some warning lights on

Hi Guys,

I have Pontiac Sunfire 2000.

After head gasket changed on my engine two warning lights on instrument panel came up – “Check engine” and “Enhanced Traction System”.

Mechanic figured out it could be a sensor and changed it to a new one. But, after a while of driving those lights came up again.

In a one thread (on this forum) I’ve read it could be faulty ground wires that could be the ones under or by battery hold rack but that thread wasn’t finished to put more light on it.

Could anybody advise anything on this problem?

Thanks