Cylinder 7 misfire.
P0307 — also written PO3O7, P 0307, 0307 — is the OBD-II code for cylinder 7 misfire detected. Same code, same fix: this page covers every spelling of it.
This is a serious hiccup on a V8 engine where the ECU has clocked that cylinder 7 isn't pulling its weight. Usually hits Range Rovers and big German saloons hard, and if ignored, it'll cook your expensive catalysts.
P0307 is a ignition fault code, typically costing £40–£900 to put right in a UK garage.
What P0307 actually feels like to drive
- The car 'shudders' violently when you try to overtake on the A9, usually between 50-70mph.
- A heavy, rhythmic thumping through the seat at idle, making the car feel like a washing machine on spin cycle.
- The 'Check Engine' light is flashing like a disco—that’s the car telling you your catalytic converter is melting.
- A distinct smell of unburnt petrol from the exhaust pipe, especially when cold.
- Limp home mode: the car feels like it's lost half its horses and won't rev past 3,000rpm.
What causes P0307?
- Spark plug
- Coil
UK vehicles that throw P0307 most often
- Range Rover Sport 5.0 V8 (L320/L494) 2010–2017
- Jaguar XF 5.0 V8 (X250) 2009–2015
- BMW 550i / 650i (N63 engine) 2008–2013
- Audi RS6 4.0 TFSI (C7) 2013–2018
- Mercedes-Benz E500 (W212) 2011–2016
- Land Rover Discovery 4 5.0 V8 2009–2013
How P0307 is fixed
- Plug & coil replacement
The P0307 misdiagnosis that wastes money
I’ve seen dozens of lads spend £300 on a set of Bosch coils and Iridium plugs before they’ve even looked at the wiring harness. On these V8s, the heat under the bonnet is immense, and I often find the loom brittle or a connector not clicked home properly. The real 'gotcha' on the AJ-V8 or the BMW N63 is a leaky rocker cover gasket; oil seeps into the spark plug well for cylinder 7, drowns the coil, and kills it. Changing the coil without fixing the leak is just throwing money down the drain—it'll blow again in a fortnight.
What a UK garage should charge for P0307
A basic diagnostic plug-in usually runs you £50 to £80 at a good indie. For a single Bosch coil and a decent NGK plug, you’re looking at £80 to £140 fitted. However, if it's a direct-injection V8 and the injector has failed, you're easily into £450–£600 for a single cylinder. If you go to a main dealer, expect that to double. If you've been driving it while flashing and nuked the cat, you can add another £800+ to that bill for a quality aftermarket unit.
P0307 repair cost in the UK
Most P0307 repairs land between £40–£900 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 P0307
Don't let a garage just swap parts until the light goes out. Insist they do a 'coil swap' test: move the coil from cylinder 7 to cylinder 5 and see if the code changes to P0305. If it does, it's the coil. If the misfire stays on 7, you've got an injector or compression issue. If they haven't got a decent scan tool like a Snap-on Triton or an Autel to check the live misfire counters, find another workshop. Also, ask for a compression test before you agree to any major engine work—it takes 20 minutes and saves you from buying a new coil for a dead engine.
Can you drive with P0307?
Drive gently.
Urgency: high.