The catalytic converter closest to the cylinder head can fail causing illumination of the Check Engine Light. Prompt repair of this problem is recommended because the catalyst material can be sucked into the engine and cause internal damage.Google+
Car Problem Reports
Nissan Sentra Check Engine Light Due to Failure of Catalytic Converter Closest to Cylinder Head
Nissan Sentra Problem
Exhaust & Emissions Affected: 2.5L 4 Cylinder
Average Mileage: 120,823 mi (59,645 mi - 185,331 mi)
Visitor, 2008 Nissan Sentra, 141,000 mi
Check engine light, loud knocking - told it was a bad cat
Visitor, 2005 Nissan Sentra, 119,500 mi
Had a fuel system cleaning done which set the check engine light off. Turned out to be the front catalytic converter for precisely the reason stated. Fixed through replacement.
Visitor, 2007 Nissan Sentra, 125,000 mi
Check engine light came on and my mechanic reset the codes and advised me to pump premium gas for the new few fills. Did so and the check engine light stayed off for 6 months. Now its back and he is advising me about a bad cat and that I need to replace it for $850. He reset the codes and advised me to replace it the next time the check engine light comes on.
Visitor, 2008 Nissan Sentra, 114,500 mi
Intermittent check engine light. Dealer and alt repair shop advised bad cat. Took to a third shop for full breakdown of exhaust system and found cat split at the welds. Mechanic quote, "Robot did not have its coffee that day". Replaced at cost of 983.00. Core sent back to Nissan or would be charged another 140.00.
Visitor, 2008 Nissan Sentra, 91,860 mi
Took my vehicle in for service. I had the coolant line flushed and fuel line flushed and diagnostic code check. The service engine soon light was on when I took it in and then the mechanic reset it. He told me the diagnostic code was a result of the catalytic converter going bad. Well, the light just came back on.
Visitor, 2010 Nissan Sentra, 62,572 mi
3rd cylinder bad. Had to have entire engine replaced. Nissan refused any help because it was out if warranty at 60,000.
Visitor, 2008 Nissan Sentra, 145,350 mi
I am about to go on a 2,000 mile road trip and this is come on. I passed emissions today but gave the the Catalytic Converter error message. I am getting checked out tomorrow by the dealership and I hope I do not have to replace anything.
Visitor, 2006 Nissan Sentra, 59,645 mi
Code p 420 service engine soon
Visitor, 2008 Nissan Sentra, 110,000 mi
Catalytic Converter failure
Visitor, 2008 Nissan Sentra, 140,000 mi
I was told that the CO2 sensor is either broken or just malfunctioning, but my service engine soon light keeps coming on and off.