$3 O2 simulator fix for P0420 Check Engine Light

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  • 3 Years Ago
Do you occasionally get code P0420 - catalytic converter low efficiency? This $3 electrical circuit may fix the problem permanently by electrically smoothing out the o2 sensor output. Don't spend $10 on fuel additives (tried it), or $100 on new o2 sensors (tried it), or $200-400 on a new non-OEM catalytic converter which may fail again (seen lots of posts by Honda owners who say they don't last). You'll see how to test both o2 sensors on a bench with a propane torch - if either has failed you should replace it and see if that fixes the problem. I replaced mine before I knew how to test it and it solved the problem for a short while but it came back. If you have a graphing ODB scanner I show how to graph the o2 sensors to see if the catalytic converter is working. You can try simpler ODB readers such as ScanGuage but the data is supposed to change from 0V-1V every second so you really need a graphing tool (Harbor Freight 98614 / 60693 is $120 but often $80). I also tried to use a multimeter hooked into the o2 sensor with wires but I found that also too hard to really see what's happening. Once you verify from the o2 sensors that the catalytic converter isn't functioning efficiently, I show you how to modify the downstream sensor #2 mounted on or after the catalytic converter with a simple Resistor Capacitor (RC) low-pass filter to smooth out the signal by removing "high frequency" (faster than 5 seconds) changes in the o2 levels . There is an alternative using spark plug defouler/unfouler to pull the o2 sensor back from the exhaust stream, but it's unclear if this will work or for how long. The computer P0420 is strictly determined by whether the downstream sensor #2 is crossing the .5V threshold a lot less than sensor #1, so an electrical solution addresses this directly. This method may not work if your o2 sensor is too far gone, in which case you can buy a 555 timer based o2 simulator which generates a signal independent of the o2 sensor output, but that costs $20-40 and you have to mail order it. This $3 solution is easy if you're good with a soldering iron and worth a try. Here's a link to one of the internet posts on how to build the RC low-pass filter: http://www.wazees.com/media/4324/02-mil.pdf Here's a video about o2 sensors and P0420 but I tried his diagnostics and they were difficult. He uses a basic OBD scanner and it's just not quick enough. It encouraged me to buy the graphing scanner and I'm glad I did so I could verify my fix works, although you don't have to. He also tried diagnosing it with the temperatures, which I also did, but my results were inconclusive: http://www.youtube.com/watch?v=9VZ5K8n5jj0 Here's an excellent video on how to bench test an o2 sensor. If yours is bad I think you want to replace it, especially if it's the upstream sensor since that's going to affect how rich/lean your engine is and may cause damage to a catalytic converter. If it's the downstream sensor that's broken then my fix may work on it - it depends on how it's broken. o2 sensors cost $100, and this fix is a lot cheaper than replacing the sensor, so I'd try this before replacing the downstream sensor. http://www.youtube.com/watch?v=stFhLSHsOGg Finally here's an excellent video on how to use the spark plug defouler/nonfouler. My biggest gripe is that I couldn't find any reports on the internet to support that this actually works most of the time or that it lasts. Some of you who are more comfortable with a drill vs soldering iron might want to go this route. You can find the parts at Autozone for $10. I suppose if you mail order them you can maybe do it for $5. Half my motivation for doing this DIY is because mail ordering parts (spark plug defouter or 555-based o2 simulator) is inconvenient. http://www.youtube.com/watch?v=GqDmmLQ4pGk