Tape guides first. The other thing is when changing or examining the tape guides, clear off any accumulated metallic dust on the stationary magnets and sensors. The car picks up small magnetic particles on the two magnetic slugs that work in tandem with the DPP1,2 sensors as it runs over time. They form little piles which move. So your signals might work for awhile then stop, then work again. The other thing is often overlooked. Those modules degrade with time, like anything using optoelectronic technology.
