# Would you allow a prospective buyer of your second hand car to insert an odb2 scanner? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [May 25, 2022, 3:20pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084 "2022-05-25T15:20:51Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Saffer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saffer/32/6440_2.png) [@Saffer](https://boards.straightdope.com/u/Saffer)\ **Post date:** [May 25, 2022, 3:20pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/1 "2022-05-25T15:20:52Z")
An odb2 scanner is a standard tool that connects to a little port under your dashboard somewhere. It tells the user various details from the car computer, including any error codes or warnings. Is this a legitimate tool for a cautious buyer to employ or can it be used (accidentally or maliciously) to harm the car? ---
**Author:** ![dolphinboy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dolphinboy/32/330_2.png) [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)\ **Post date:** [May 25, 2022, 3:23pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/2 "2022-05-25T15:23:49Z")
I don’t think it can usually be used to harm the car, but I suppose it could insert a virus that causes problems, but why would someone want to screw around with your car’s software? I think they are likely just looking to see if you abused the vehicle, for example revving the engine, driving excessively at high speed, etc. Is that a legitimate thing for a prospective buyer to do, I think that’s up to you. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [May 25, 2022, 3:24pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/3 "2022-05-25T15:24:02Z")
> [@Saffer](#): > > Is this a legitimate tool for a cautious buyer to employ It’s a legitimate tool for _any_ buyer to employ. ---
**Author:** ![Saffer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saffer/32/6440_2.png) [@Saffer](https://boards.straightdope.com/u/Saffer)\ **Post date:** [May 25, 2022, 3:27pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/4 "2022-05-25T15:27:04Z")
Ok great, because I have acquired one for exactly this purpose. Just want to make sure I am on the side of sense if anyone refuses to let me use it on the grounds I could damage their car. I have not yet used one though. ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [May 25, 2022, 3:29pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/5 "2022-05-25T15:29:34Z")
The ones I’ve seen can damage a car if not run through the proper sequence. While they are simple to use I can see someone not letting someone unfamiliar with the tool letting them practice on their car. Myself I have one on my car, so I would run the diagnostics for them. > **[OBD2 Scanners: Do’s and Don’ts of Using OBD2 Scanners](https://www.totalcardiagnostics.com/learn/obd2-scanners-dos-donts-using-obd2-scanners/)** > > Cars have become nothing short of computers on four wheels. The on board diagnostics or simply OBD2, introduced in car models as from 1996, has made it a necessity for every car owner to learn about car diagnostic tools. OBD2 scanners are one of the... ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [May 25, 2022, 3:49pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/6 "2022-05-25T15:49:04Z")
Many potential buyers like to take the car to their mechanic to inspect. I assume the first thing they would do would be to run a scan. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 25, 2022, 3:53pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/7 "2022-05-25T15:53:02Z")
I’d let someone do it. I don’t hustle used cars, all I want is a fair price. I would have already scanned it and would be interested if a different scanner turns up something new, but it’s unlikely to make me lower the price, it will already be priced to move. ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [May 25, 2022, 3:54pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/8 "2022-05-25T15:54:54Z")
There is a difference between a professional mechanic running a diagnostic tool and my inept nephew. If anyone balks at having a mechanic look at the car run the other way. Also, a seller can use a OBD2 scanner to reset a code and hide it from the buyer. I’ve heard of people that had issues with an O2 sensor causing a light on the dash to come on. Resetting the code turns off the dash light, which can come back after a time of driving the car. Time that a buyer may not have. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 25, 2022, 4:21pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/9 "2022-05-25T16:21:19Z")
> [@Si\_Amigo](#): > > Also, a seller can use a OBD2 scanner to reset a code and hide it from the buyer. I’ve heard of people that had issues with an O2 sensor causing a light on the dash to come on. Resetting the code turns off the dash light, which can come back after a time of driving the car. Yes, so then allowing a prospective buyer to use a scanner will be dependent on the seller knowing what codes the scanner would report already, and being able to watch and understand what the buyer is doing with the scanner. And if you are a buyer you should know there are codes that could have been reset and will show up again. A good reason to take a car you want to buy to a mechanic. They can’t tell you everything either, but you always take that risk buying a used car, there could be problems even an honest owner didn’t know about. And anything could break tomorrow when it’s your car. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [May 25, 2022, 4:30pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/10 "2022-05-25T16:30:33Z")
> [@Si\_Amigo](#): > > Also, a seller can use a OBD2 scanner to reset a code and hide it from the buyer. I’ve heard of people that had issues with an O2 sensor causing a light on the dash to come on. Resetting the code turns off the dash light, which can come back after a time of driving the car. Time that a buyer may not have. Yes, the person selling the car may have already used a scanner to delete any stored codes so when you as a prospective buyer plug your scanner in to check you will not find any codes stored. That doesn’t mean everything is good with the car. It takes a certain number of cycles of various sensors for the computer in the car to reset the codes after they have been cleared. In areas where your car has to undergo periodic testing to renew your registration their tools can usually tell if the codes have been recently cleared and will return a not ready signal and you may not pass inspection. I am not sure if your little handheld OBD II scanner will tell you that. ---
**Author:** ![Saffer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saffer/32/6440_2.png) [@Saffer](https://boards.straightdope.com/u/Saffer)\ **Post date:** [May 25, 2022, 4:37pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/11 "2022-05-25T16:37:46Z")
> [@Dallas\_Jones](#): > > I am not sure if your little handheld OBD II scanner will tell you that. Actually I have purchased the cheapest one I could find. In USD equivalent it is less than $10. Since I have never used it, it might even be an empty box that does nothing for all I know. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [May 25, 2022, 4:47pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/12 "2022-05-25T16:47:29Z")
When my CEL is on I go to the local AutoZone where they have a scanner free to borrow/use. ---
**Author:** ![SpacemanSpiff\_II](https://avatars.discourse-cdn.com/v4/letter/s/e19adc/32.png) [@SpacemanSpiff\_II](https://boards.straightdope.com/u/SpacemanSpiff_II)\ **Post date:** [May 25, 2022, 5:04pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/13 "2022-05-25T17:04:27Z")
> [@Dallas\_Jones](#): > > In areas where your car has to undergo periodic testing to renew your registration their tools can usually tell if the codes have been recently cleared and will return a not ready signal and you may not pass inspection. I am not sure if your little handheld OBD II scanner will tell you that. Typically, they will. Or at least the one I got - the cheapest one I could find - will do that. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 25, 2022, 6:34pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/14 "2022-05-25T18:34:56Z")
I have a fairly advanced OBD2 tool. With it and the associated PC software I can read codes, reset codes, and generally reprogram lots (i.e. hundreds) of little internal configuration options that affect how your car behaves. Baring software bugs in the car or my tool, I probably could not break your car with my tool, but I could certainly surprise you with the results if you let me play unmonitored with my tool on your car for a few minutes. So that’s one risk to the seller. On a modern computerized car, literally dozens of anomalies will be logged per driving day. Most are just noise. Only a small fraction, and maybe even none, are useful signal. A buyer who does not know the difference will be terrified when seeing a hundred problems in the log. A professional will recognize all but, say, one are utterly immaterial; they know that every car, or at least every car of that model, does that. Having a clueless buyer who can’t tell the wheat from the chaff may well scare that buyer away from your perfectly good car. That’s another risk to the seller. It’s also a risk to the buyer; the buyer may pass up a perfectly decent car based on ignorantly being afraid of chaff. Or may not find the legitimately scary wheat obscured amongst the blizzard of benign chaff. Finally, if the seller has an OBD2 tool, they can clear the history before the buyer sees it. But the fact the history is clear, or only goes back e.g. 3 days, will be obvious to a skilled buyer with his own OBD2 tool. As a skilled buyer I’d be far more concerned about a clean 3-day or even 30-day history than I would be about a messy multi-year history. Like a tampered odometer, the former only tells me I can’t trust anything I (don’t) see. The latter isn’t proof it’s 100% the unvarnished truth, but it’s highly suggestive of truth. _Caveat emptor. Caveat vendor._ ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [May 25, 2022, 6:41pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/15 "2022-05-25T18:41:37Z")
> [@Dallas\_Jones](#): > > In areas where your car has to undergo periodic testing to renew your registration their tools can usually tell if the codes have been recently cleared and will return a not ready signal and you may not pass inspection. This almost happened to me. I had a very intermittent sensor problem that would cause the light to turn on every couple months, then go away on it’s own a day or two later. I borrowed a OBD2 scanner and found contradictory error messages - something-something too rich as well as too lean. The car ran fine so I ignored it… till my registration was close to expiring and I had to pass the emission check. Sure enough, the light turned on a few days before I was due. I cleared the codes and had to perform a few dufferent types of driving. I forget the specifics but it was a certain number of starts, some miles above (say) 60 mph, some miles above 30 mph, that sort of thing. I passed the test! It wound up being the positive crankcase ventilation (PCV) valve. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [May 25, 2022, 6:42pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/16 "2022-05-25T18:42:15Z")
> [@LSLGuy](#): > > I have a fairly advanced OBD2 tool. With it and the associated PC software I can read codes, reset codes, and generally reprogram lots (i.e. hundreds) of little internal configuration options that affect how your car behaves HP Tuners? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 25, 2022, 6:45pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/17 "2022-05-25T18:45:18Z")
Carly. Es für Deutsches autos. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 25, 2022, 7:51pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/18 "2022-05-25T19:51:22Z")
> [@jnglmassiv](#): > > r. I borrowed a OBD2 scanner and found contradictory error messages - something-something too rich as well as too lean. Common type of things. Fuel sensors may be working against each other. The codes are just the start of the diagnostic process, and unfortunately you may end up having to replace multiple components to make it go away, and if the make of your car starts with V just plan on taking it to the dealership. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 25, 2022, 7:52pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/19 "2022-05-25T19:52:05Z")
When I was used car shopping, every car I considered I plugged my scanner into. I was particularly interested in seeing if it was recently reset (erased) and also if it was ready (in a passing state) for NY inspection. I never got any pushback and really I could not consider the car if I were prevented from doing so by the seller. I also did find a fair number of cars that were recently reset and not in a ready state. Some scanners will show the hours from the last reset, others/all will show if the car is ‘ready’, either way (not ready or the hours) can indicate a recent reset. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [May 25, 2022, 8:10pm UTC](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084/20 "2022-05-25T20:10:11Z")
I didn’t answer the OP. Sure, I’d let a buyer plug in. > [@TriPolar](#): > > … you may end up having to replace multiple components to make it go away … Yes, I got lucky and got the right part replaced first try. After the scramble to pass emissions, I did my research and narrowed the codes down to a few possible problems, most having to do with oxygen sensors. The PCV valve was the easiest for me to replace as it’s on top of the engine and was pretty inexpensive as well so I started there. [Next page](https://boards.straightdope.com/t/would-you-allow-a-prospective-buyer-of-your-second-hand-car-to-insert-an-odb2-scanner/965084.md?page=2)