Service Engine Light

Asked by Oct 30, 2016 at 06:23 PM about the 2007 Nissan Altima 2.5 S

Question type: Maintenance & Repair

I just got a used 2007 Altima. The service engine
light is on again. We just had both catalytic
converters changed, oil change, and there was a
vacuum hose replaced. Now the light has come on
again. I took it to the auto parts store and the code
this time is: PO420. Can you help?

2 Answers


Read through the possible causes. http://www.engine- good shop will be able to diagnose the exact issue. Sounds like your not so lucky.


Did the shop clear the computer after the catalytic converters were replaced? They should have. Did they put the correct converters on your vehicle? If you have California Emissions and they put Federal Emissions converters on it that will do that. Did they properly warm up the new converters before they gave the vehicle back to you? If not, damage will occur to the new converters. Putting on the wrong converters or not warming up the new converters is on the shop. They should be made to fix it and eat any costs involved. There may be a problem with the downstream oxygen sensor(s). This trouble code sets when the computer sees too much fluctuation in the signal from the downstream oxygen sensor(s). The signal is supposed to be very close to a flat line. What I'd suggest is clear the computer and drive for a few days with the gas tank between 3/4 and 1/4 full. This will allow the computer to run the diagnostics on the catalytic converters. If the trouble code does not come back you should be good to go. If it does return you'll need a shop with a scan tool that can view the signals from the downstream oxygen sensors live while the vehicle is being driven for proper diagnosis. HTH. -Jim

Your Answer

Nissan Altima Experts

  • #1
    Tom Demyan
  • #2
  • #3
    Cassie Sapphire
View All

Related Models For Sale

Used Nissan Maxima
265 Great Deals out of 22,818 listings starting at $1,499
Used Honda Accord
1,022 Great Deals out of 57,887 listings starting at $1,099
Used Toyota Camry
927 Great Deals out of 80,593 listings starting at $1,440
Used Honda Civic
752 Great Deals out of 69,404 listings starting at $1,000
Used Nissan Sentra
570 Great Deals out of 52,264 listings starting at $1,995
Used Hyundai Sonata
724 Great Deals out of 50,361 listings starting at $500
Used Toyota Corolla
781 Great Deals out of 53,912 listings starting at $1,200
Used Chevrolet Malibu
978 Great Deals out of 65,934 listings starting at $1,000
Used Ford Fusion
967 Great Deals out of 67,785 listings starting at $1,900
Used Dodge Charger
428 Great Deals out of 28,173 listings starting at $2,490
Used Nissan Altima Coupe
55 Great Deals out of 1,450 listings starting at $2,895
Used Kia Optima
396 Great Deals out of 29,719 listings starting at $2,000
Used Chevrolet Impala
545 Great Deals out of 35,192 listings starting at $900
Used Nissan Rogue
648 Great Deals out of 69,237 listings starting at $2,499
Used Nissan Murano
343 Great Deals out of 25,059 listings starting at $999

Used Cars For Sale

2017 Nissan Altima 2.5 S For Sale
13 Great Deals out of 10,937 listings starting at $12,299
2016 Nissan Altima 2.5 S For Sale
64 Great Deals out of 3,404 listings starting at $9,908
2015 Nissan Altima 2.5 S For Sale
146 Great Deals out of 4,634 listings starting at $8,495
2014 Nissan Altima 2.5 S For Sale
77 Great Deals out of 2,115 listings starting at $3,900
2013 Nissan Altima 2.5 S For Sale
36 Great Deals out of 1,162 listings starting at $5,499

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.