P1303
Cylinder 3 Misfire.
- Honda
- Powertrain
- Manufacturer code
- High severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 3
- AreaIgnition system or misfire
- 03
- FaultThe specific fault in that area
What it means
On Honda, P1303 means the engine control unit has detected misfires on cylinder 3. It sets this when crankshaft speed signals show cylinder 3 is not contributing combustion as expected. The exact detection thresholds and whether it is cylinder-specific on a given engine can vary by model and year.
Symptoms
- Engine running rough or shaking at idle
- Flashing or steady malfunction warning light
- Hesitation or loss of power under acceleration
- Smell of unburnt fuel from the exhaust
- Poor fuel economy
- Difficult starting or occasional stalling
Possible causes
- Worn, fouled or incorrectly gapped spark plug on cylinder 3likely
- Faulty ignition coil or coil connector on cylinder 3likely
- Blocked, leaking or failed fuel injector on cylinder 3, or its wiringpossible
- Vacuum or intake leak affecting the cylinder 3 intake runner or gasketpossible
- Low compression on cylinder 3 (valve, valve clearance, piston ring or head gasket problem)possible
- Poor fuel quality or contaminationrare
- Crankshaft position sensor or reluctor signal fault causing false misfire detectionrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data (engine load, speed, temperature) to see when the misfire occurs
- Check for other misfire codes on neighbouring cylinders, as this points towards a common cause such as fuel or a vacuum leak
- Inspect the cylinder 3 coil connector, wiring and injector connector for damage, corrosion or looseness
- Remove the cylinder 3 spark plug and check its condition, type and gap against the specification for your engine
- Swap the cylinder 3 coil with another cylinder, clear the codes and see whether the misfire follows the coil
- Test the cylinder 3 injector for correct resistance and operation, and check for a proper injector pulse
- Inspect the intake manifold and gaskets for leaks, for example with a smoke test
- Carry out a compression or leak-down test on cylinder 3, and check valve clearances where the engine design requires it
How to fix
- Replace the spark plugs with the correct type and gap, ideally as a full set
- Replace the faulty ignition coil, and repair or replace damaged connectors
- Clean or replace the faulty cylinder 3 injector, or repair its wiring
- Repair intake leaks by replacing the faulty gasket, hose or seal
- Carry out the necessary mechanical engine repair if compression is low, such as valve adjustment or valve or head gasket work
- Replace the crankshaft sensor or repair its wiring if the signal is proven faulty
Can I keep driving?
High severity
Avoid driving if the warning light is flashing, as unburnt fuel can overheat and damage the catalytic converter. If the light is steady and the car runs reasonably, drive gently for a short distance only to get it repaired.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.