darnbro

I have a v220 ambiente 2000, with a auto gearbox started having a occasional problem when vehicle gets warm every now and then the box stays in low gear then eventually it changes with a thump, if I pull lever back to 3 instead of drive it changes immediately ok the box is a ZF 4HP20, anybody got any ideas or is the box on its way out?

CDM Motorsports

zf's are pretty reliable and simple working transmissions.
Have you checked basics? Fluid level and condition any codes?