I had an GREDDY EVO exhaust installed about two weeks ago,but ever since the install I've been getting a CEL.

At the same time the speedometer stopped working or it does work after a long drive,and the V-TEC either doesn't kick on or it kicks on for a couple of seconds, and the headlights and interior lights start to flicker like something is draining power,other than that everything is normal.

I ordered a DC JDM 4-1 Header and CAT to go with it, but i'm wondering if these problems will go away once the new stuff gets bolted on since a new O2 sensor will be used.

Before the exhaust install my R was running peace,now it's got me puzzled.

I've reset the computer numerous times,checked fuses,but nothing changes.

Is it just the O2 sensor or could it be something else?