As I reply to similar questions, it is simply impossible to provide definitive answers to the sort of questions you pose. However, I'll give you my views (which you will appreciate is not quite the same thing).
The CPS must decide if the actions your friend is alleged to have taken were committed deliberately or recklessly (as to the consequences). If neither then no offence is likely to be charged with the possible exception of careless or dangerous driving (and careless is the more likely). If they believe that his actions were taken deliberately to harm the victim or recklessly as to the consequences then ABH or GBH is a possibility (a vehicle being one of the most dangerous weapons available).
The choice of charge (Common Assault, ABH or GBH) depends on the level of injury. Common Assault is appropriate where little or no injury is caused. ABH involves serious injury. GBH really serious injury. As a taster, here’s the CPS guidance for GBH:
“Grievous bodily harm means really serious bodily harm. It is for the jury to decide whether the harm is really serious. However, examples of what would usually amount to really serious harm include:
• injury resulting in permanent disability, loss of sensory function or visible disfigurement;
• broken or displaced limbs or bones, including fractured skull, compound fractures, broken cheek bone, jaw, ribs, etc;
• injuries which cause substantial loss of blood, usually necessitating a transfusion or result in lengthy treatment or incapacity; “
So if the victim sustained a broken shoulder, GBH is a distinct possibility.
From your description the level of culpability does seem low. But the level of harm may be considered high and it may push the offence into Category 2.
However, your friend’s immediate concern is whether he will be charged and what with. When he next attends the police station he should take a solicitor with him.