-- This page has about a meg of image data, and WILL take time to load --
WARNING: disconnecting wires in this area is likely to have the same
effect as disconnecting the 12V aux battery -- settings such as radio
stations, clock time, beep enable/disable, power-window calibration all
get un-set and you have to put them all back the way you wanted afterward.
_H* 050913
Prius body ECU disassembly
This describes a somewhat surprising journey inside that white chunk of
plastic mounted up under the left side of the dash. It was motivated by
desire to find the right interconnects and hack up a way to enable the
power windows without having to go to IG-ON, and also to allow the remote
unlock fob to still work with the car powered up. Both functions are
managed by the body ECU, and many of its interconnects are completely
internal to the connector block it's buried inside. There's nothing
particularly useful in the service manuals about it. Thus, exploration
is clearly needed.
The "Driver side junction block", as it's called, mounts to the dashboard
strut and the side frame piece with three bolts. The harder part is undoing
all 18 connectors from it. Connector 1E, in particular, has a little green
bar of plastic run through near its upper end which cannot be backed out
until the whole J/B is moved away from a nearby metal brace. [The plastic
bar is on the floor just ahead of the seat.] Eventually the block can be
extracted, bringing the whole fuse block and three large relays down with it.
Now that the damn thing is finally out of there, we bring it around back
for clearer workspace. This is the side away from the driver. There are
four or five fairly obvious pry points to release the plastic cover. These
should be brought out evenly, without tilting the cover too much.
Aha! Here's the body ECU. The three external connectors [B5, B6, B7] are
mounted directly on the circuit board, and the long thin one is the internal
connection [unlabeled] directly into the J/B. Here
is a detailed closeup of the board. [huge!]
Removing four screws allow us to pull the board off its internal connector
pins and view the back side. Here is a closeup of
this side. [big!]
But we're not done -- this thing keeps going and going, like an onion. The
next layer of plastic turns out to *BE* the connector housing, and can be
extracted fairly easily -- leaving all its pins behind. They all just slip
down through the holes. We're VERY careful not to bend them, or realigning
all this will be difficult!
Next, after removing the relays and fuses on the front, the entire block of
connections can be pulled out of the shell -- again, bringing all the pins
with it. Talk about a custom molding job... It is immediately obvious that
the connector block is composed of two layers, which appear to be trying to
separate a little bit.
This is the really scary part: most of the interconnects between pins
are done with INSULATION DISPLACEMENT connectors and solid wire. This is
really surprising given the vibration potential of the surrounding
environment and some of the heavyish currents running through these
connections. At least the really high-current stuff lower down is done
in one-piece stampings that are in little danger of coming apart.
Here's the closeup of the IDC swamp. [sizeable!]
It is interesting that the wire ends are also run to slits in the plastic
edge of the block -- extra anchor points. Likely that the entire thing
is produced by machine, rather than human hands.
The halves won't separate until the fuse block part is removed. Which
requires pulling all the fuses, and making sure the legend on the cover
matches what we find...
after which the fuse holder shell drops off, leaving all the contacts. Now
we can really see the bus structure for the fuse tree, as documented in the
"power source" section of the EWD. The feeders are spot-welded to some of
the high-power buses on the front of the unit.
Another attempt to separate the halves is stymied by the fact that some of
the fuse connectors attached to one half run underneath, and interfere
with, connectors from the other half. At this point it looks like one
would have to bend or break the spot welds to continue, so this is where
it stops for the moment. Note, however, the height difference between
various sets of pins -- some are attached to one half, and some to the
other, and everything evens up when the halves are put together.
It almost felt like the bus-bar section wanted to separate away from the rest
at this area, but it was impossible to tell if that would begin pulling
some of the wires out of the IDC connections. I didn't risk it. However,
having the unit this far apart did allow tracing some of the internal
connections and determining [by powering them and hearing the click] that
some relays really are embedded deep inside this thing, under the bus-bar
panel. I couldn't even wedge things apart far enough to *see* them. This
implies very difficult serviceability if, for example, the "PWR" relay for
the power windows goes bad ... but of course Toyota's answer is "Replace
body ECU" and gouge the customer for four digits.
It's all installed back in the car again by now, without any problems.
Initial debugging results for the intended hacks are less than stellar.
Enabling the power-windows relay via the 45-second-delay "KOF" line at ECU
internal connector pin 13 lets all windows EXCEPT the driver's work,
which isn't entirely useful. And from what I can determine the RF fob
receiver always receives data and sends it to the ECU, but when the ECU is
powered up in IG-ON or READY it completely ignores the data. In general
the architecture around the body ECU lets it retain way too much control
over the functionality, but perhaps that is deliberate since it *is* also
a security component.