CEL comes and goes....

[uwbradley]

Hey,

Not too long ago, I took my Navajo in to get the check engine light looked at. They scanned it and told me it was throwing a code 40/41. They said to change the MAF and the 02 sensor, to the tune of 400 bucks. I cheerfully declined, and did the work myself.

I did the work, and within an hour of changing the sensors the CEL came back on again. However, it does not always stay on. If I am driving on the freeway, it won't turn on until I start to drive in the city, and if I drive in the city first and then get on the freeway it will eventually shut off, until I start to city drive again.

When I pulled the 02 sensor, this thing was carbon caked. I mean, it was a black nub sitting on the end of the sensor, with no way that exhaust could pass through it. I was wondering if the Cat has been clogged with this same crap and is now throwing the CEL, considering exhaust gases would have a hard time passing through the carbon loaded cat, and giving the sensor innacurate readings.

What do you think?

Brad

 

[Alec]

An OBDI code reader is $25 at Walmart, I suggest getting one of those and seeing if it's still the same code.

 

[Zulu95]

According to my 2003 Autodata OBD II Code book code 40 is O2 sensor 1, bank 1 swapped with O2 sensor 1, bank 2.
Code 41 is O2 sensor 2, bank 1 swapped with O2 sensor 2, bank 2.
The CEL may not be for the same reason. A number of people have posted being able to get free "reads" at Autozone and the like. I would be looking to find out for sure what is wrong before spending anymore cash!

 

[MrShorty]

A fouled CAT could maybe cause the CEL to come on, but that doesn't address the how it got clogged. When the O2 sensor is known to be good, the next step in the "circuit pinpoint tests" for any O2 sensor code is to check the fuel pressure. Make sure the fuel delivery is correct.