Emission light stays on

The Engine Computer detected a problem, set a diagnostic fault code, and since the problem could have an adverse effect on emissions, it turned on the Check Engine light. It's important to understand that codes never say to replace parts. While the part referenced might actually be defective, about half of the time there are other causes.

Here is a guide that will help you get the codes

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Another important point related to waiting to have the repairs done is the Engine Computer is constantly comparing different sensors and operating conditions to determine when there is a problem. When a problem has been detected and a code has been set, the computer knows it can't use that as a reference for other self-tests, so it won't run them while you're driving.

A totally different new problem could develop causing poor performance, excessive fuel consumption and an overheated catalytic converter, or increased emissions, but no additional codes will be set, . . . that is until you have the first problem fixed. The mechanic can only provide an estimate to repair what he knows is needed. Based on the code(s) currently in memory, he knows which circuits to diagnose. He can provide a more accurate repair estimate once he finds the cause of the problem.

Once those repairs are completed the other self-tests can resume, typically hours or days after you get the car back. THAT'S when the new code(s) will set. You assume you paid for the wrong or unneeded repairs, but in reality you're just getting the first indication that the computer knows about the totally new and different problem. That is much less likely to occur when you have the first problem fixed right away.

As far as being dangerous, typically not as far driving in a safe manner, but some problems can become very expensive very quickly if they are ignored. Many problems only affect emissions and not anything that relates to engine wear or will lead to a breakdown. The place to start is by having the codes read, then we can make an educated decision on whether you want to ignore the warning.

Please run some tests and get back to us so we can continue helping you.

Best, Ken