[Ovmsdev] Nissan Leaf

[Tom Saxton]

I bought a tiny $12 ELM327 Bluetooth gizmo that's listed among the devices
compatible with LeafSpy.

http://www.amazon.com/gp/product/B008U1MOM8/

I also bought the OBDII Y cable that Mark suggested which looks like a high
quality cable and it works.

http://www.amazon.com/gp/product/B00EEDOWU8/

At first I had zero success getting CAN messages from the Leaf's CAR-CAN bus
using the ELM327; I got either nothing or garbage data with errors and
buffer overflow messages.

This tutorial Mark suggested is inspiring, and illustrates a good general
technique for figuring things out, but it has no information on how to get
CAN data.

http://theksmith.com/technology/hack-vehicle-bus-cheap-easy-part-1/

I was then led astray by reading the ELM32X data sheet and the Wikipedia
page on how OBDII CAN messages work.

http://elmelectronics.com/DSheets/ELM327DS.pdf
http://en.wikipedia.org/wiki/OBD-II_PIDs

The specifics of how the messages are formatted is completely wrong for the
Leaf. The 11-bit CAN ID values are not used to identify ECUs, they are the
message identifiers. Instead of looking at CAN IDs in the range 7E0 to 7EF,
you have to look at all CAN IDs from 001 to 7FF.

The next problem is that there is so much traffic on the Leaf's CAR-CAN bus,
that a low-bandwidth unit like the cheap Bluetooth gizmos can't possibly
keep up. I was able to determine that the output baud rate on the above
gizmo is at most 38400 bps. To look at things, you need to filter to only
get a subset of the constant stream of traffic on the CAR-CAN bus.

The trick is to use the ATCM (CAN mask) and ATCF (CAN filter) commands to
filter for a single message. For example, to view message 0x5C5 which
includes the Leaf's odometer value, first set up the chip with these
commands:

ATZ
ATH1
ATL1
ATS1
ATAL

Those commands in order: reset the chip to defaults, turn on message headers
(which show the CAN ID), line endings between messages and spaces between
bytes, and enables long messages. Then issue these commands:

ATCM 7FF
ATCF 5C5
ATMA

The first two commands set the ELM327 to filter for a single message ID,
5C5, the third starts dumping them. You'll get data that looks like this:

5C5 44 00 3C BA 00 0C 00 00
5C5 44 00 3C BA 00 0C 00 00
5C5 44 00 3C BA 00 0C 00 00
...

Type any character to stop the spewing of messages. The first group of three
hex digits, 5C5, is the message ID, followed by the message data, bytes 0
through 7. According to the LEAF CAN message spreadsheet, skipping the first
byte (44) and taking the next three (00 3C BA) yields the odometer. Sure
enough, 003CBA is 15,546 in decimal, which is indeed our Leaf's odometer
value.

I also confirmed the Gid value documented in message 5B3 for several Gid
values in the low 200's.

To get an idea of what's happening on the CAR-CAN bus, I wrote a program
that marches though all 2048 CAN ID values, listens for each message ID
until either 20 messages have been collected or 2.01 seconds goes by with no
messages, then moves on to the next ID. Using that program, I found 49
messages that happen between twice and one hundred times per second when the
car is parked and turned on in accessory mode. Together, they total up to
over 1500 messages per second. So, you'd need an output baud rate around
500,000 bps to monitor all messages, which is totally not happening with a
$12 38400 bps gizmo.

I've attached a spreadsheet with the list of those messages. I have a text
file with 20 sample messages of each type. I'm happy to share if anyone else
wants to see it.

See the spreadsheet of known LEAF CAN messages to see what's known about
what they contain.

https://docs.google.com/spreadsheet/ccc?key=0An7gtcYL2Oy0dGRaSWl6VTV2eXBQMy1
ON2xZSzlMUXc#gid=1

Unfortunately, with the sealed plastic $12 gizmo, there's no way to look at
the EV-CAN bus, so that will have to wait until I get a better device. I'm
considering these three:

Mark recommends: http://www.can232.com/?page_id=16 ($140 + cable + shipping)
Roadster service techs use: http://gridconnect.com/can-usb.html ($255 +
cable + shipping)
Sparkfun: https://www.sparkfun.com/products/9555 ($74.85 with cable and
shipping)

For connecting to the CAN bus, OVMS uses the same pin mapping as the device
Mark and Tesla use. Sparkfun uses a different pin mapping which agrees with
what OBD2cables.com says is the "de facto standard pinout."

http://www.obd2cables.com/products/cable-j1962m-right-angle-to-db9f-4-3-ft.h
tml

Standards are so awesome, we have at least two!

I was surprised to see obd2cables.com claiming a standard that's different
from what I expected from Mark's and Tesla's preferred gizmos. Fortunately,
it should be easy to make a DB9 adapter to convert between the two standards
should the need arise.

   Tom


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