1998 Accord ---- P0420 and P0401 related??
#1
02-14-2018, 10:49 AM
1998 Accord ---- P0420 and P0401 related??
Just something I observed... My daughter has a 1998 Accord, 4Cyl, auto trans. 225,000 miles
I bought this car for my daughter about 6 years ago. After about a year, the P0420 Catalyst System Efficiency Below Threshold popped up ( SEL on). This would ONLY come one when she was driving over 45 MPH. I decided to clear it and see what happens. Yea for 5 years I did this over and over since we only had to do this when she drove on the highway.
Fast forward to 2 weeks ago, the SEL light came on and Presto! a NEW code - P0401 EGR Insufficient Flow along with the P0420. I took the upper intake manifold off and cleaned the EGR port (you will see a thread I did on this earlier).
It has been 2 weeks now and I know my daughter drove on the highway several times and NO more codes! The "Bad Catalytic Converter" is no longer a problem!
So, I wonder if you get the P0420 code, and it only comes on when you drive 45 MPH or faster (and your car has high mileage), maybe you should check the EGR ports? Better to do it yourself for $20 than spend $300-$500 on a new CAT.
I bought this car for my daughter about 6 years ago. After about a year, the P0420 Catalyst System Efficiency Below Threshold popped up ( SEL on). This would ONLY come one when she was driving over 45 MPH. I decided to clear it and see what happens. Yea for 5 years I did this over and over since we only had to do this when she drove on the highway.
Fast forward to 2 weeks ago, the SEL light came on and Presto! a NEW code - P0401 EGR Insufficient Flow along with the P0420. I took the upper intake manifold off and cleaned the EGR port (you will see a thread I did on this earlier).
It has been 2 weeks now and I know my daughter drove on the highway several times and NO more codes! The "Bad Catalytic Converter" is no longer a problem!
So, I wonder if you get the P0420 code, and it only comes on when you drive 45 MPH or faster (and your car has high mileage), maybe you should check the EGR ports? Better to do it yourself for $20 than spend $300-$500 on a new CAT.
#2
02-14-2018, 06:21 PM
Iti's possible the two are related, but no way to know. None of the shop manuals specify the conditions leading to P0420. It is known that post cat O2 sensor voltage oscillation (0.1-0.9v) in a regular pattern similar to pre-cat O2 sensor will trip the code. However some oscillation iis normal and no specs exist such as X zero-xings per minute or similar.
Recently I got code P0430 on Acura MDX V6 and observed frequent (1-2 hz) oscillations in the post-cat O2 sensor at idle. I decided to install an anti-fouler fix for the light but found there was insufficient room for the stackup. On installation of a new O2 sensor (broke old sensor during removal), the P0430 was erased and has not returned.
good luck
Recently I got code P0430 on Acura MDX V6 and observed frequent (1-2 hz) oscillations in the post-cat O2 sensor at idle. I decided to install an anti-fouler fix for the light but found there was insufficient room for the stackup. On installation of a new O2 sensor (broke old sensor during removal), the P0430 was erased and has not returned.
good luck
#3
02-15-2018, 02:33 PM
Like Texas Honda said, I don't think the 2 are completely related. Yes, both work with the exhaust side of the engine, but are separate. When my wife's Accord coughed up a PO401 code (EGR), it was the port and the valve. But when my 99 Accord coughed up a PO420 code, it was the cat. So that's 2 cars with 2 different codes that had 2 different solutions.
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