what is engine code p0420

hondagreen
0

Asked by hondagreen May 25, 2013 at 02:12 PM about the 1994 Honda Civic

Question type: Maintenance & Repair

5 Answers

DavidH25
Not Active

Catalytic Convertor and/or downstream O2 sensor issue. Some forums and other websites say the O2 sensor is not involved, others do, but what they all agree on is the cat. "Below Efficiency Threshold"

1 out of 1 people think this is helpful.
Michael Mierzejewski
2,540

Correct. The rear oxygen sensor is telling the computer that the catalytic converter is not working efficiently enough. So really it could be either part. Thise problem is best diagnosed by someone with a professional level scan tool as it requires reading the waveform and switching rate of the oxygen sensor. Of course if you dont mind spending money, you could just replace the rear oxygen sensor itself and hope thats it.

3 out of 3 people think this is helpful.
John Surovik
125

P0420 is simply "cat efficiency below threshold" Borrow a scan tool that has the appropriate obd1 connector for the car, and look at the PID data. You should see the voltage fluctuate from like .1v to.9v on a working sensor. IF YOU ARE RUNNING AN AFTERMARKET CATALYTIC CONVERTER OR TEST PIPE, YOU WILL THROW THIS CODE... If that is the case, simply search on a site like passwordjdm.com for a mechanical o2 sim. That will fix that issue.

1 out of 1 people think this is helpful.
Best Answer
Bradley Shelledy
1,055

Catalyst System Efficiency Below Threshold (Bank 1) you can look up more info on http://www.obd-codes.com/p0420 this will give you afew things to look at for possible causes and will give you some ideas of where to look to fix it.

1 out of 1 people think this is helpful.
hondagreen
0

My first time using Car Gurus! You guys are awesome and I really appreciate the feedback.

Your Answer

Add photo

Related Questions

Civic
Looking for a Used Civic in your area?
CarGurus has 59,378 nationwide Civic listings starting at $995.
ZIP:

Search Honda Civic Questions

Honda Civic Experts

#1 Takoda Fraser
Takoda Fraser
Reputation 890
#2 Tom Demyan
Tom Demyan
Reputation 770
#3 Jonathan Ford
Jonathan Ford
Reputation 630
View All

Related Models For Sale

Used Honda Accord"
1,078 Great Deals out of 72,117 listings starting at $1,200
Used Toyota Corolla"
855 Great Deals out of 53,407 listings starting at $1,998
Used Honda Civic Coupe"
238 Great Deals out of 12,896 listings starting at $1,999
Used Toyota Camry"
1,239 Great Deals out of 77,184 listings starting at $800
Used Nissan Altima"
1,022 Great Deals out of 70,787 listings starting at $700
Used Nissan Sentra"
459 Great Deals out of 38,959 listings starting at $1,495
Used Volkswagen Jetta"
598 Great Deals out of 30,128 listings starting at $1,395
Used Hyundai Elantra"
578 Great Deals out of 45,169 listings starting at $1,480
Used Ford Mustang"
771 Great Deals out of 31,720 listings starting at $1,800
Used Acura TL"
277 Great Deals out of 6,446 listings starting at $1,990
Used Toyota Tacoma"
510 Great Deals out of 21,704 listings starting at $1,900

Used Cars For Sale

2015 Honda Civic For Sale
18 Great Deals out of 37,304 listings starting at $15,925
2014 Honda Civic For Sale
60 Great Deals out of 1,988 listings starting at $12,559
2013 Honda Civic For Sale
124 Great Deals out of 3,643 listings starting at $10,471
2012 Honda Civic For Sale
227 Great Deals out of 6,214 listings starting at $6,960
2011 Honda Civic For Sale
28 Great Deals out of 664 listings starting at $7,561