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2001 Honda CR-V P0420 and Cylinder Misfire Troubleshooting Guide

Model: Honda CRV Fault Code: P0300 Posted: 2019-06-30 12:02

I own a 2001 Honda CR-V with 180,000 miles. The vehicle is showing OBDII error codes: P0420 (catalyst system efficiency below threshold), P0300 (random/multiple cylinder misfire), P0302 (misfire in cylinder 2), and P0304 (misfire in cylinder 4). I've only had the OBDII scanner for a week, so I'm still learning how to interpret the live data. I'd like to understand how to narrow down the root causes of these issues. Specifically: - How can I determine if the misfires are occurring at idle or under load? - What does freeze frame data reveal about when and under what conditions these errors occur? - Is there a correlation between P0420 and cylinder misfires? I've attached photos of both freeze frame and live data, and fuel trim readings appear to be within normal range (-10 to +10 at all RPMs). However, the vehicle exhibits rough idle and difficulty starting. I'm also concerned about a flashing check engine light during driving, which may indicate a hard misfire. Any guidance on diagnosing spark quality for the affected cylinders (especially cylinder 2 and 4) would be greatly appreciated. Possible causes include faulty spark plugs, worn ignition wires, or distributor issues. Please advise if further diagnostics are needed.

Related fault codes
P0300P0420
Comments (6)
Anonymous 2019-06-30 13:38

Please share your fuel trim values at idle, 1500 RPM, and 3000 RPM. Look for readings between -10 to +10 across all speeds. Hold the engine at each speed for at least 20 seconds to get stable data. Also check the freeze frame data when errors occur — this shows exact conditions (e.g., load, temperature) when P0420 or misfire codes triggered. P0420: The B1S2 oxygen sensor monitors catalytic converter efficiency. If it oscillates between 0.2V and 0.8V, the catalyst is likely faulty. For P0302 and P0304, refer to established troubleshooting threads on this forum for common causes and fixes. A flashing check engine light while driving indicates a hard misfire — avoid driving under these conditions as it can damage the catalytic converter or worsen emissions issues. Do not attempt to drive if this is happening.

Anonymous 2019-06-30 13:47

I've uploaded photos of the freeze frame data showing when and under what load each error code occurred.

Anonymous 2019-06-30 13:49

Attached are live data readings from idle to 3000 RPM, including fuel trims and oxygen sensor values.

Anonymous 2019-06-30 14:57

Fuel trim readings appear normal across all RPMs. The misfires seem to occur at idle and under load. Does the check engine light flash during driving? If so, this points to a hard misfire. Verify spark delivery to cylinders 2 and 4 using a scope or spark tester. Poor or no spark may indicate faulty ignition wires, distributor issues, or worn spark plugs. Confirm that spark plugs are in good condition and properly gapped. Please update with your findings so we can assess next steps.

Anonymous 2019-06-30 16:35

I ran the OBDII scan again after driving for approximately 30 minutes. The vehicle still shows rough idle and struggles to start, especially in cold weather. I apologize for posting multiple photos — they were meant to provide a clearer picture of the data.

Anonymous 2019-06-30 16:36

This post references a technical term related to fuel trim behavior under load — I'm not sure what it means or how it applies here. Could someone explain its relevance to P0420 and cylinder misfires?