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99 Honda Odyssey P0304 & P0305 Misfire with P1399 Code: How to Diagnose and Fix Using Coil Drop Test

Model: 99 Honda Odyssey Fault Code: P0304 Posted: 2011-03-29 02:50

When experiencing misfire codes like P0304, P0305, or the generic P1399 on a 1999 Honda Odyssey, follow this proven diagnostic sequence from cheapest to most expensive: 1. Perform the ignition coil drop test: While the engine is running, disconnect each coil pack one at a time and observe if there's a noticeable change in engine performance or RPM. If the engine runs smoother or shows improved stability when a specific coil is disconnected, that cylinder is likely faulty — replace the corresponding coil. 2. Check for EGR-related issues: While an EGR valve malfunction can cause misfires, on Honda Odysseys (especially 1990s models), a clogged EGR port is more common than a failed valve itself. If the P1399 code appears alongside other random misfire codes (P0300-P0306), this should be investigated first. 3. Catalytic converter replacement: Only consider replacing the catalytic converter as a last resort. A P0420 code (catalyst efficiency) may actually stem from an underlying coil issue rather than a failing converter, since both symptoms — rough idle and misfires — are identical. Key insight: In many cases, one faulty ignition coil can trigger multiple misfire codes across different cylinders due to poor spark delivery. The drop test is more reliable than resistance testing of plug wires or coil leads (e.g., measuring 1.7M vs 3.2M ohms), as it directly evaluates engine response. Real-world examples confirm this: Users with 99-02 Honda Odyssey models have successfully resolved P0304, P0305, and P1399 by replacing a single ignition coil — often cylinder #2 or #6 — after confirming no improvement in performance when disconnected. After replacement, engines run smoothly and codes clear. Tip: Always start with the drop test before investing in expensive repairs or parts replacements.

Related fault codes
P0304P0305P1399
Comments (13)
Anonymous 2011-03-29 05:26

On most Honda Odysseys, especially from the 90s era, EGR-related issues are typically caused by clogged ports rather than a failed EGR valve. This is important to note when diagnosing P1399 or random misfire codes.

Anonymous 2011-11-25 17:26

Last week my '02 Honda Odyssey (197K miles) began vibrating noticeably on the highway, especially under load. I pulled over and noticed the vibration intensified when accelerating. After limping home, I used an OBD2 scanner and found a P1399 code. Following this thread, I tested each coil using resistance checks — one coil (#4) showed abnormal readings (1.7M vs 3.2M ohms). However, the drop test pointed to coil #2 as the culprit. After replacing coil #2, the engine ran smoothly immediately. This was a much faster fix than relying on resistance measurements alone. Thanks for this clear guidance! — Honda User MAN

Anonymous 2013-02-03 09:21

I performed the drop test and found cylinder #6 wasn’t responding. After replacing the coil, the issue persists — no change in RPM when disconnected. This suggests a possible faulty fuel injector or internal engine problem rather than just a bad coil.

Anonymous 2013-02-03 14:54

Please start a new topic for your specific situation to get more targeted advice and avoid mixing unrelated issues.

Anonymous 2013-04-09 14:37

I recently had the same issue with my 2000 Honda Odyssey — rough idle, multiple misfire codes (P0300, P0302, P0304, P0305, P0306), and a persistent vibration. I checked fuel pressure (65 psi), compression (160 psi across all cylinders), and spark plugs — all were fine. Initially, I suspected the crankshaft position sensor due to widespread misfires. After reading this thread, I realized one faulty coil could cause multiple codes. I now plan to perform a drop test to isolate the problematic cylinder. Thanks for the insight! This is exactly what helped me shift my diagnosis from guesswork to a systematic approach. I’ll update with results later — and I’m grateful to find such practical, no-cost troubleshooting resources here. I truly appreciate this community's focus on simple, cost-effective fixes over expensive dealership repairs.

Anonymous 2013-04-10 03:59

The drop test confirmed coil #2 was burnt out. After replacing it, the engine ran smoothly and all codes cleared. This is solid proof that a single faulty ignition coil can trigger multiple misfire codes — thank you to everyone for this clear, actionable solution! I’ll be visiting this forum more often in the future. Simple fixes, hands-on advice — exactly what I need as a DIYer.

Anonymous 2013-07-31 15:53

I was driving my 2000 Honda Odyssey to Vegas when it started shaking about 41 miles from destination. I checked tires (recently replaced) and found no issues. The vibration worsened with acceleration, and the check engine light came on. I took it to a Discount Tire shop — they referred me to a local mechanic who performed spark plug, fuel injector, air intake, EGR valve, and one coil replacement for $700. Afterward, the vibration remained. When I replaced tires again, the issue persisted. On my return trip, the vibration returned intermittently and the CEL flashed under load. The vehicle is still under Firestone warranty — I’ll update once it’s resolved. This experience highlights how tire specialists may miss deeper engine issues like misfires or sensor faults.

Anonymous 2013-07-31 16:33

TITO — please start a new topic for your issue. You’ve already had multiple services (tires, spark plugs, EGR, coil) with no resolution and a flashing CEL. This strongly suggests an underlying engine problem. A tire specialist is not equipped to diagnose such issues. Please consult a qualified mechanic or technician. Keep monitoring the check engine light — if it continues to flash under load, that’s a serious warning sign. Let us know for further advice.

Anonymous 2014-02-04 19:34

I have a 2000 Honda Odyssey and recently experienced misfiring with multiple codes (P0300, P0302, P0304, P0305, P0306). I avoided the drop test initially due to fear of causing further damage. Instead, I simply replaced one coil pack — but after swapping it with a known good unit and testing, the issue remained. Eventually, when I swapped out cylinder #2’s coil, the engine ran smoothly again. This experience confirms that a single faulty ignition coil can cause multiple misfire codes. Thanks to all who shared this solution — I wish I had found this forum sooner!

Anonymous 2014-02-04 19:38

Thanks for sharing your successful fix, Jeremy. It’s great to see real-world results from a simple, cost-effective approach.

Anonymous 2014-03-07 21:32

I’m experiencing the same issue — any success stories or troubleshooting tips for P0304 and P0305 on a 99 Honda Odyssey?

Anonymous 2014-03-08 13:08

Molly, please start a new topic with your full vehicle details so we can provide more accurate advice.

Anonymous 2014-05-16 00:19

Success! I have a 1999 Honda Odyssey with 81,000 miles. It started misfiring on Monday and the check engine light came on. After scanning, I saw P0300, P0301, P0302, and P0306 — plus P1399. Following this thread, I performed a drop test and found cylinder #6 was the issue. I ordered a Delphi GN10168 ignition coil ($38) from Amazon and replaced it in under 10 minutes. The engine now runs smoothly. I expect the check engine light to clear by tomorrow when my wife takes it for errands. I’ll also keep one spare coil on hand — as my 2002 Acura CL uses the same coil pack.