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
2,310

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.

2 out of 2 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
905

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 68,348 nationwide Civic listings starting at $700.
ZIP:

Search Honda Civic Questions

Honda Civic Experts

#1 Takoda Fraser
Takoda Fraser
Reputation 850
#2 Tom Demyan
Tom Demyan
Reputation 700
#3 Jonathan Ford
Jonathan Ford
Reputation 520
View All

Related Models For Sale

Used Nissan Sentra"
460 Great Deals out of 36,448 listings starting at $1,250
Used Toyota Corolla"
729 Great Deals out of 53,234 listings starting at $1,495

Used Cars For Sale

2015 Honda Civic For Sale
45,779 listings starting at $20,995
2014 Honda Civic For Sale
36 Great Deals out of 2,937 listings starting at $13,999
2013 Honda Civic For Sale
100 Great Deals out of 2,746 listings starting at $12,000
2012 Honda Civic For Sale
263 Great Deals out of 6,631 listings starting at $8,900
2011 Honda Civic For Sale
28 Great Deals out of 694 listings starting at $7,995