So I bought an 02 r53 hatch 6spd with an after market exhaust. It’s throwing an 02 sensor code, but my cel isn’t showing up. The fuse is fine I even replaced it to make sure. Any thoughts why the light won’t come on? All my other gauges work fine

 

I'm gonna go with... It's got no cat and the previous owner had some coding done so that the light doesn't come on for the post-cat O2 sensor code.

 

does the check engine light even come on when you just turn the key on?

 

Good point. The simplest explanation is the most likely.

 

I was doing emissions this week. (Illinois so just checking O2 sensors) and I had two codes P1125 and P1126 but the check engine light did not illuminate. I have always had those codes when the car went into limp mode with an extra code. (Don't remember which one) But it came up on emission but I still passed but it is possible to have codes without the check engine light being on.

 

You can have codes stored in the ECU that won't pop a CEL, they are generally either stored as Pending fault codes (likely to grow up to become full blown codes if it occurs more than once) or Historic fault codes (would normally pop, but somehow remedied itself and wasn't cleared).