TORKO

P0303 Cylinder 3 misfire detected

What P0303 means

The engine computer watches crankshaft speed and has seen that cylinder 3 is not firing properly: the fuel in that cylinder is not burning, or burning only partly. Unburned fuel goes into the exhaust, where it can overheat and destroy the catalytic converter.

P0303 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.

At a glance

Severity
High
Typical repair cost
40–400 €
Workshop time
0.3–4 h
Repair difficulty
Easy
DIY possible
Yes
Check engine light
Yes
Affects emissions test
Yes

Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.

Symptoms

Common causes

  1. Worn or fouled spark plug in cylinder 3
  2. Failing ignition coil (or plug lead) on cylinder 3
  3. Clogged, leaking or electrically faulty cylinder 3 fuel injector
  4. Vacuum leak near that cylinder, such as an intake manifold gasket
  5. Low compression from a valve, piston ring or head gasket problem

Can I keep driving with P0303?

Get it checked today or tomorrow and drive gently until then. If the check engine light is flashing, stop driving: the misfire is severe enough to damage the catalytic converter quickly.

What to check first

  1. Read the freeze-frame data and the misfire counters to see when cylinder 3 misfires (cold, idle, under load).
  2. Swap the cylinder 3 ignition coil with a neighbouring cylinder, clear the codes and drive: if the misfire moves, replace the coil.
  3. Remove and inspect the cylinder 3 spark plug for wear, oil or fuel fouling, cracks or a wide gap.
  4. If ignition is fine, check the cylinder 3 injector, then do a compression or leak-down test.

Related codes

Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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