what is engine code p0420

hondagreen
0

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

Question type: Maintenance & Repair

5 Answers

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
3,010

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
135

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.

2 out of 2 people think this is helpful.
Best Answer
Bradley Shelledy
1,225

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.

4 out of 4 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 55,804 nationwide Civic listings starting at $995.

ZIP:

Search Honda Civic Questions

Honda Civic Experts

#1 Takoda Fraser
Takoda Fraser
Reputation 910
#2 Jonathan Ford
Jonathan Ford
Reputation 780
#3 Tom Demyan
Tom Demyan
Reputation 770
View All

Related Models For Sale

Used Honda Accord"
1,227 Great Deals out of 73,105 listings starting at $500
Used Honda Civic Coupe"
262 Great Deals out of 12,837 listings starting at $700
Used Toyota Corolla"
1,234 Great Deals out of 70,971 listings starting at $999
Used Toyota Camry"
1,684 Great Deals out of 89,547 listings starting at $1,500
Used Nissan Altima"
1,698 Great Deals out of 82,484 listings starting at $500
Used Hyundai Elantra"
631 Great Deals out of 56,174 listings starting at $2,490
Used Honda Accord Coupe"
176 Great Deals out of 11,639 listings starting at $2,500
Used Nissan Sentra"
776 Great Deals out of 45,385 listings starting at $1,395
Used Volkswagen Jetta"
533 Great Deals out of 34,453 listings starting at $1,400
Used Hyundai Sonata"
949 Great Deals out of 50,048 listings starting at $999
Used Ford Mustang"
657 Great Deals out of 45,495 listings starting at $1,800
Used Acura TL"
192 Great Deals out of 5,904 listings starting at $1,350

Used Cars For Sale

2016 Honda Civic For Sale
6 Great Deals out of 31,100 listings starting at $16,500
2015 Honda Civic For Sale
110 Great Deals out of 3,416 listings starting at $10,886
2014 Honda Civic For Sale
93 Great Deals out of 2,847 listings starting at $9,995
2013 Honda Civic For Sale
299 Great Deals out of 6,602 listings starting at $8,990
2012 Honda Civic For Sale
96 Great Deals out of 2,584 listings starting at $5,995