Misfire on cylinder 9 (V10/V12 engines only).
P0309 — also written PO3O9, P 0309, 0309 — is the OBD-II code for cylinder 9 misfire. Same code, same fix: this page covers every spelling of it.
This code means cylinder number 9 has stopped pulling its weight. You'll only ever see this on high-performance V10 or V12 beasts like an Audi R8, BMW M5, or a big Jag.
P0309 is a ignition fault code, typically costing £60–£800 to put right in a UK garage.
What P0309 actually feels like to drive
- The engine sounds like a bag of spanners at idle, vibrating through the seat.
- Massive hesitation when you try to overtake on the A9.
- A distinct 'chugging' noise from the exhaust pipe.
- The EML (check engine light) is flashing at you, not just staying solid.
- A heavy smell of unburnt petrol from the tailpipes.
- The car has gone into 'Limp Mode', capping your revs and power.
What causes P0309?
- Coil pack
- Spark plug
- Injector
- Compression loss
UK vehicles that throw P0309 most often
- Audi R8 5.2 FSI V10 (2009-2015)
- BMW M5/M6 E60/E63 (S85 V10 engine) 2005-2010
- Audi S6/S8 5.2 FSI (2006-2011)
- Jaguar XJ/XK 5.0 V8 (Wait, usually V12/V10 only, so think Aston Martin DB9/DBS V12)
- Volkswagen Touareg 5.0 V10 TDI (2003-2010)
- Lamborghini Gallardo (common V10 platform sharing with Audi)
How P0309 is fixed
- Swap coil to prove
- Replace plugs
- Compression test
The P0309 misdiagnosis that wastes money
I've seen so many lads just fire a new coil pack at these V10s and V12s because it’s the 'obvious' fix. On a high-mileage Audi R8 or an older S6, P0309 is often not the coil at all—it’s the carbon build-up on the intake valves or a lazy injector. People spend £150 on a Bosch coil and £20 on a plug, only for the light to come back on two days later. The real culprit is usually the direct injection soot choking the port, preventing a clean burn.
What a UK garage should charge for P0309
Diagnosis usually starts at £60-£90 for a scan and basic health check. If it’s just a Bosch coil pack, you're looking at £120-£180 including labour. However, if the injector is shot on a BMW M5, you're easily talking £450-£600 because of the strip-down time. If we find low compression on a V10, you’re looking at a four-figure bill (£800 minimum just to get the head off) and a very bad day. Main dealers will easily double these prices for the 'prestige' badge.
P0309 repair cost in the UK
Most P0309 repairs land between £60–£800 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 P0309
If you're bringing a V10 or V12 to me with P0309, don't let a garage just 'try' parts. Insist they do a 'coil swap' first—move the coil from cylinder 9 to cylinder 1. If the code stays on 9, you know the coil is fine. Also, ask for a fuel trim readout. If it's lean, it's an injector or air leak; if it's rich, it's ignition. On these big engines, access to cylinder 9 is usually a nightmare, so if you're pulling the manifold, change all the plugs at once. It's false economy otherwise.
Can you drive with P0309?
Reduce load, book in.
Urgency: high.