OBD2 Reader?
 

So here is something I understand but am confused at the same time.


OBD2 scanners. I have a cheap-o from who knows where. I does read codes. Except when it doesn't. Sometimes you need to go to a legit mechanic to get the codes read because my poor scanner doesn't pick them up.

In my very simple brain I think that a digital signal is a signal is a signal. And a reader should be able to extract it.

Can anyone explain how a cheap reader can in fact read codes but at the same time not pick up other codes?

Thanks all!

Some codes are proprietary to a vehicle.
(ie there are 5 computers involved in opening a sunroof on a particular model)

OBD2 is supposed to 'universal' to basic function...from 1995(Canada) or 1996(USA) i think...but things have changed.

Depends on the brand. I have brand specific readers for my Audi, BMW and Porsche and they work great. If you can find one specifically for your marque instead of a generic one, you are golden. Just remember to update software.

Depends on what modules it'll read as I understand it. There are a lot of generic emissions codes that virtually all readers will read but those same readers won't read all the modules. I have a Blue Driver that I'm satisfied with. I haven't had to take any of my older vehicles in to have codes read. If you want more codes it seems like you have to step up in price to a "diagnostic" scanner. Those let you do things like cycle the ABS when bleeding brakes and see transmission codes.

There's a reason some scanners are $20, and some are $1,500. You get access to vehicle specific codes, data streaming, and freeze frame data. My Volvo rarely shows 'check-engine', but if I scab it with Volvo's VIDA software, I will see at least ten faults/warnings.

Watch any legit mechanic on YouTube and you will only see the high-end scanners.

My $20 scanner has been reading "check engine" codes for me for years on multiple cars.
It's all I have ever needed.

Proprietary. That is a great answer. Makes sense. Thanks!

Fancy diagnostic scanners can actively send a lot of signals as well.

Cycle the abs solonoids for bleeding, operate the purge valves for emissions, cycle through electronic fan speeds to check operation, etc etc....

A good scanner will also plot your boost pressure, oxygen sensor voltages, abs signals, etc.

The cheap $20 scanners work for cheap $20 fixes. Heck any auto-parts store will scan for free in their parking lot..........but for ABS, and higher end problems, the $200+ scanners will clear codes the cheapo's won't.

My $100 Blue Driver will clear about anything and has real time logging.

I think the deal is that back when OBDII was created, (in the 90s) the amount of computerized data was limited. These days there's a LOT more stuff in cars that's computerized, and manufacturers have added their own stuff. Think about the fact that there's now computerized suspension, transmissions, TPMS, multiple air bags, windows, etc... that were not computerized in the 90s. I suspect that instead of updating the OBDII standard to include all of these new things, the various manufacturers just added their own stuff. So now your scanner/diagnostic tool needs to support the proprietary codes for any manufacturers that you want to scan.