Service Engine Light on 2006 Nissan Altima

My Altima has 117K miles, and I am the orginial owner, and recently the “service engine” light has illuminated. It shines and then stops shining. It may shine for several days then stops for several days. A service center where I buy tires and basic fluid changes said the oxygen sensor was okay but there may be some issue with the catalytic converter. They believe there may be some “pressure” in the converter and recommended I take it to an exhaust speciality service center.

I’ve never heard of this problem in my 45+ years of car ownership. Can you shed some light on this idea of a problem with the catalytic converter and the “service engine” light.

We can’t shed light on the problem unless you’re able to give us the diagnostic code(s). These codes will be something like a P0XXX or a P1XXX.


These days a lot of the functions of a car (e.g. how much fuel to send into the engine) are controlled by a computer. That same computer uses a whole bunch of different systems of sensors to collect information about what the car and its systems are doing. E.g. you have a Mass Airflow (MAF) Sensor that tells the computer how much air is flowing into the intake and that is one of the things that goes into how much fuel the computer will send to the cylinders.

Anyway, when the computer gets readings from one of these systems that are outside of specifications (or perhaps no reading at all) it turns on the check engine light and it stores “Diagnostic Trouble Codes” (DTCs) in the computer’s memory. There are little scanners that you hook up the car to read the DTCs.

The thing is that there are hundreds of DTCs. Some of those would tell a mechanic to check out things like oxygen sensors and/or catalytic converters. But other codes would have nothing to do with it.

If you can post the exact codes here people can give you some advice about what kinds of things ought to be done. The format of the codes will be P0123. Presumably your shop scanned the computer and found codes. These might be written on your invoice or you they might have a record if you call them. Alternatively, if you’re not in California, many auto parts chain stores will read your codes for free. Get the codes and report them here (exact codes like P0123).

For more info, I have always found this to be a useful site: (OBD stands for “On Board Diagnostics” - as of 1996 we are all on OBD-2)

I susprct you are talking about a CEL (Check engine light) not a SEL (Service Engine Light)which maya be trying to tell you it is due for an oil change.