Originally Posted by Vladi17
The code states that "Catalyst System Efficiency Below Threshold", I was told this was a problem with the o2 sensors from reading other forums. Problem seemed to go away after I replaced the sensors but then came right back months later. What should I do??
Oh yeah, its also automatic. Same year as yours too (1998)
Well Andrew, I think the only way that P0420 would come on and an O2 sensor would be the cause would be if there was another trouble code such as P137 or P141 indicating an O2 sensor problem, which would trick the computer into thinking that the catalytic converter wasn't doing its job and thus setting off P0420. My PO420 has been on for the past few months and I'm 95% sure it's the cat. I really need to replace that.
DTC P0420: Catalyst System Efficiency Below Threshold
1) Reset the ECM/PCM.
2) Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
3) 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.
So if P0420 comes on and it's the
only code, either replace the TWC or have your Honda dealer (or someone else) test the TWC to see if it's bad or not. If there are multiple DTCs, troubleshoot those first. I only have P0420
I'll copy this in the DTC thread.