Faulty ignition coil or spark plug in cylinder 3; Worn or fouled spark plug; Clogged or failing fuel injector for cylinder 3; Vacuum leak affecting cylinder 3 intake runner; Low compression due to worn piston rings, valves, or head gasket; Faulty PCM or wiring issue in the ignition coil circuit

DTC codes / Honda codes / P1203

P1203 · HondaCylinder 3 Misfire

Q: What does code P1203 mean?

Cylinder 3 Misfire. P1203 is a Honda-specific trouble code indicating that the powertrain control module (PCM) has detected a misfire on cylinder number 3, typically by monitoring crankshaft speed fluctuations. The PCM sets this code when the misfire count exceeds a threshold that could damage the catalytic converter or affect emissions.

P1203 is a Honda-specific trouble code indicating that the powertrain control module (PCM) has detected a misfire on cylinder number 3, typically by monitoring crankshaft speed fluctuations. The PCM sets this code when the misfire count exceeds a threshold that could damage the catalytic converter or affect emissions.

SystemPowertrain

Code typeHonda specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

Check Engine Light (CEL) illuminated, often flashing if the misfire is severe
Noticeable engine vibration or shaking, especially at idle or during acceleration
Reduced engine power and poor acceleration
Rough idle or stalling
Often no symptoms besides the warning light, especially if the misfire is intermittent
Poor fuel economy

Common causes, most likely first

Faulty ignition coil or spark plug in cylinder 3
Worn or fouled spark plug
Clogged or failing fuel injector for cylinder 3
Vacuum leak affecting cylinder 3 intake runner
Low compression due to worn piston rings, valves, or head gasket
Faulty PCM or wiring issue in the ignition coil circuit

How to diagnose and fix it

Scan all codes and check freeze frame data to confirm the misfire conditions
Inspect spark plug and ignition coil for cylinder 3; swap with a known-good cylinder to see if the misfire moves
Perform a compression test and leak-down test to rule out mechanical issues
Check fuel injector operation and perform a balance test or swap injectors
Inspect intake manifold for vacuum leaks and check PCV system
Verify ignition coil circuit wiring and connectors for damage or corrosion
If all else fails, perform a crankshaft position variation relearn or check PCM software updates

Honda Cylinder 3 Misfire: Beyond the Usual Suspects

Honda engines are known for EGR port clogs that can cause misfires, particularly on V6 models; a clogged EGR passage can disproportionately affect cylinder 3.
A misfire code does not always mean the ignition coil is at fault; valve clearance issues on Honda engines can cause misfires that only appear when the engine is cold.
The PCM may set P1203 even if the misfire is intermittent and not felt by the driver; always check for stored history codes and freeze frame data.
Fuel quality plays a role; low-octane or contaminated fuel can cause misfires that set this code, so verify fuel pressure and quality before replacing parts.
Honda's misfire detection can be sensitive to crankshaft position sensor signal interference; check for aftermarket accessories or poor grounds that may introduce noise.

Can I keep driving with P1203?

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

Tools that help

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