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. So, all damaged products are considered damaged during the transit, even though the outer boxes are not damaged. Professional installation will be HIGHLY recommended. Skilled technicians who have the proper tools and training should correctly and safely add the equipment to your vehicle. Buyers will be responsible for all risks on any installation method. We won’t accept any claim after 14 days upon item receive. What customers should do is to make sure the item is in the original packaging with the order number issued by our company Xpert-Tuning, clearly marked outside the box. We are committed to providing you with high-quality products and professional after-sales service. 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.