2004 Hyundai Sonata GLS V6 Misfire Codes P0300/P0302/P0304/P0306: Does It Have an Ignition Failure Misfire Sensor?

The 2004 Hyundai Sonata 2.7L V6 does not have an 'Ignition Failure Misfire Sensor.' Instead, it uses knock sensors to detect engine knocking and adjust ignition timing. These sensors are typically located on the cylinder head near each cylinder. Since your car is a DOHC V6 with multiple misfires in cylinders 2, 4, and 6 (all on Bank 2), it's likely not a sensor issue but rather a mechanical or valve timing problem. Check RockAuto.com for accurate parts diagrams of knock sensors for this model.

Thanks for the clarification! I didn't realize the V6 uses knock sensors instead of an ignition failure misfire sensor. The issue is that I only see misfire codes when driving — they appear and disappear intermittently, with no visible engine performance loss until the light comes on. After that, the car runs poorly and recovers after a few miles. This pattern suggests a dynamic misfire, possibly related to valve timing or fuel delivery under load.

Are you experiencing intermittent misfires only when driving at higher speeds or under load? If so, that could point to a valve timing issue on Bank 2, especially since cylinders 2, 4, and 6 are all affected.

Yes — the car runs smoothly until the check engine light comes on. At that moment, it loses power and misfires in cylinders 2, 4, and 6. I pull over, check the codes (still P0300/P0302/P0304/P0306), clear them, and resume driving. The car runs fine again until the light comes back on after 30 to 75 miles. Sometimes, while driving, the light turns off by itself, and power returns immediately. I've tested cylinder compression (125–130 psi) for cylinders 2, 4, and 6 — all within range. Head gaskets are intact, timing belt was replaced one year ago and checked recently as 'like new.' I'm now considering a valve timing test on Bank 2 to rule out mechanical misalignment.

The car runs perfectly until the check engine light activates. Then, it begins to lose power and misfire in cylinders 2, 4, and 6. I've replaced all major components — spark plugs, coils, injectors, gaskets — and the codes persist. This strongly suggests a deeper mechanical or timing issue rather than an electrical one.

A valve timing issue on Bank 2 could be causing intermittent misfires in cylinders 2, 4, and 6. Even if the timing belt is intact, the exhaust cam (which is driven by a chain separate from the intake) may not be properly synchronized at certain engine speeds. A technician should verify the valve train timing specifically for Bank 2 using a scan tool or mechanical inspection.

My car is a 2004 DOHC 2.7L V6 — it runs great, no smoke, no oil consumption, and has strong power. The check engine light only comes on intermittently (every 75–125 miles), and only during driving. When the light activates, misfires appear in cylinders 2, 4, and 6. I've tested all three cylinders — compression is solid at 125–130 psi. Head gaskets are fine, timing was checked and deemed correct. The car runs well until the light comes on, then performance drops. After a few miles, it may recover automatically. This behavior suggests a dynamic misfire, not a constant one. If it were a full timing issue, I'd expect consistent poor performance — but instead, it only occurs under certain conditions. I'm now considering taking it to another shop for a dedicated valve timing test without mentioning the misfire codes.

The timing belt synchronizes the crank and intake cams, but the exhaust cam is driven by a chain that's timed off the intake cam. This means valve timing on Bank 2 can vary with RPM — if it's slightly off at certain speeds, it could cause misfires in cylinders 2, 4, and 6. A Hyundai technician should perform a precise valve timing check on Bank 2. An hour of diagnostic testing is often cheaper than replacing parts like cam chains or timing components.

Update: I had the timing belt checked today — it's in excellent condition and was confirmed as 'like new.' The technician said no replacement needed. However, the check engine light still comes on every 75 to 125 miles with misfire codes P0300, P0302, P0304, and P0306. I've replaced everything else — the car runs great otherwise. I'm now completely stuck. It has a lot of power and drives well, but the light keeps coming back. I'm considering taking it to another shop for a valve timing test without disclosing the misfire codes first.

Even if the timing belt is in good condition, the valve train timing on Bank 2 should still be verified — especially since only cylinders 2, 4, and 6 are affected. Was a full diagnostic performed that included analysis of misfire causes? If so, could you share the technician's report or findings? This would help determine whether it's a mechanical issue or something else like fuel pressure fluctuations.

I only see misfires in cylinders 2, 4, and 6 — not all at once. Sometimes the car runs fine for hours, then the light comes on with those codes. I clear them and can drive up to 300 miles before they return. The timing was checked and deemed okay by a technician. I've tested cylinder compression (125–130 psi) — all good. I'm now planning to take it to another shop for a valve timing test, and I won't mention the misfire codes upfront to see if that resolves the issue.

This is a challenging problem to diagnose without being able to reproduce the condition under controlled conditions. If you're able to get it tested at a shop, please share your results — especially any findings related to valve timing or sensor readings.