I bought a cheap Hantek 6022BE to learn with and I'm just trying to measure some voltage to check if it's accurate. I'm using openhantek6022 https://github.com/OpenHantek/OpenHantek6022 and also hscope on android. I'm measuring a 19v laptop power supply with the 10x setting on the probe and also a set of leads with a 20x attenuator. When I measure the power supply with my dmm I'm getting 19.22V with the scope I'm getting much higher or lower depending on where I set the voltage per division. Both programs have a calibration function which I did.
20x attenuator showing 19.6v
10x probe showing 20v
10x probe with 2v per division setting only showing 9.81V
Hscope showing 19.9v
I wish you the best of luck in your automotive endeavors. But specific to that field, be advised that automobile power can have a lot of voltage spikes, most notably right after the starter motor shuts off after ignition. This could be as high at 15v or around there. So if you're not probing during this dynamic event, then your scope will likely still be useful.
I will also note that a used benchtop scope can be had for about $200 USD, often with good tactile controls and acceptable bandwidth and voltage capabilities. A cursory search on eBay shows a 2-channel 50 MHz Siglent SDS1052DL with 400 volt inputs. For general technician and hobbyist diagnostics work, that's a good deal for an instrument that is one step above what a competent DMM can provide.