What does it mean?
P1394 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 4 Misfire Detected Catalyst Damaging, Fuel Level Low .
Symptoms
- MIL flashing during the misfire, then staying on
- Severe vibration at idle, engine feels like it is running on three cylinders
- Marked loss of power, hesitation and surging under acceleration
- Low fuel warning present at the same time as the fault
- Strong fuel smell and possible exhaust popping
- Stalling risk when cornering or braking hard with a low tank
Likely causes
- Fuel starvation because the tank level is too low for the pump pick-up
- Spark plug on cylinder 4 worn out, oil fouled or damaged
- Ignition coil breaking down under load on that cylinder
- Injector on cylinder 4 blocked, leaking or with an open winding
- Localised vacuum leak at the intake port or injector seal
- Compression loss on cylinder 4: valve sealing problem, worn rings, cam or lifter wear
- Failing fuel pump or restricted filter reducing rail pressure under load
How to fix it
- Fill the tank and clear the code, then see whether the misfire returns
- Verify with live data which cylinder is actually accumulating misfire counts
- Exchange the coil and plug from cylinder 4 with a neighbouring one to isolate the failing part
- Read the removed plug: its colour and deposits point to fuel, oil or ignition problems
- Check injector resistance, spray behaviour and fuel trim response
- Measure fuel pressure while driving under load and inspect the filter and strainer
- Carry out a compression and leak down test on cylinder 4 if the fault persists
- Keep engine load low until repaired to avoid destroying the catalytic converter