Feb 262012

ELM 327 Bluetooth OBD2 Adapter

Just purchased a 2012 Prius V (why have I not written about that yet?) and one of the more active topics on the PriusChat forums is how to disable the annoying backup beep that sounds continuously while you are in reverse. Now, you might think that a backup beep is a great feature. Only problem is this beep is very loud and is only inside the car! It cannot be heard by those behind you as you would expect.

In the previous Prius incarnations you could hold your tongue a certain way and press a series of dash buttons along with your key fob to disable this ‘safety’ feature. Now, Toyota says to take it to your local dealer for them to make the change. Only problem is many dealers don’t even know it can be done (or at least the people you and I would talk to don’t) and many new owners report that the dealer wants to charge anywhere from $50 to $100 to do a 2 minute job. Some dealers do the right thing and turn it off free of charge but some only do it after the owner called Toyota corporate and complained.

Me, I know my dealership would do it if I asked but why have them do something that I can waste hours figuring out for myself. First, I needed a way to talk to the car’s computer. I had already bought ELM 327 Bluetooth OBD2 scan tool from Amazon that plugs into the ODB-II slot under the dash so I could monitor some of this little hybrid’s inner workings (here is another post I should have written). The device uses bluetooth to communicate to the outside world and wouldn’t you know it, a number of Android apps have been written to accommodate. (Note: Seems that the OBD2 port has a constant power supply, so even if you turn the car off the device stays on as does the Bluetooth, so probably best not to leave it plugged into the car overnight any more than you would leave your dome light on.)

Seemed like this little scan tool should be able to send data as well as receive, so now I just had to figure out how. I tried using the android ‘Torque’ app that I was using to monitor the vehicle but had no luck then I remember I had seen a program called ‘ELM 327 Terminal‘ which claimed to allow you to communicate with the ELM 327 adapter, sending commands to your hearts content. My first attempts to just send the strings I had seen in the forums did not work. Then I ran across a post explaining how to send these commands to a USB connected ELM327 device using a laptop and a terminal program and figured the same commands should work with the ELM 327 Terminal Android app as well.

Out to the car. Plugged in the ELM327 device. Activated Bluetooth on my phone and told the terminal program to ‘connect’. I had the terminal program send a AT I command just to make sure I was communicating with the device. Now I crossed my fingers and hoped for the best. I turned ‘Timer’ (right side of screen above ‘clear’) off otherwise the command you send gets sent over and over again. (Not sure it matters but in case it does, I had the car ‘on’ with the ‘Ready’ light showing and all the doors were closed.)

First we need to tell ELM327 where to direct our commands, in this case we want to talk to ECU (engine control unit?) 7C0, the combination meter.

Type: AT SH 7c0 (hit ‘Send’)
Returns: OK

Type: 21ac (hit ‘Send’)
Returns: 61 AC 00 (00 means continuous reverse beep)

Type: 3bac40 (hit ‘Send’)
Returns: 7F 3B 78 (no idea :)
Returns: 7B AC (meaning done)

Type: 21ac (hit ‘Send’)
Returns: 61 AC 40 (40 means only a single beep now)

Now for the real test, I popped the Prius into ‘Reverse’ and joy! joy! only 1 beep. Guess now I will have to figure out what other options I want to configure.