Does OBD2 scanner consume the power when car turns off

Welcome to PriusChat! This is the perfect place to learn all you're ever likely to need to know about your Prius. I have a couple of ScanGauge IIs plugged into the OBD2 interface on my Prius, and they both power themselves off 30 secs ofter the 12V supply goes down (car switches off) - I've no idea if your scanner was designed to do the same thing (it would be if I had designed it!)

 

The "check engine" light is associated with emission control systems, most frequently the gas cap.

 

I think that OP's question was whether the scanner still draws power after the car is shut down. It is not a function of the scanner - it depends on the behavior of the ODBC port. Is power supplied to the ODBC port after the car is turned off?

 

The OBDII port is always powered up, even when the car is off. The Scangauge II turns off parts of itself when it doesn't detect impulses on the system for a number of seconds (I'm too lazy to look up the actual number). It actually is still partly on, but I doubt you would notice the extra current draw from the 12V battery. It's funny, because impulses from certain "battery maintainers" can turn it on, with the car sitting there off.

For the OP, watch to see if the battery is getting discharged faster with the new device connected. If it causes no problems after several days of the car being off continuously you're fine to leave it plugged in.

 

Makes sense!

My 12V battery ran down last time that my car was not used for an extended period of time. I suspected my ODBC connector. I now make a point of removing it if the car will be sitting for some time, and no further 12V problems.

 

A lot of OBD-II dongles are based on the ELM 327 integrated circuit, which has had a low power sleep mode for a while (introduced in v1.4b and of course still available in current v2.1). Whatever software or firmware is used in combination with your dongle also plays a part; the software can send commands to the ELM 327 chip influencing its sleep behavior. The ScanGauge II definitely does the right stuff to sleep at low power when not in use; your mileage could vary with other dongle/software combinations.

The hardware circuit design around the ELM chip can also have a large effect on how much power the sleep mode actually saves. Page 70 of the v1.4b data sheet goes through an example series of circuit refinements, where at the start they have a dongle that draws 31.9 mA in use and only reduces to 19.7 mA when asleep, and after a series of redesign steps, gets all the way down to 1 mA when asleep. That's a big difference, and some of it comes from using more expensive other components, like regulators, in the design, so possibly the dongles selling at very low price points won't have been optimized quite as much.

As you can see, the ELM 327 chip itself is a big chunk of the price of any cheap OBD-II dongle ... a big enough chunk that many of them use knock-offs of the chip. Whether the knock-offs match the genuine ELM chips in all specifications, who knows?

-Chap

 

I don't know what version of ELM327 I have, but I bought it about 4 years ago for $10 on Amazon. I measured the current consumption with a multimeter at 38.5 mA, which is fairly significant. The power consumption continues after the car is turned off. For reference, my 2006 Acura TSX has a parasitic consumption (power consumption while off) of 21.5 mA, which is probably about typical.

At 38.5 mA, a car that sits for 7 days without being driven will drain about 6.5 Ah from the battery. The Prius has a 45 Ah battery, so in theory you could go almost 7 weeks, but you don't want to drain even half of that or it will damage the 12v battery. This also doesn't account for the parasitic drain from the Prius.

I wouldn't go more than a week of letting the Prius sit idle with an Elm327 device plugged in. If you're planning to let it sit for longer periods of time, unplug it.

 

If you connect to your dongle using a terminal emulator, you should see the chip give a little version banner like "ELM327 v1.3a" when it first powers up, or any time you send it the command ATI. If you're using some fancy software like Torque with it, the software might have something on a menu somewhere to show you the version of chip it's connected to (where the software would send "ATI" to the chip, and show you the response).

Elm Electronics only makes chips. Usually when anyone talks about buying an ELM327 and plugging it into the car, of course they mean they have bought a complete dongle from some vendor that assembles a circuit board with the 327 chip and the other required components in a nice package with the connector to plug into the car, and a USB or wifi or Bluetooth interface, etc.

Since you can see that Elm charges $17 to $21 just for their chip, it is likely that any complete product sold on Amazon for $10 is built around a knockoff of the ELM327 chip, and not a genuine one. (Granted, I don't know how far Elm will discount their chips to a volume buyer, but there are definitely knockoff chips out there and likely to be found in the lowest-priced dongles).

That figure looks about right for a fully powered up dongle, judging by the discussion on p. 70 of the v1.4b datasheet. If that stays constant even after shutting the car off, then this dongle you've got is either (a) using a pre-1.4b ELM327 chip that has no sleep mode, or (b) using a knockoff chip that has no sleep mode, or (c) using a chip that has a sleep mode, but either the dongle hardware or the software you're using with it doesn't have the right provisions to enable it. My money's on (b).

You can see from the datasheet that with careful dongle design and a v1.4b or later genuine Elm chip, it should be possible to get down to 1 mA during sleep. But given the price of the genuine Elm chips, not to mention the other components needed to get the sleep current down that low, such a dongle is probably not going to be selling on Amazon for $10.

I leave my ScanGaugeII plugged in all the time. I've honestly never opened the case to see what chip's inside, but the SGII retails for more like $160 which means they can afford to use the good stuff, and in operation it's obvious they took the trouble to get the sleep mode right.

By the way, I have an older generic dongle (for use with a laptop) that came with a genuine Elm chip but an earlier version (the dongle was about $50, I think). When Elm came out with v2.1, I was able to just buy the chip and swap it in (the dongle circuit board had the chip in a socket) and start using the newer features.

I'm not sure if that's always an option for dongles using knockoff chips; it's possible the pinouts or electrical properties might not exactly match, and the least expensive dongles probably don't bother with sockets, and solder the chip down.

-Chap

 

I'm quite certain from what you say that I have a knockoff chip, and that probably accounts for the high power consumption. I think official Elm devices still go for $50. I'm also certain that my device has a soldered chip instead of a socket.

I'm curious, what features are added with later versions of Elm327? Since I use it all the time, I might consider buying a new one if the added features are neat. I should probably just buy a handful of the cheap ones to give to friends that ask me to diagnose their engine codes. Seems crazy to me that people don't all own these devices.

 

ELM327 OBD to RS232 Interpreters - Version History

It's been a year or so since I was getting my hands dirty, but IIRC a lot of the improvements involved the chip being able to handle more parts of the fancy protocols for you. It also has a more flexible sleep mode than v1.4b; your software can tell it specific kinds of bus traffic to watch for to control sleeping and waking up.

-Chap

p.s. oh yeah, I remember now, one of the improvements was support for more baud rates; the Prius Gen 1 has multiple computers sitting on the same bus that talk different OBD protocols at different baud rates (so much for any hope of talking to them at the same time!) and until I got the v2.1 chip there were some ECUs I could never get any response from.

Then of course my Gen 1 got wrecked, so I probably won't be making any more progress in those investigations....

 

I'm finding it impossible to tell which products include v2.1 chips, let alone which products have genuine chips.

 

Right, that's the trick ... if you could get the product in hand you could maybe tell.

There is a prominent alternative source of those chips that it's maybe not quite fair to call just a knockoff: scantool.net does their own chip family (the STN family), which are positioned as ELM327-compatible but not just clones; they have their own added features and improvements.

If you have something with an STN chip and you send it an "ATI" command, it will reply with an ELM327 version string, because that's what it's pretending to be. But if you send it an "STI" command (which would mean nothing to a real ELM327), an STN chip will send back its own real version string.

Of course there are probably offshore clones of both chips, which might even answer back with an ELM and an STN version number, and still not be genuinely either one....

-Chap

 

I notice scantool.net gives pretty complete specs for their family of dongles, including the current draw when asleep.

They used to sell some based on 327 chips from Elm (that's where I got my old one, with the socketed chip), but I think all of their products now are based on their own STN chips. At least, the bottoms of all of their detail pages include links to the STN family datasheet.

That saves them the expense of a socket, since their STN chips are firmware-updatable.

-Chap

 

There is an old wiki page for the Torque app that lists compatible dongles, and the highest rated ones are from scantool.net. I don't know if the info is up to date, or if there are cheaper options that provide similar performance.

Would I need the MX dongle (can access GM SW-CAN & Ford MS-CAN networks in addition to standard OBD-II protocols.) if I wanted to use it on the Chevy Volt or upcoming Bolt?

I've got a camelcamelcamel.com price watch on them because I feel that $50+ is too much to spend when my $8 one is working fine.

 

I have the ScanTool.net OBDLink MX Bluetooth adapter from when I was using it and Torque to monitor the traction battery voltages on my former '05. It was the highest rated adapter at the time because it was the fastest Bluetooth adapter available (in PIDs read per second). This adapter probably won't work with an iPhone because it's not a Bluetooth 4.0 LE device; they have a WiFi model for iPhone.

The STN chip reports ELM v1.3 compatibility, even with the latest 4.x firmware for my revision 2 hardware. On the plus side, it seems that the Carista developer has added some support for the ST command set, because Carista was able to use the MX to set options on both my Gen3 and Gen4. It otherwise requires a chip with ELM v1.4a compatibility.

 

You guys are amazing, I mean this thread, helped me out a lot. I own an old (-02) Corolla Verso, and since we live close to everything and love bicycling we use the car on average once a month. I occasionally check the battery status and although it starts after a month of resting it's lit "orange" on my tester, even though I recharged the battery fully with a trickle charger before the last run. I was worried that either battery's due to replacement, or (worse) I have a serious electricial issue in the vehicle, with something stealing current. Last thing I'd suspected was this cheap "V-gate Pro" Bluetooth OBD2 dongle that I keep plugged in. Today I noticed that it's blinking constantly, even though the engine is off, no ACU whatsoever. Hopefully this was my problem. I have now unplugged that dongle. The car will probably stand on our parking lot for another month, and then I'll check battery status again. I'll get back with a report!

Skickat från min ONEPLUS A3003 ?

 

Some bluetooth adapters have an on and off switch.

 

I have an OBDII Carista scanner on my Gen 4 and can confirm that it is always on, but the parasitic draw is very, very small. I would unplug it if I was leaving the car unused for a long period.