Cylinder 3 misfire on Vauxhall — A14NET coil pack and Z19DTH injector loom chafe.
Vauxhall P0303 — Cylinder 3 misfire on Vauxhall — A14NET coil pack and Z19DTH injector loom chafe. Typical UK independent garage cost: £70–£500.
What actually causes P0303 on a Vauxhall
Z19DTH P0303 with intermittent rough running is usually injector loom chafe on the rocker cover stud — easy to miss visually, drops out on heat-soak. On A14NET it's a coil pack 90% of the time.
Vauxhall engines that log P0303
- 1.4 Turbo A14NET (Astra J/Corsa E)
- 1.6 CDTi B16DTH (Astra J/Insignia)
- 1.9 CDTi Z19DTH (Vectra/Zafira)
How we diagnose P0303 on a Vauxhall
- Visual inspection of injector loom along rocker cover
- Wiggle test injector connectors with engine running
- Read injector correction values
- Compression test if cold-misfire only
The common misdiagnosis to avoid
Aftermarket injectors on Z19DTH cause new fault codes within 1,000 miles — only OEM Bosch reman with new copper washers.
Vauxhall P0303 repair cost in the UK
Expect £70–£500 including parts and labour at an independent garage. Main-dealer quotes on Vauxhall are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Bob's workshop tip
Z19DTH P0303 — check the loom before the injector. A £15 repair pin saves a £350 injector job.
Codes usually seen alongside P0303 on Vauxhall
- P0301
- P0302
- P0304
- P0300
Symptoms drivers report with P0303
- The engine 'kangaroos' or hesitates when you’re pulling away from a roundabout.
- The car feels like it’s 'chugging' or running on three cylinders when idling at traffic lights.
- The EML (Engine Management Light) starts flashing when you’re pushing it up a steep hill or overtaking.
- A heavy smell of unburnt petrol coming from the exhaust pipe at cold start.
- The car struggles to 'pick up' from 2,000 RPM in 4th or 5th gear.
Repairs that clear P0303
- Plug & coil replacement
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0303 guide.