Untitled Document

7/30/06

First, let me say that Vehicle Stability Control (VSC) isn't all bad. In the rain, snow or emergency manuevers it could come in pretty handy. However, for any kind of performance driving it is a hinderance to extracting the full ability of the vehicle. It also makes the steering and throttle feel very vague, not mention creating a car that pushes in the turns and fails to accelerate out of a corner. Lighting up the tires or trying to drag race at the track will also be frustrating.

So what to do? Lexus has seen fit to provide a button called "Trac Off". What is deceptive to most Buyers, me included, is that this function only works below 35mph when VSC is least needed anyway IMO. There is another option available, Dyno mode! The only saving grace in an otherwise disasterous Lexus idea. Dyno mode can be accessed by a series of brake and ebrake activations known in Lexus circles as the Pedal Dance. It is a cumbersome and somewhat demeaning operation to have to perform on one's $40K car. It does, however, turn off the VSC completely until the car is switched off.

To make this process more simple, I designed and built a microprocessor based controller to signal the car's ECM into Dyno mode. After much experimentation, the first prototype is currently being tested. So far, so good. The unit is installed under the dash and taps into several leads in the wiring harness of the car.
The unit is currently activated via a separate button I installed in the dash using a spare blank from my 4Runner. The procedure is: Start the vehicle, release all brakes, depress the button for a few seconds until the VSC light illuminates on the dash, and then drive and enjoy.

The obvious question from everyone is, "Will I be able to get one too?" The answer is, at this point this unit will be available to the public in design specs only. The dilema with such a device is that it will only be intended to off highway racing purposes. Use of such a device will cause vehicle and property damage as well as personal injury. It will void your warranty and destroy your vehicle's electrical system. It will cause you to do stupid things in and to your car along with a bunch of stuff I and you haven't even yet imagined.

Having said that, I hear the 2007 Lexus IS will have a proper defeat button. Hurrah for the '07 Buyers. Here are instructions on building one. Please refer to the crudely depicted schematic that lists Radio Shack part numbers where appropriate. Lines highlighted in red were jumpers on my PCB and not traces on the PCB.

3A fused +12V flows through a momentary switch, to the input of a LM317T (276-1778) voltage regulator. A 0.1uf capacitor bridges to ground from the input to clean up the switched input voltage. The output of the LM317T connects to the +9V bus running down the center of the PCB (276-150). To regulate to this voltage, a 100 ohm resistor bridges to the Adjuster lead and 620 ohm bridges to ground from there. This produces 9V output for the 4017 chip. All other components are not voltage specific. A 7809 regulator would have avoided the 100 & 620 resistors but I couldn't find one.
Signaling begins at a 555 Timer chip on the left side. Pin1 (Gnd) also bridges to Pin2 (Trigger) with a 10uf 16V (Watch the polarity). Pin2 jumps to Pin6 (Threshold) and bridges to Pin3 (Output) with a 27K resistor. Pin3 drives Pin14 (Clock) on the 4017 (B series). Pin4 (Reset) jumps to +9 bus. Pin8 (+Vcc) jumps to +9 bus.
Output selected strobing is done with a 4017 Counter/Divider CMOS cpu. Pin1 (Output 6) & Pin6 (Output 8) ultimately drive the "Red/Blue" leads. Pin2 (Output 2) & Pin7 (Output 4) ultimately drive the "Black" lead. Pin8 (Gnd) jumps to the Ground bus. Pin9 (Output 9) jumps to Pin15 (Reset) to initiate an early reset of the counter. Pin13 (Latch Enable) jumps to Ground to force counting on high signal. Pin16 (+9V) jumps to regulated bus.
Red/Blue leads refer to the Red and Blue wires on the main brake switch that signal the car's ECU. See picture. A tap from each runs to the PCB board from the brake switch. The Pin1/6 outputs are bound together and are tied to the base of an NPN Transistor (276-1617) to amplfy the signal with the emmitter connecting to one coil lead on a 275-241 Relay (#1) and the collector leading to Ground. The other coil lead jumps to +9 and a 1N914/1N4148 Silicon diode (276-1122) bleeds off coil load when the transistor opens by jumping the coil leads together. Note the reverse diode connection to bleed reverse voltage. The Red lead ties to the NC Relay connection. The Blue lead ties first to one switched lead on a NO 275-233 relay (#4); the output of which jumps to the input of the pulsing 275-241 relay. The NO 275-233 relay (#4) isolates the Blue and Red when the VSC defeat unit is not in use and it only closes when power is supplied to the VSC defeat module via the momentary switch.
The Black lead refers to the control lead on the parking brake switch located on parking brake bracket up high against the firewall. It's a pain to get to and find. When grounded it turns on the parking brake light as well as signaling the car's ECU. See picture. As in part 4, the Pin2/7 drive an amplifying transistor to a 275-241 relay (#2) . A lead is tapped in the Parking brake switches lead to the NC connection on the relay. The input to the relay #2 comes from another 275-233 isolating relay (#3) that activates when power is supplied to the VSC defeat module and then supplies a ground signal to the pulsing relay.

So there you have it. A module that will signal the 2006 IS250/IS350 to turn off the VSC. Unfortunately I don't have the time, inclination or desire to expose any liability in constructing the module for others. BUILD IT AT YOUR OWN RISK. I do have about a dozen extra 4017's which are hard to find but you can try http://www.electronics123.com and misc extra parts I will sell to the first takers. When they are gone, that's it.