Code
P1204
INFINITI
P — Powertrain
Cylinder 4 Misfire
AI status
Completed
Completed
100%
Causes
- Faulty ignition coil or ignition coil primary/secondary circuit fault for cylinder 4
- Bad or fouled spark plug in cylinder 4
- Fuel injector fault (stuck, clogged, or electrical failure) for cylinder 4
- Low compression or mechanical damage (valve, piston, ring) in cylinder 4
- Wiring/connectors or poor ground to injector or coil for cylinder 4
- Intake manifold gasket leak or vacuum leak affecting cylinder 4
Symptoms
- Check Engine Light (MIL) illuminated
- Rough idle or vibration localized to cylinder 4
- Reduced engine power and hesitation under load
- Poor fuel economy
- Possible misfire codes or misfire counts in freeze frame data
- Fuel smell, backfiring, or increased exhaust emissions
What to check
- Connect a diagnostic scan tool: read P1204 and any other stored codes, view freeze frame and misfire counters per cylinder
- Check live data: cylinder-specific misfire counts, short-term and long-term fuel trims, O2 sensor response, and fuel rail pressure
- Visually inspect spark plug, ignition coil, wiring and connectors at cylinder 4 for damage, corrosion, or poor connection
- Swap coil from cylinder 4 with another cylinder and re-check misfire to see if fault moves (if coils are single-cylinder coils)
- Swap injector from cylinder 4 with another cylinder and re-check misfire to see if fault moves (where practical and safe)
- Perform a compression test and/or leak-down test on cylinder 4 and compare to other cylinders and factory specs
Signal parameters
- Misfire count for cylinder 4 (counts/min or counts per drive cycle) — present in live data
- Injector pulse width for cylinder 4 (ms) — compare to other cylinders; typical idle pulse width ~2–5 ms (refer to factory spec)
- Short-term and long-term fuel trim (%) — significant imbalance may indicate fueling issue
- Fuel rail pressure (kPa or PSI) — check vs factory spec
- Ignition coil primary voltage and secondary waveform — look for weak or missing spark signatures
- Spark plug resistance and electrode condition; plug gap (mm/in) per spec
Diagnostic algorithm
- Retrieve and record all DTCs and freeze frame data with a scan tool; note misfire counts and conditions when code set
- Visually inspect spark plug, coil, injector, harness and connector for cylinder 4; repair any obvious damage or poor connections
- Clear codes and perform an engine run to re-check misfire. If misfire returns, proceed.
- Swap the ignition coil from cylinder 4 with another cylinder’s coil; if misfire follows the coil, replace the coil
- If coils are suspected good, swap the fuel injector with another cylinder; if misfire follows the injector, replace injector or service as required
- Measure injector pulse width and verify injector is firing electrically; if pulse width is present but no fuel flow, inspect or replace injector
- Perform a compression test and/or leak-down test on cylinder 4; if compression is low relative to others, diagnose internal mechanical issues (valves, piston rings, head gasket)
- Check fuel pressure and filter; ensure adequate system pressure and no leaks; correct fuel delivery issues
- Use an oscilloscope to verify ignition primary/secondary waveforms and cam/crank sensor signals; repair wiring, sensors, or timing issues as required
- Inspect for intake manifold leaks or vacuum leaks at cylinder 4; repair gaskets or hoses if needed
- If all subsystem tests pass (ignition, fuel, compression, wiring), consider ECM/ignition driver failure and consult factory procedures before replacement
- After repair, clear codes and perform a drive cycle to confirm no recurrence and verify good fuel trim and O2 responses
Likely causes
- Faulty ignition coil on cylinder 4
- Worn or fouled spark plug in cylinder 4
- Faulty fuel injector or injector electrical connector for cylinder 4
- Low compression or valve problem in cylinder 4
- Wiring/connector issue to coil or injector for cylinder 4
Fault status
Status
ECM detected a misfire on cylinder 4 and stored DTC P1204. The MIL may be illuminated. Continued driving with a cylinder misfire can increase emissions and may damage the catalytic converter.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email