I bought a cheap (sub $10) ELM 327 Bluetooth clone OBD-2 diagnostic adapter on a local "ebay-style" market where the seller specializes in car diagnostics and has several thousand positive reviews (read: I guess this seller would not provide anything really harmful). The adapter is labeled with an "ELM327 v1.4" sticker and the device identifies itself as an "ELM 327 v1.5" over serial. I know v1.5 does not officially exist in the original ELM.

The adapter was able to pair with a European 2006 Volvo XC90. I ran through a few free diagnostic apps (namely 5 of them: Torque free, OBD Car Doctor free, DashCommand, ScanMaster and OBD Auto Doctor) while some of the apps connected to the car successfully to show OBD info, some could not connect. I was using the diagnostics for about 30 minutes.

A few hours later, the car had problems with starting the engine - a kind of "engine error" light flashed on the dashboard, but the car computer (the text display) did not display any problem. The car did not start on the first attempt but it did on the fourth. There was also low fuel in the tank which could have caused the bad start but probably not the "engine error" light (this light then disappeared).

My question is simple - can there be harm caused to any car or its electronics in general by using the OBD-2 diagnostic port? I know one can also write messages to the CAN bus with it but I have no idea what consequences some bad writes can have.

The photo of the adapter:

Photo of Bluetooth adapter


I am asking on 2 levels:

  1. Can harm be done via OBD in general (with any equipment/scanner etc.)?

  2. Can harm be done with the ELM 327 clone device I used?


The reason for engine starting problems was low fuel. More fuel was tanked and now the car starts without problems again.

  • Were there any error codes to begin with? Did you clear some error codes with the tool?
    – Zaid
    Commented Aug 5, 2015 at 10:48
  • One of the apps showed a list of error codes and it was blank - so no, there were no errors logged in OBD, the car was supposed to have no problem.
    – Kozuch
    Commented Aug 5, 2015 at 10:50
  • Another question: How long were you testing apps for, and was the engine running during this time?
    – Zaid
    Commented Aug 5, 2015 at 10:52
  • The car was driven about 300 km that day before and then I made the diagnostics with the engine off, the key in ignition was in position "II" (=2, the last position before engine starts). I tried first with ignition totally off (key out) I guess, then position 1 and finally pos. 2, because those previous did not work properly. It was my fist time doing car diagnostics and I am not a mechanic by job. PS. I was in the car for about 30 minutes.
    – Kozuch
    Commented Aug 5, 2015 at 10:56
  • New beetle 2000, I put a 327 obd2 elm and I used it for a few months to see the speed, tachometer and engine warm up, now I have serious suspicions that it has ruined the engine time, it has a uneven idle. The computer does not give error codes. Commented Jun 21, 2017 at 16:36

12 Answers 12


It is highly probable that the reason your car was reluctant to start was that the time you were running diagnostics had sapped some of the charge from the battery. The battery on the car will not charge unless the engine is running.

It is unlikely that this device would harm your vehicle but it is theoretically (and practically) possible to do temporary or permanent damage; here are some examples.

With certain generic OBD-II port reader dongles plugged into the diagnostic port of the Ferrari 430, the Traction Control System goes offline. This was noticed at a track day by an owner who was using a bluetooth OBD-II dongle for logging.

On the Volkswagen Immo3 security system, new keys are added using a piece of software called Vagtacho. This software uses the OBD-II interface to connect to the instrument cluster and add new transponder codes. This software also allows features such as illuminated dials to be enabled. It works be reading the complete e-prom of the cluster and allows users to poke new values into this data extract then upload it over the top of the existing e-prom. It is possible to do real damage to a car if you get this wrong.

So, in theory, if one of the applications you used with this device tried to perform an unsupported operation which the car misunderstood, you could damage the car. However, this is incredibly unlikely to happen given the activities you have described.

  • Could you please provide a source for the Ferrari 430 traction control story?
    – David Lord
    Commented Aug 6, 2015 at 0:41
  • Here is another example where simply setting the wrong baud rate caused (non permanent in this instance) ABS problems priuschat.com/threads/…
    – JamesRyan
    Commented Aug 6, 2015 at 10:56
  • 2
    @DavidLord yes; me, I saw it with my own eyes. Thankfully it was spotted before the car went out on the track. It seemed to put it into some kind of safe / limp mode. Very worrying as I was working for a specialist insurer at the time and was investigating OBD-II "black boxes". This was just a cheapy bluetooth data connector with a phone based app but the car wasn't having any of it. Could well have been classic Italian electrics though. Commented Aug 6, 2015 at 11:19
  • See also, e.g. Car Hacking – With Bluetooth OBD ← Terence Eden's Blog
    – nealmcb
    Commented Jun 2, 2016 at 16:59
  • Another small data point: my cheap OBD2->Bluetooth adapter sometimes causes the Traction Control warning to intermittently alert on my 2008 Chevy Impala. I haven't dug too deeply into it, but I suspect it has something to do with the dongle overloading the CAN bus, and traction control getting unhappy that it's not receiving its data when it expects to.
    – maples
    Commented Jan 27, 2023 at 19:37

To my knowledge there is no way a scanner can cause issues with your computer electronics. This device is a read only device. It doesn't change anything in your computer. It does, however, communicate with the computer. Through this communication it can give the computer commands, such as to clear the codes. This doesn't write anything to the computer, but rather instructs the computer what to do.

I think your issue lies with the gas at the bottom of the tank vs. the new scanner.

EDIT: Because you updated your question, I'll update my answer:

  1. Can harm be done via OBD in general (with any equipment/scanner etc.)?

Absolutely. If you hook a welder up and juice the PCM through the OBD with a gagillion amps, you will fry the electronics of the PCM through the OBD port. (NOTE: Would you do this? Probably not on purpose, but it is possible.) If you use a tool to remap the fuel curves within the PCM and pull the cable before the entire remap is written, you will cause damage to the PCM. There are probably a million (on the conservative side) different ways you could possibly damage your PCM or anything on the CAN Bus electronically through the OBD port. The probability of it happening depends on what you are doing and how you are doing it.

  1. Can harm be done with the ELM 327 clone device I used?

It could possibly cause harm, but the probability of this happening is remote. I'm sure there are about a 100,000 of these devices being used out there, by whatever manufacturer. It is meant as a read-only (meaning, it will communicate with the PCM and read parameters) device, not as a device used to reprogram the PCM or other components which ride on the CAN Bus. Could someone utilize this device in such a manner? Yes, no doubt. If you are using the device as prescribed, you have not done any tampering, and you are utilizing the device programming as provided, the chances of anything happening to your PCM or other electronic devices on the CAN Bus are extremely remote. When I say extremely remote I mean the chances are just above nil. If it were to electronically short circuit, anything is possible.



The tool in and of itself cannot do any "harm" to the vehicle.

If you were testing apps with the engine off, it is quite possible that the battery may have drained to the extent that it gave some hiccups while starting. Low fuel level may also be to blame here.


If the vehicle has error codes present which are cleared with the tool, the vehicle's behavior can change and bring up symptoms that were not experienced before.

Note that this is not the fault of the scanner since the person operating the tool has to make a call. The scanner is simply the means to achieve it.

  • 3
    @JamesRyan : I never said it was read-only. Did you read the second half of the answer?
    – Zaid
    Commented Aug 5, 2015 at 11:42
  • 1
    @JamesRyan : Let me repeat this one more time: the scanner is not a read-only device; I don't know where you see that in my as-of-yet unchanged answer. It can receive signals (read codes) and send signals (clear codes). Playing the "Made in China" card doesn't change the fact that you misread this answer. In fact, judging by your comments I wonder if you even read the question - you can't just read the title of the question and ignore the rest of the question body!
    – Zaid
    Commented Aug 5, 2015 at 13:16
  • 4
    The dongle doesn't do anything special in and of itself. It is merely a bluetooth serial port for your car. If something nasty happened via OBD2, it was more likely caused by one of the apps. Though I've been using Torque for years and I've never had a problem. Commented Aug 5, 2015 at 13:31
  • 6
    @JamesRyan This is not productive conversation because you are not providing evidence for what you are asserting. You also claimed Zaid's answer is wrong because "the interface is not read only !". Re-read his answer. He did not make that assertion. Commented Aug 5, 2015 at 14:35
  • 1
    @DavidWinslow re-read my comment. The ODB port allows a device to do damage because it is not read only. There is no sense checking against incorrect input from the device or operator. You have absolutely no indication that this device is compatible, reliable, trustworthy and yet he is stating (and you seem to agree) that it couldn't have caused damage when in fact it is entirely possible!
    – JamesRyan
    Commented Aug 5, 2015 at 14:41

Just this morning I connected an ELM327 to a '05 Volvo XC90. After only 1km, the message was displayed for "Anti-skid service required", and then "Anti-skid temporarily unavailable". I removed the ELM, and went home, and checked the car on the laptop based Volvo VIDA/DICE. This showed a BCM fault, CAN network communication error with SAS (steering angle sensor). It had only a single error count. The car has no history of this fault, and it has not reoccurred after I cleared it this morning. It seems to me that the ELM327 can possibly cause CAN based faults, as it seems happened in the Ferrari example above.


I recently purchased a 'ebay' obd2 dongle. Plugged it into my 06 Mercury mountaineer, to check a CEL code. I was using the Torque app. Drove with it for a few miles and the Wrench symbol came up on my display. Truck went into a limp mode. I turned the truck off, removed the dongle and returned home. Next day used the truck and it was fine. Jump forward a few days later. I plug the dongle into my wife's 04 toyota rav4. Get some real time data, but then notice the VSC and ABS lights are lite up on the dash. Turn the car off, turn it back on and now it has a rough idle and actually shuts off if I don't give it gas. Remove dongle and car returns to normal. Jump forward 2 weeks, today. Plug dongle into mountaineer to read a CEL, bad O2 sensor. Got distracted and leave dongle in. Wife goes out in mountaineer, calls me saying the truck is acting weird and the wrench symbol is on. I told her to shut truck off remove dongle and she'll be fine.

So I do believe the cheap ebay obd2 dongles do do something to the ecu's.


I just had a problem using one of this OBD2 Bluethoot module on my Chevrolet Trax 2015, where my Traction Control System stop working (Engine and TCS dash lights came on), also the transmission wasn't able to shift gears. I even have to push the car back to the parking spot. No air conditioner, no MPH reading, no fuel efficiency info. Unplugged the OBD2 Bluethoot module but no luck. Waited a few hours and everything went back to normal. Dumped the OBD2 Bluethoot module and deleted the app.


I am writing an OBDII app for Android and my extensive testing has showed that Yes it can have a negative impact on the cars performance. I have had test outcomes where all the lights on the dash light up and the engines torque is reduced. I believe this could be related to overloading of the OBD circuitry with constant commands being issued from an app. I'm sure that most/all current OBDII apps out there have undergone extensive testing for this and I would recommend that you do not expose your cars multi thousand dollar circuitry to a $10 adapter that is driven by a $2 app. Maybe look for guarantees and/or evidence of extensive live testing. Most of these apps are written with OBD simulators, which of course will not show any engine/circuitry degradation.

  • Overloading the OBD circuitry? Sounds like something from a bad sci-fi movie. The OBD circuitry is the ECU uC responding to commands. If the dash lights lit up or the torque was reduced then it's a valid response from the ECU. What did you send? Commented Jul 13, 2016 at 10:50
  • The CAN bus can be either 250 kbit/sec or 500 kbit/sec. The bandwidth is shared amongst many devices, including your speedo, tach, all your dash displays, ABS computer, etc, etc. The layout for every car is different so the total number of devices on the bus varies, but it's not hard to imagine cars with a lot of traffic on a common leg of CAN. The overload is not electrical, it's an overload of the available data transfer on the bus. Consuming half the available bandwidth with requests, starves the vehicles systems. Supposed to be a priority system that prevents this but... Could happen..
    – cdunn
    Commented Mar 29, 2017 at 21:37

I just tried a cheap Konnwei adapter on my electrical C-zero - It creates lots of havoc, warning lights ect come on, car wont start -

Fortunately after a restart with adapter removed every thing is normal -


my car was working fine, until I decide to plug in my obd reader while driving on the motorway, where it came to a near complete stop, I plugged it out quickly and took off again, everything seemed fine until I got off the motorway, and was driving in limp mode, I stopped the car and tried reset the ecu, to no avail, so I went to the nearest motor exit with a down ramp and built up a enough speed to get somewhat home, after stopping on the motorway, my car was reving in gear but no movement, until I stuck the obd sensor in and now its back in limp mode and moving.


Xc90, 2008. I was driving and using Torque app and plugin to make a chart for boost/rpm. For 5 km everything was OK. Then i stopped, switched the ignition off and checked my tire pressure for maybe 2 minutes. The car started OK, moved maybe 2-3 meters and then i felt something like kicking or like one tire slipped on the asphalt. Then Antiskid system errors + automatic gearbox switched to limp mode (showing "-" instead of "D"). Ignition off, chinese elm327 out of the OBD, ignition on - everything was OK. Then i checked with VIDA for errors: BCM-0115 Communication between control units communication problems with SAS signal missing BCM-0148 Communication between control units Wrong configuration ID TCM-e000 Control module communication Faulty communication

For me, this is the chinese elm327 screwing wit the bus of the car, disrupting the communication between the modules. More thesting will be done when i manage to put new OBD connector in my trunk.


Of course you can damage a car by plugging in a something into the OBD2 port. You're attaching an electronics device to an electronics port. Broken devices can create all sorts of problems, shorts being just one of them.

Is it likely? No. Possible? Yes.


I just got back from a Kia dealer as I was having a variety of electrical issues with my 2011 Kia Sedona (160000 km). I have a vGate OBD-2 bluetooth adapter and run Torque Pro on my 7" android head unit. The MIL lights that were coming on were as follows: battery and brake light and a corresponding drop in voltage measured by Torque Pro. Then, if the voltage dropped enough, the head unit would power down and restart. A few days later, the ABS, ESC and engine light came on. My speedometer needle started bouncing wildly. At this point, Torque pro started displaying erroneous data for such things as my oil temp, transmission temp and many other sensors. I disconnected the battery for 10 - 15 minutes to clear codes and reset but didn't think to remove the adapter. After a reconnect and restart, all the same MILs reappeared. In short, all errors returned. The Kia tech said that leaving the adapter in for extended periods of time can cause these errors. Removed the adapter and reset the ECU and everything is back to normal. I did a 40 minute drive and no MIL lights returned. So, I believe that leaving the adapters in can cause, minimally, temporary issues. The Kia tech said it's not an issue to use the adapter, but it's good practice to take in out when not in use.

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