* Broken or severely damaged reverse gear: A component within the transmission responsible for engaging reverse has failed. This could be a broken gear, a stripped shaft, or a problem with the reverse clutch pack.
* Transmission linkage or cable failure: Though less likely to cause *complete* loss of reverse, a broken linkage or cable could prevent the transmission from selecting reverse. However, if *all* other gears work, this is less probable.
* Internal transmission damage: More extensive internal damage, perhaps from low transmission fluid or a previous hard impact, could have affected multiple gears, including reverse.
* Hydraulic issues: Problems with the hydraulic system within the automatic transmission could prevent the reverse clutches from engaging.
You should NOT drive the vehicle in this condition. Continuing to drive it could cause further, potentially catastrophic, damage to the transmission. It will also be extremely unsafe.
You need to have the vehicle towed to a qualified transmission mechanic or repair shop. They can diagnose the precise problem and provide an accurate estimate for repair or replacement. Expect a significant repair bill, possibly exceeding the value of the vehicle depending on its overall condition and the extent of the damage.
