2001 Honda Accord

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#1
Error Code P0420 Cat eff. below threshold (Bank 1)

4 cyl. V-tec engine, 01 Accord with 220,000 miles.

Should I replace the O2 Sensor in bank one, or is the Cat most likely shot ?

And how would I know for sure?

Can't pass inspection for emissions.
 

Paul

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#2
Are there any other trouble codes besides PO420?Remove the No 13,7.5 Amp fuse for the clock to reset the Pcm and then follow the instructions below.The older Accords,98,99 had troubles with the converters.It may be the newer models like yours have the same trouble.

DTC P0420: Catalyst System Efficiency Below Threshold

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then recheck for DTC P0420.

P0137, P0138: Secondary HO(2)S (Sensor 2)
P0141: Secondary HO(2)S (Sensor 2) Heater

Reset the ECM/PCM.
Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
Except F23A4 SULEV engine: Test-drive at 40 - 55 mph (64 - 88 km/h) for approx. 2 minutes . Then decelerate for at least 3 seconds with the throttle completely closed. Then reduce the vehicle speed to 35 mph (56 km/h ), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result. F23A4 SULEV engine: Test-drive at 50 - 55 mph (80 - 88 km/h) for approx. 2 minutes . Then decelerate for at least 4 seconds with the throttle completely closed. Then accelerate to 55 mph (88 km/h ), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result. Is the test result FAIL? YES - Check the three way catalytic converter (TWC). If necessary, replace the TWC. NO - Intermittent failure, system is OK at this time.

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