption
• Strong fuel smell from exhaust

Note that some vehicles show no drivability symptoms at all — the check engine light may be the only sign. This is why scanning the fault code is essential rather than guessing at the cause.

What causes P0300?

Listed from most to least common based on UK garage data:

1. Worn or fouled spark plugs (most common cause)
2. Faulty ignition coils or HT leads
3. Fuel injector not firing correctly
4. Low compression in one or more cylinders
5. Incorrect ignition timing
6. Vacuum leak causing a lean misfire

It is important to diagnose the root cause before replacing parts. Many unnecessary and expensive repairs happen because the most expensive component is replaced first without proper testing. Always work through the diagnostic steps systematically.

How to fix P0300 — step by step

Work through these steps in order to avoid unnecessary parts replacement:

1. Start with spark plugs — inspect and replace as a set if over 30,000 miles
2. Test each ignition coil by swapping with a known good coil — if the misfire moves, replace the coil
3. Check fuel injectors with live data — a dead injector will show as a lean cylinder
4. Perform a compression test if plugs and coils check out fine

After any repair, clear the fault code with an OBD-II scanner and carry out a test drive. If the code returns, continue to the next diagnostic step. For a personalised repair guide specific to your vehicle's make, model, year and engine, use our AI Diagnostic Report below.

UK vehicles commonly affected by P0300

These models are frequently seen with this fault code in UK garages:

• Ford Fiesta/Focus (petrol)
• Vauxhall Corsa/Astra (petrol)
• BMW 1/3 Series
• Renault Clio/Megane
• Peugeot 207/208
• Volkswagen Polo/Golf

This code can appear on any OBD-II vehicle (all UK cars since 1996) but is more common on the models listed above. If your vehicle is not listed, it does not mean the code cannot affect it — it simply means these models are statistically more frequent in UK repair data.

DIY difficulty and cost guide

Difficulty: Easy to medium — spark plug and coil replacement is beginner-friendly. Fuel injector or compression issues need a professional.

UK repair cost estimate: £80–£500 including parts and labour at average UK workshop rates (inc. VAT). Independent garages are typically 30–50% cheaper than main dealers. Always get at least two quotes.

Prevention: Replace spark plugs every 30,000–40,000 miles, use quality fuel, and service the ignition system on schedule.

P0300 and the UK MOT test

Fault code P0300 is likely to cause an MOT failure. Under current DVSA testing standards, an illuminated malfunction indicator lamp (MIL / check engine light) is an automatic MOT failure, regardless of whether the vehicle is otherwise roadworthy. This means you must resolve this fault before your MOT test.

Even if the light is not currently on, if the fault is intermittent it could reappear during the test. Use our AI Diagnostic Report to understand the MOT risk specific to your vehicle and get advice on whether it is safe to proceed to your test.

P0300 guides by vehicle make

Select your vehicle for a specific diagnosis guide with UK repair costs:

Frequently asked questions about P0300

Related OBD2 fault codes

These fault codes are commonly found alongside P0300 or share similar causes: