My friend has a 99 sh and he just got a Greddy Evo bat-back exhaust installed and the check engine light and ATTS light came on. Wonder if you guess know what is the problem. We scanned the car and it said the 02 sensor heater core is malfunction, but is the ATTS is suppose to be on?

 

the atts light comes on automatically aftre a CEL so its normal. what was the code #?

 

The ATTS light comes on when an ecu trouble code turns on the CEL.