Oxygen sensor and erg valve

The EGR valve lowers emissions and increases fuel mileage by partially filling the cylinders with inert exhaust gas rather than fresh air and fuel. A valve that's sticking open can cause stalling or rough running at idle when it isn't supposed to be open. It's more common for the black plastic disc on top of the valve to fail from moisture getting inside but at least up through the '99 model year you couldn't buy that part separately. You can find good used ones at the salvage yard. That's that part that will set a fault code. There are two oxygen sensors; one before the catalytic converter and one after. The first one is responsible for fine tuning the fuel / air mixture for the best fuel economy and lowest emissions. The second one monitors the efficiency of the converter to see if it's doing what it is supposed to. Besides the emissions and fuel mileage issues, when you continue driving with the light on, you will never know when a different problem crops up that can turn into something very expensive very quickly. Overheating and destroying the catalytic converter is the most common and expensive problem.

Two problems. The first is you should start a new question specific to your vehicle, and be sure to list the engine size and mileage. This was a private conversation between just two people, and as such, none of the other experts are going to see your addition or have a chance to reply. That may not get you the help you need, or as fast as possible. I'll try to help you here, but if necessary, copy and paste your post into a new question. Here's the link if you need it:

https://www.2carpros.com/questions/new

The bigger problem is the diagnostic fault code did not say to replace a part. They never do on any brand or model of car. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is actually the cause of that code about half of the time. Before we waste your money on a part, we have to rule out wiring and connector terminal problems, and mechanical problems associated with that part.

Here's the definition listed for this fault code:

"HO2S Heater Control Circuit High (Bank 1 Sensor 1)"

12 volts is typically fed to one side of the heater element, then the other side is pulled down to ground, or 0 volts. That ground side is the control side and that is where the problem is being detected. Those internal heater elements are really tough and rarely fail. That's why replacing the sensor isn't solving the problem. This is much more likely to be caused by a broken wire or corrosion in the connector. It is also not uncommon to find one of the terminals corroded right off inside the connector.