How to put an aftermarket exhaust on a car?

On my vw passat 2007 the orange exhaust warning light lit i left car to my mechanic who told me he put in a?

• new sensor anyhow the next day the light lit again and back i went to the mechanic who kept it another day and told me he had to put in 2 new heating plugs are these plugs related to the warning light coming on and where are the heating plugs ive now been charged twice this is the reason im asking i asked a the same question and everyone said the light was on because of the lambda sensor in the exhaust system also when the mechanic hooked the car up to a bosch diagnostic tool would this not have appeared at the start i only drove the car 6 or 7 miles after the first job when light came on again also are the heating plugs the same as glow plugs if so what is the connection to this warning light sorry if i sound suspicious but there are plenty of dodgy mechanics out there not all but some

• Answer:

  What engine?petrol or diesel? And what sensor was changed out first. The light is not an exhaust gas or lambda light,it's an engine malfunction light (EML). ANY faults in ANY sensor can trigger the EML to come on. Repairing any fault that'll trigger a stored code doesn't mean that another wont trigger it. Renewing a sensor can cause another to react. The lambda,or o2, sensor is the last in line,it's job is to monitor and adjust the fuel air mixture,but it can be damaged by a number of other sensor faults,and it sounds like your original faulty sensor was enough to do this.