This unit will need to be coded with the installed diagnostic tool according to the. The prompt steps on the diagnostic instrument. If the original car has an error code, please use the diagnostic tool to. Eliminate it when installing the product. If the error code is cleared. After the elimination, it can be used normally. If the errcor code. The error code occurs because the switch of the trailer module is turned on. Please turn off the settings of the trailer module and it can be used. This product has a control module for trailers and tractors. Therefore, this product can be used for trailers and tractors. This unit must be programmed after installation. Please do not open the product without permission to avoid damaging the label. MERCEDES 164 900 54 01, A 164 900 54 01,1649005401, A1649005401. MERCEDES 164 900 51 01, A 164 900 51 01,1649005101, A1649005101. Will fit F ollowing M odels. Code 848: Electric windows. A correct address should be provided while placing your order. Most of our products do not come with instructions and won’t be provided, PROFESSIONAL INSTALLATION is highly recommended. Parts that are modified in any way or damaged as result of improper installation will not approved for return. During the high season time, there might be times that popular merchandise are backorder, we do try our best to keep the inventory accurate for the item that we list. There might be chances that the item is out of stock before we can stop the listings.