OBDii–Use before & after you buy a vehicle?

[Nomadic1]

OK aside from my newcomer post, here’s my first official post.  Admin can please move it if it belongs somewhere else, but while the object of the discussion is not new, motives for it’s use are in fact varied.  This is a long post and I apologize, but I cover what I think are at least couple of particular issues for those in search of a dependable used vehicle.
 
I plan to move back to the States in Feb.2019; gotta buy a vehicle of course.  While I fully intend to have prospective vehicles inspected before buying, THAT can get seriously expensive!  I thought buying a good OBDii device and plugging it in during the test drive can’t hurt.  If it flags something potentially serious, I can weigh whether or not it’s worth paying a mechanic to look deeper or not.  The dealer might even own up about the known problem once the cat is outta the bag?!  Won't hold my breath! Now I researched and know the cheap OBDii’s around $35 are just crappy Chinese knockoffs of more serious models and are to be avoided at all costs.  In fact, reading some OBDii related posts here, re-enforced what I read that seemingly they can CAUSE problems by malfunctioning and resetting things that ought not to be reset!
OK, so I bought “BlueDriver” (no affiliation-just my research that indicated this was best for what I needed).  It’s an OBDii device designed and supported by mechanics. It has a free Bluetooth app that not only tells you the codes (et al), it shows you the possible problems linked to those codes and the most common solutions mechanics used to resolve those issues in your particular vehicle, in plain English.  And they update the firmware with new capabilities.  Sorry if it sounds like an ad (again no affiliation), I simply was sold upon doing my research, your mileage may vary.    Yes, those OBDii’s that have fixed displays are interesting, but depending on where you park, you might be asking for a break-in?  Not to mention those displays are made to be installed and carrying all that hardware into a used car dealerships vehicle versus a simple plug, might well (justifiably?) cause a dealer to say ‘not in my cars’!?
Yes, there be questions here!
Anyone used a good OBDii device before buying a used vehicle from a dealer?  And before taking it to a mechanic for a thorough checkup? How’d you make out?  Did the dealer balk?  Did you have a mechanic check it anyway only to find some problem the OBDii would’ve flagged?
I would/will likely walk away from the dealer if the latter happens to me.  I mean they’re diagnostic devices, as such they should do no harm (apart from aforementioned poorly designed cheapo knockoffs).  Or OBDII's something used car dealerships just ban outright?  I’ll still be glad I bought it for later use! Thanks in advance!

 

[highdesertranger]

it's really not going to show anything major unless the check engine light is on. readers can be good and they can be bad. you must know what you are doing to get the full benefit of them and in the wrong hands can do more harm than good. highdesertranger

 

[tx2sturgis]

I think it's probably a good idea in theory, but although the OBDII port connections are (more or less) standardized, the data atreams into and out of the port are not.

There are some common connection protocols, but the various manufacturers have implemented some odd-ball 'handshakes' between their vehicles and the diagnostic software they use.

You could try it, but there is no guarantee that if there is an issue with say, an emission device, or a transmission temperature sensor, or a diagnostic code, that your reader will even see it, much less be able to display it.

Depending on the reader, it might or might not have all of the correct signaling protocols for the vehicle you plug it into.

I have only used two of them, on two different vehicles, and some programming was involved to 'help' each unit work with the vehicle it was plugged into. 

Some basic info:

https://scantoolcenter.com/obd2-basic/which-obd-2-protocol-is-supported-by-your-vehicle/

http://www.obdii.com/connector.html

 

[bullfrog]

Most really good mechanics can notice a problem before the check engine light comes on and will use the tester to verify what they already know. I would think you would be able to avoid some vehicles with really bad problems but you may pass on some really good vehicles with really small problems that could be easly fixed. A really good mechanic is worth paying for when spending big bucks on a vehicle.

 

[Manyways2go]

As simple as I can:
Generally diagnostic scanner OBDll used after 1996 works best to gather information to be used when a problem already exists.
When yellow check engine or Service engine soon dash light is on there is a code stored called a hard code which you could read
and research, or erase code(s) to see how soon it comes back.Electrical systems,sensors and actuators can be very complicated
even with experts complicated by vehicle types and models using different part numbers.

If you just wanted to learn or just become more familiar with your vehicle it works well. To solve problem
it may direct you to a system to check for detailed testing, other than that it would be guessing and feeding parts with fingers crossed.
If you are bit technical it helps but you could always research these days online, fairly simple tool and I don't expect you would be able to
make any damage.  A lot are inexpensive enough that I sometimes buy an extra to give away.
I hope useful info for you or forum members

 

[johnny b]

I bought one of these as an easy way to add a tachometer....plus it is a code scanner along with trip computer.
As mentioned, reading codes is only the first step after the 'check engine light' comes on.

https://www.scangauge.com/

 

[B and C]

Yep. I have one of those mounted to my steering column right behind the steering wheel. I keep it on the MPG setting and RPM setting mostly. I will change MPG to trans temp if climbing a mountain. It is nice to have the tachometer when descending so I don't over-rev the motor. Most of the time I descend in third and apply brakes briefly to slow down. If applying brakes too often, I will slow down more and drop into second.

 

[Nomadic1]

OK, thanks again everyone for your input.  As I said in my opening post, I will definitely have a mechanic check any vehicle before deciding to purchase.  I've since read a bit more and generally it is recommended to bring your OBDii device when used car shopping.  While some say it is not useful unless there is a check engine light on, others insist if something is off (real time data) but not to the degree it has tripped a warning light just yet, then one might have a heads up to a problem.  Also, some dishonest used car salesmen (oh no, that's like sayin somethin' bad about lawyers.. LOL) could have easily turned off (and regularly turned it off repeatedly to hide a problem) a warning light with an OBDii.  Yes of course, when a mechanic checks it during pre-buy inspection it would turn up... but then you've wasted money on an inspection when simply plugging an a scanner 1st could've warned you.  At least one person wrote he wished he'd had it as a light came on as he drove it 8 hours to his mechanic to have it inspected.  He bought it up front, presumably due to the distance to his mechanic.  For me, I'll have to pick a mechanic in the area and hope he's decent, it's like trying to find a good GP in a new town... shooting in the dark, but any inspection by a mechanic is better than none before buying and my point is checking it with an OBDii during the test drive just may save you money you'd have otherwise wasted paying a mechanic to tell you a warning light came on during inspection!  As I also said, IMO these are good to have anyway once you own a car, I felt and feel my pre-buy purchase of a device was sound.  Time will tell.  I'll try to remember to post what happened/happens when I begin my accelerated hunt for a used vehicle.  Since I'll be renting a car the 1st few days, I won't have the luxury of looking for weeks/months.  Other option is to buy a cheapo clunker and trade it in when I find my car, but that could literally and figuratively back-fire if it breaks down. Then I've got to rent a car anyway, pay to get the clunker functional again and hope I can trade it back in!
Thanks again everyone who chimed in!  I do appreciate the feedback.