Auto Down Power Windows....
Why can't I have it for the passenger side, too?
by Blitzo


Intro:
Every Spyder owner quickly finds the driver's window auto feature and most appreciate its convenience.  And sooner or later, most wish this feature was present on the passenger window as well.  And what about auto up?  The auto down feature is so convenient, why not make it go up automatically, too?  And what about that 'retained power windows' feature that was listed on both the 2000 and 2001 models, but not delivered?  Other Toyota models have this feature, why not ours?  Just how hard can it be to add some of these features to our cars?  I can't answer all these questions, but I will do my best to answer some of them.

 

The Driver's window switch is P4 on the left, the passenger's window switch is P5 on the right.
Driver Side Auto-Down for the Passenger Side:
The first reaction to the passenger side problem is to say "Well, I can add the auto-down to the passenger side by just switching out the passenger switch for another driver's switch I buy at the dealer.  Unfortunately, this won't work for several reasons.  The first reason, is the connectors are different.  They have a different number of pins and a different configuration.  So even if you had another driver's switch, you can't just plug it in.  You could buy another wiring harness connector for a driver's switch and modify the passenger harness to be able to plug into a driver's switch, but the wiring signals are different and you still couldn't make it work.

 
This is a look at the schematic diagram of the power window control system.  Note the drastic differences between the circuit for the driver and passenger windows.
The second problem is that the auto-down function is not in the switch itself, it is in the body computer under the dash.  So even if you did manage to reconfigure the wiring harness, you still have no electronics to be able to control the automatic window functions.  

One interesting characteristic of DC motors is that while they draw a certain amount of current in operation, they will draw a much higher current when the motor is stalled (no longer moving).  The body computer measures the current being supplied to the window motor and senses when the small amount of current used to roll the window down (2 amps) suddenly jumps way up when the window bottoms out and the motor stalls (13 amps).  The computer shuts off power to the motor about a quarter of a second after it sees the motor has stalled.

I'm quite positive Toyota did not implement an auto-up feature simply for liability reasons.  After all, the motor has to come to a stop before the computer senses that it is time to turn the motor off.  And by then, fingers and other body parts could be quite painfully squished in the window.  And the way the body computer and wiring harness is set up, there is no easy modification to enable this type of feature, either.

 
This is the body computer circuit board - all relays and a single micro controller.
What's inside the body computer:
The body computer has a few primary functions:
bulletControl power to the window switches
bulletAuto-down for the driver's window
bulletManual up and down of the driver's window
bulletThe passenger unlocks both doors function
bulletThe driver single turn unlocks driver's door
bulletThe driver double turn unlocks both doors
bulletKeys in ignition unlocks locked doors if driver's door opens

The technology inside of it is all relays and power resistors.  Fujitsu automotive relays are used for the door solenoids and the both window motors.  A resistive bar (probably 0.05 Ohms) is used to sense the current on the driver's window motor.  A proprietary micro controller orchestrates the whole works.  There's not a whole lot that can be done the physically modify the body computer.

 
Retained Power:
Many other Toyota models have a retained power windows feature that the Spyder is advertised as having, but doesn't.  Anyone up for a class action lawsuit?  This feature keeps the power to the power windows alive for 43 seconds after the ignition key is turned off, or until one of the doors is opened.  Why 43 seconds, or why opening the doors cancels the feature is beyond me.  No wiring changes are necessary to enable this feature, just a change in the operation of the body computer.  Maybe we will get lucky someday and discover some secret way to enable this feature by opening and closing the doors a certain number of times similar to the way the keyless remotes can be reprogrammed.

The power coming from the separate driver and passenger window fuses are powered all the time.  Because the electronics do not enable power to the switches unless the ignition is on, they draw no power while the car is off.  It is the gauge signal that determines if the power windows should be activated.  If you could keep this signal active all the time, then your power windows would always work.  The problem is that the fuse line draws 260 mA and would run down the battery in about a week.  The gauge line is a signal source, not a power source (then why does it draw 260 mA?).  As long as the gauge signal is at least 2.0 V, the power windows will remain active.  If you could attach a simple circuit (capacitor and diode) to the fuse line coming into the body computer, you could have the windows active until the capacitor discharged below 2.0 V.  Once again, the current drain kills this idea, as we would need a gigantic capacitor to keep the voltage that high for a reasonable amount of time.  I experimented a bit with this and found that a 6600 uF cap would power the windows for about 15 seconds after shutting the engine off.  A 22,000 uF cap would keep the circuit alive for about 45 seconds.  The cap should be rated for at LEAST 28 volts - twice the 14 V max it would see.  A cap this large is about an 1 1/2 inches long and 1 1/2 inches in diameter.  There is room to shove something that large under the dash, but it's not my idea of fun. A time delayed-off relay would be ideal for this problem.

 
This product claims to provide auto up and down for all electric windows.
Possible Solutions:
While the retained power is not terribly difficult to solve, the solutions are not so elegant.  The auto up and down features have a completely different solution.  There are a few ways to address the problem. 

The simplest solution is to use an aftermarket system designed to work with remote keyless entry and alarm systems.  Many top end alarm systems will have add-on modules to allow the remotes to raise and lower the windows.  With additional logic and wiring, they might also be able to perform auto up and down as well.  I do remember seeing an advertisement in Sport Compact Car for a product from a company AutoLoc that provided 'one touch express' power window control.  I have not looked at this product, but it sounds like it will do the trick.  Maybe I should look into this a bit further.  It might end up being a decent $35 solution.

The most complex solution is to replace the entire body computer with a unit that will provide the desired retained power, auto up and down on multiple windows.  I looked into other Toyota models that had some of these features, but the body computer systems on these other models are completely different and I could not see a quick substitution fix.  Besides, these body computers run about $300 each, so this is not a desirable route for many reasons.

A mid-range solution is to partially replace some of the functionality of the body computer (window functions) and let the body computer continue to control the rest of it's functions (door locks).  The only hitch with this approach is that the driver side functions are controlled at the body computer under the dash, and the passenger functions are controlled at the passenger switch itself.  That means two separate modifications in two separate places, and that sounds like double the work.

 
Conclusion:
As you can see, there is no simple solution.  I am not satisfied with the operation of the Spyder's windows and I for one will be doing something about it.  But that's another story....