Worn or fouled spark plug in cylinder 3; Failed ignition coil or coil-on-plug boot for cylinder 3; Faulty fuel injector for cylinder 3 (clogged, leaking, or electrically open); Vacuum leak at the intake manifold runner for cylinder 3; Low compression due to worn piston rings, valves, or head gasket issue on cylinder 3; Wiring damage or loose connector at the cylinder 3 injector or coil; Carbon buildup on intake valves causing poor airflow to cylinder 3

DTC codes / Nissan codes / P1203

P1203 · NissanCylinder 3 Misfire

Q: What does code P1203 mean?

Cylinder 3 Misfire. P1203 on Nissan vehicles indicates that the engine control module has detected a misfire specifically on cylinder 3, typically by monitoring crankshaft speed fluctuations. This means cylinder 3 is not contributing power evenly, which can be caused by ignition, fuel, or mechanical faults.

P1203 on Nissan vehicles indicates that the engine control module has detected a misfire specifically on cylinder 3, typically by monitoring crankshaft speed fluctuations. This means cylinder 3 is not contributing power evenly, which can be caused by ignition, fuel, or mechanical faults.

SystemPowertrain

Code typeNissan specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

Engine runs rough or shakes, especially at idle or during acceleration
Noticeable loss of power and poor throttle response
Check engine light may be steady or flashing if the misfire is severe
Often no symptoms besides the warning light, particularly during light-load cruising
Poor fuel economy or a fuel smell from the exhaust
Shaking or vibration felt through the steering wheel and seat

Common causes, most likely first

Worn or fouled spark plug in cylinder 3
Failed ignition coil or coil-on-plug boot for cylinder 3
Faulty fuel injector for cylinder 3 (clogged, leaking, or electrically open)
Vacuum leak at the intake manifold runner for cylinder 3
Low compression due to worn piston rings, valves, or head gasket issue on cylinder 3
Wiring damage or loose connector at the cylinder 3 injector or coil
Carbon buildup on intake valves causing poor airflow to cylinder 3

How to diagnose and fix it

Scan all stored codes and freeze-frame data to confirm misfire counts and operating conditions
Swap the ignition coil and spark plug from cylinder 3 with a known-good cylinder to see if the misfire moves
Inspect the spark plug condition and gap, and replace if worn or fouled
Perform a cylinder balance test or check misfire counters with a scan tool to isolate the fault
Test the fuel injector for cylinder 3 with a noid light or injector balance test
Check for vacuum leaks at the intake manifold and inspect injector seals
Run a compression test and leak-down test on cylinder 3 to rule out mechanical faults

Don't assume it's just a bad coil

A misfire code for a single cylinder often results from a swapped injector connector or a pinched wire during previous repairs, so always inspect harness routing near cylinder 3.
Nissan engines with direct injection are prone to carbon buildup on intake valves, which can cause a persistent cylinder 3 misfire that ignition parts won't fix.
A flashing check engine light means the misfire is severe enough to damage the catalytic converter, so stop driving and repair immediately.
The code may set intermittently due to a failing coil that only breaks down under high load or heat, so test the coil when the engine is hot.
Low compression from a worn valve seat or piston ring can mimic an ignition misfire, so a compression test is essential before replacing expensive parts.

Can I keep driving with P1203?

If the check engine light is steady and the engine runs smoothly, you can drive cautiously to a repair shop, but avoid hard acceleration and heavy loads. If the light is flashing or the engine shakes violently, stop driving to prevent catalytic converter damage.

Tools that help

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Guidance is general and written for Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.