In order to supplement the inadequate-by-design alternator BIT circuits in my 98 Avalon (alternator failures have stranded us; no instrument panel warnings of charging failure), I'd like to either monitor the battery bus at the cigarette lighter (possibly a homegrown device to activate a piezo or flash an LED) or monitor via the OBD2 port with smartphone app alarms.

I looked at a list of obd2 fault codes and didn't see one for battery bus voltage. I found the list via a google search and it was on toyotanation.com.

Bluetooth and an app where you could set alarm for a voltage threshold is the general idea (say 13V or less for 5 or more seconds while the engine is running). The obd2 scanner would have to go to sleep and not drain the battery as I'd like to leave it plugged in 24/7.

Is battery bus voltage available via OBD2 scanners for the 98 Avalon? Has anybody had success using an obd2 scanner for full-time engine performance monitoring of an old Toyota, including battery bus voltage?


  • 1
    IIRC the PID is available. It would be better to tap into the alternators lamp circuit or buy a digital volt meter that plugs into the lighter/accessory socket than to rely on OBD2. As far as monitoring engine performance you can but you'll run into problems with the speed of the serial data bus. Unless you're looking at a handful of PIDs at a time it basically updates once every couple of seconds.
    – Ben
    Commented Jun 14, 2016 at 20:00
  • I don't know whether OBD has a fault code for low battery voltage, but I'm pretty sure at least some models have the voltage available as a "measuring block", so your app can just poll that and trigger an alert if it goes too low. However using OBD for this is way more complicated than it should be, as you can get away with a simple analog circuit connected to the cigarette lighter port that would cost only a few dollars in parts. Commented Jul 4, 2016 at 14:58


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