[chbot] Prius status report and a request for information.

Peter Harris petes.username at gmail.com
Mon Jul 27 02:29:11 BST 2015

Hi All
For those of you who weren't at the July meeting I have purchased a dead
2002 Prius with a view to learning about the battery system & getting it
back on the road.

The first course of action was to if there was any life in the traction
battery. Disclaimer: this is a 300Vdc system with the power to kill you
dead on the spot, cause fires, explosion and all the related mayhem. If you
don't no what you're do then don't do it.
(Proceeds with butt suitably covered)
It is possible to gain access to the main ~300V battery voltage by means of
a secured service cable while the battery is in the vehicle. The procedure
1> Remove service plug to disarm the battery.
2> Remove the secure cover protecting the service cable.
3> Secure volt meter to service cable making sure the connection is stable
and safe.
4> Replace the service plug to arm the battery and read the voltage.

I diligently followed these steps with gloved care and attention expecting
a voltage between 200V & 320V and was a little disappointed to get a
reading of 1V!

The battery clearly required closer examination so youtube videos were
watched and the pack was removed for inspection in my shed. For reference
it took 90 minute to get the 53kg battery out and into another car for

Once the battery was opened it was quickly determined that all 38 of the 6
cell NiMH modules were at ~0V and had minor corrosion on the terminals.
Further investigation showed that the cells were in a dormant state and

At this point a fault was located. There is a wiring harness carrying 20
voltage sense signals from the battery stack to the battery management
computer. There has been a small fire in this harness where it is connected
to the computer module. (I attempted to include a picture here but was
thwarted by the post size restriction. I shall have to use a thousand words
The pictures shows a orange multi-way connector with a charred hole at one
end an some normal connections at the other.
If you could see the picture you would see a dozen or so cables &
connections have been destroyed, fortunately the damage seems to be
localised to connector. The plan for repair is to remove the connector
entirely and build a new harness soldered directly to the PCB. The problem
is that battery management computer has 26 voltage sense inputs on this
connector while the battery only has 20 signals. Two unused inputs can be
seen in the picture I need to identify the remaining four.

*HELP needed:*
I am looking for a diagram of, a picture of or access to this harness as
used in a generation-1 Prius.

Aside: I've found 2 reports to charring & fire at this location possibly
related to humidity. Direct soldering and potting should prevent further

Best regards
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