The engine is misfiring across multiple cylinders. This is a serious code that can damage the catalytic converter quickly.
P0300 — also written PO3OO, P 0300, 0300 — is the OBD-II code for random / multiple cylinder misfire detected. Same code, same fix: this page covers every spelling of it.
This is the 'bucking bronco' code where the engine can't decide which cylinder to fire properly. It's a common headache on Astra J 1.4 turbos and older VAG 1.2 TSI engines where the timing chain has started to stretch.
P0300 is a ignition fault code, typically costing £60–£1200 to put right in a UK garage.
What P0300 actually feels like to drive
- The car feels like it's 'kangaroos' down the High Street when you're in a high gear at low revs.
- The engine management light isn't just on; it's flashing at you like a disco light—that means 'stop now or kill the cat'.
- It idles like a bag of spanners when you're sat at the traffic lights, making the whole dashboard shake.
- A heavy smell of unburnt petrol from the exhaust, especially on cold starts.
- Huge flat spot when you try to overtake on the A9; the power just goes missing.
What causes P0300?
- Worn spark plugs or coil packs
- Faulty fuel injectors
- Low fuel pressure
- Vacuum leak
- Bad timing belt/chain
- Compression problem
UK vehicles that throw P0300 most often
- Vauxhall Corsa/Astra 1.2 & 1.4 (A14XER/NET) 2010-2015
- Volkswagen Golf/Polo 1.2 TSI (CBZA/CBZB) 2009-2014
- Ford Fiesta 1.0 EcoBoost (the 'Fox' engine) 2012-2017
- BMW 1 Series/3 Series (N43/N53 engines) 2007-2012
- Nissan Qashqai 1.2 DIG-T (HRA2) 2013-2018
- Mini Cooper 1.6 (N12/N14 engines) 2006-2013
How P0300 is fixed
- Replace spark plugs and ignition coils
- Test fuel injectors
- Check timing
- Compression test if persistent
The P0300 misdiagnosis that wastes money
I see it all the time: folk see 'misfire' and immediately throw a cheap set of Euro Car Parts special coil packs and spark plugs at it. If it’s a Vauxhall or a Ford, they might get lucky for a week, but P0300 is often a 'ghost' code. Half the time, the real culprit is a cheeky vacuum leak on a perished breather pipe or a gummed-up EGR valve sticking open. I’ve seen people spend £400 on ignition components only to find a £15 split rubber hose was leaning out the mixture and causing the stumble.
What a UK garage should charge for P0300
A basic diagnostic plug-in is £50-£80. If it's just a set of Bosch plugs and a decent Delphi coil pack, you're looking at £180–£250 fitted at an Indy. However, if we're talking a stretched timing chain on a TSI or a cracked piston on a 1.2 Vauxhall, you're easily north of £1,200. A main dealer will likely double those prices and try to sell you a seasonal health check you don't need. Factor in £150 for a new catalytic converter if you've been driving with the light flashing for a week.
P0300 repair cost in the UK
Most P0300 repairs land between £60–£1200 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0300
Don't let a garage just 'read the codes' and charge you £60 for the privilege. Insist on a 'live data' check. On my Snap-On tool, I can watch the misfire counters for each cylinder in real-time. If cylinder 2 is jumping but the others are quiet, it's not 'random' and we can swap coils to see if the fault follows. Also, ask them to check the 'long-term fuel trims'. if they are sky-high (above 10%), you've got an air leak, not a spark problem. If they want to replace the ECU straight away, get your keys and run—it's rarely the brain.
Can you drive with P0300?
Avoid driving. Continued misfires will destroy your catalytic converter (£500–£1,500 repair).
Urgency: high.