A Mini-OBDII Scanner for the Prius

The Prius Mini-Scanner is a device that reads information from the computers in a Toyota Prius and displays it for your edification and delight.  The instrumentation provided on the Prius is quite rudimentary, especially given the technology in the car's powertrain.  The Prius Mini-Scanner augments the built-in instruments with engine r.p.m., coolant temperature, traction battery current and state-of-charge and much, much more.  You can mount the Prius Mini-Scanner behind the steering wheel where most cars have their instruments.  It connects to the car using the existing "OBD-II" diagnostic connector and can be left in the car at all times.  You do not need to cut any wires or modify the car in any way to install a Prius Mini-Scanner.


The Mark II Prius Mini-Scanner will be available for purchase in early February, 2004.  For complete information on the Mark II, please visit http://miniscanner.ecrostech.com (at my "company" Web site).  The remainder of the information at this site refers to the Mark I Prius Mini-Scanner, which was produced in limited quantity only.  Some Mark Is may become available as owners upgrade to the Mark II and this information will also appear at the new site, above.

The main differences between the Mark II and the Mark I are:

Installation and Operation

A practical way to install the Mini-Scanner in the Prius is to put it behind the steering wheel, where most cars have their instruments (see picture at right, Mark I shown).  Although you can install the device in other ways or just leave it hanging loose for passengers to play with, I have written up the installation guide assuming this standard method.

The User Manual describes in detail how to operate the Mini-Scanner.  I will keep this document up-to-date with respect to the latest firmware release.  If you are running an older version of the firmware, some of the functionality described may be unavailable or accessed in a different way.  It will take several months to write the firmware to deliver the full intended functionality.  However, the Mini-Scanner is field upgradable with new firmware, so as long as you have a serial cable, you will be able to update as new functionality becomes available.

Updating the Firmware

How the Prius Mini-Scanner works is mostly defined by software running on a microcontroller (a very small microcomputer with everything on one integrated circuit or "chip").  A memory inside the microcontroller stores the software, holding onto it even when the power is turned off.  For this reason, the software is often referred to as "firmware".  Nevertheless, it is possible to change the Mini-Scanner firmware to take advantage of new functionality and fixes for any problems.  Firmware is updated using the Flash Loader, built into the Mini-Scanner during manufacture.  The ability to update firmware after shipment to the user was a requirement for the Mini-Scanner design and you can also read the original specification for this feature.  The most recent version of the firmware is available for download, as are significant earlier releases.

Frequently Asked Questions (FAQ)

I have gathered together some questions asked by prospective users of the Prius Mini-Scanner into a Frequently Asked Questions section.  Please take a look here before sending questions to me by e-mail.

How You Can Help

I still need help with this project.  This is what I need:

Miscellaneous Links

Last edited January 9, 2004.  All material Copyright 2003 Graham Davies.  No liability accepted.