There are high flow by less substrate material and high flow by good design. Ceramic and metal. You can get good aftermarket ones for less than stock ones. I would buy some and take it to a shop to install instead of buying whatever the shop is selling.

As for codes...if the tailpipe is emmiting clean air but the cell is lighting, you can get a spacer that places the probe a little further out and that USUALLY prevents the cell.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods