Jim Grant's Tech Tips
'00 Nissan Sentra, Check Engine Light W/code P0420
Q: The Check Engine Light on my 00 Nissan Sentra came on. I took my car to Autozone for a computer check. They told me the computer gave an OBD II code of P0420. Just what does that mean?
A: The On-Board Diagnostic (OBD) is a second generation (II) of vehicle computer systems found on most 96 and new vehicles. The OBD II code # P0420 is the computer in your vehicle reporting that the Catalyst system efficiency is below the allowable threshold. In real world terms? It means your catalytic converter is not working correctly and your vehicle may be producing excessive exhaust emissions. Just because your computer is reporting this code, dont just run out and replace the converter. Your vehicle has a sensor at the rear of the converter that is used by the computer to monitor the converter. In some cases we have found that this sensor passes the test the computer runs on it, but fibs enough to cause the computer to report that the converter is not working properly. At the price of the converter on your vehicle you may want to have some diagnostics performed before you replace any parts.