The 0420 code is the Catalyst Efficiency Below Threshhold usually triggered when you have a highflow exhaust, removed the cat, and/or have a bad O2 sensor. What it means is that the O2 sensor at the rear is showing above normal levels of hydrocarbons and sends this back to the ECU in a higher voltage. Sometimes I have seen this when the car has an aftermarket exhaust and the person does alot of highway cruising. The extended cruise allows the O2 to have small and slow fluctuations and the ECU thinks something is wrong, then turns on the Service Light. I would take it into the dealer and they can determine if you have a bad O2 or something which is contributing to the 0420 code.
Troy
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1992 S13 240SX SE Fastback KA24DE 5 spd - Type X Aero & Seibon Carbon Hood & Hatch -soon GT28RS
1993 U13 Altima SE KA24DET 5 spd w/ Nismo LSD - A high hp FWD can be fun (GT30R Turbo inside)
1990 Z32 300ZX VG30DETT 5 spd - 600HP & Very Civilized (working on twin GT28RS turbos)
Still trying to import a 1988 R31 Skyline GTS-R w/ RB20DET-R - only 800 produced (legal under show/display regs)
Well, I have the pre-cat removed with the HS header and I have an o2 sim that needs to be installed. The cat had been gone for about 3 weeks before that code finally showed up. The 0037 code for an error with the second o2 sensor went away when this one popped up.
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Even Ice Cube calls me an OG. Ez-E would, but well, you know....he had relations with Mike Young.
When you install the sim, that will go away. Strangley enough, I have both o2 sensors in my header before the secondary cat, with my new hotshot, and I haven't thrown a code in over 1000 miles... knock on wood.
Well, I have the pre-cat removed with the HS header and I have an o2 sim that needs to be installed. The cat had been gone for about 3 weeks before that code finally showed up. The 0037 code for an error with the second o2 sensor went away when this one popped up.
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