Code
P0303
LAND ROVER
P — Powertrain
4 ignition failure
Views:
UK: 14
EN: 23
RU: 27
AI status
Completed
Completed
100%
Causes
- Faulty spark plug in cylinder 3 (worn, fouled, incorrect gap)
- Failed ignition coil or coil pack for cylinder 3
- Damaged ignition wiring or connector to cylinder 3
- Fuel injector stuck, clogged, or leaking on cylinder 3
- Low compression or mechanical damage in cylinder 3 (valve, piston, rings)
- Vacuum leak or intake manifold gasket leak affecting cylinder 3
Symptoms
- Check Engine Light (MIL) illuminated, code P0303 stored
- Rough idle or vibration felt from the engine
- Reduced engine power and poor acceleration
- Decreased fuel economy
- Black smoke or strong fuel smell from exhaust (if rich)
- Possible misfire-related noise (popping/backfire) under load
What to check
- Read PCM freeze-frame and live data: misfire counts, misfire cylinder identification, fuel trims, commanded vs actual injector pulse width
- Inspect spark plug condition and gap for cylinder 3; replace if fouled or out of spec
- Swap ignition coil from cylinder 3 with another cylinder and see if code follows
- Visually inspect coil and injector connectors and wiring for damage/corrosion
- Listen for injector operation or use a noid light/scan tool to confirm injector pulses
- Perform a cylinder compression test and/or leak-down test on cylinder 3
Signal parameters
- Cylinder 3 misfire count / misfire ratio
- Ignition coil primary/secondary waveform for cylinder 3
- Fuel injector pulse width and duty cycle for cylinder 3
- Short-term and long-term fuel trim (STFT/LTFT)
- Fuel rail pressure and fuel trim vs load
- Crankshaft position (CKP) and camshaft position (CMP) sensor signals
Diagnostic algorithm
- Retrieve codes and freeze-frame data; note conditions when misfire occurred (rpm, load, temp).
- Clear codes and attempt to reproduce while monitoring live misfire counters and related parameters.
- Inspect and if necessary replace the spark plug for cylinder 3. Re-test.
- Swap the ignition coil from cylinder 3 with a known-good coil on another cylinder. If code follows the coil, replace the coil.
- Swap the fuel injector from cylinder 3 with another cylinder (or test injector operation). If code follows the injector, service or replace the injector.
- Inspect wiring/connectors to the coil and injector for damage, corrosion, or poor connections; repair as needed.
- Perform a compression and/or leak-down test on cylinder 3; compare to other cylinders. If compression is low, investigate head gasket, valves, or piston/rings.
- Check fuel pressure and supply for proper specification and inspect for intermittent low fuel rail pressure.
- Check intake manifold and vacuum for leaks; inspect for exhaust leaks near the affected cylinder.
- If electrical and mechanical checks pass, verify CKP/CMP sensor signals and engine timing. Update PCM software if manufacturer service bulletins apply.
- After repairs, clear codes and perform a road test and convergence check to ensure misfire is resolved.
Likely causes
- Worn or fouled spark plug for cylinder 3
- Failed ignition coil for cylinder 3 (common on coil-on-plug systems)
- Clogged or failing fuel injector on cylinder 3
- Loss of compression in cylinder 3 (worn rings, burnt valve, head gasket)
- Intermittent wiring/connector fault at coil or injector for cylinder 3
- Low fuel pressure or regulator failure causing lean condition
Fault status
Status
P0303 - Cylinder 3 Misfire Detected. Indicates repeated combustion failure on cylinder 3; inspect ignition, fuel, mechanical, and sensor systems for faults.
Repair difficulty: Medium
Diagnostic time: 0.5-3.0 hours
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