Open the electrical panel on the machine. I'm assuming this is a Soft Gloss. Step on the pressure pad closest to the exit (should be the one that is for back-up. Ensure input#25 comes on. Next block the the phot-eye at the rear of the wheel brush input #20 should go off. Next block the photo-eye on the exit side of wheel brush and input #12 should go off. Back-up pad should be about 15" from the entrance side photo-eye. It has to go off before the photo-eye detects the tire, if it does not this is why you are getting the code.