RE: Traction Control / Overdrive Default off Module- working prototype
In a Gen 2 vehicle, you need a pulse on 2 switches, not just the one. After startup and then after the prove-out of the message center, you need to press the vehicle setting switch and then the reset switch. The EVTM does not show what is needed. The manual shows 2 wires coming from the message center, going into the switch assembly which shows each wire has a variable resistor on it connected to ground. So, if that is the case, the 2 wires probably use 2 pull-up resistors built into the message center (to keep the wires at or near 12 volts with no switches pressed) and then as each switch is pressed, a different voltage would appear on the one wire associated with the switch, depending on resistance or the resistor connected to the switch. That would change the voltage coming from the message center.
You would need a delay circuit, which you already have using a 555 timer, but then you would need to know what wire goes to what switches and what the resistance is on the wire - say when you pressed the "vehicle settings" button. Then you would need the same information when the reset button is pressed.
I have done some preliminary testing on my '98. It seems you do need the delay circuit because the message center will not even show "traction control" in the message portion until the T/C lamp is out after turning on. It also turns the T/C back on if it is already off and you decide to start the car instead of leaving the ignition just ON. You obviously need +12 volts for this circuit and the best place to get it is the Instrument Panel Warning Indicator Display, specifically from I/P fuse 5 which feeds the MIL. This is active only in run and start and is conviently located on the same switch panel, which is the easiest to modify. There are also other places on that panel to get voltages, but the one I specified will not be on in Accessory. Just pop it out, make 4 connections (at the most) and nylon strap it right in place.
The Gen 2 vehicles do things a little different ( hell, a lot different) than a Gen 1. Gen 2 has a system called a SCP or Standard Corporate Protocol in it. It is supposed to save on wires. For example, there is just one connection to the vehicle's speed sensor and that is to the cruise control. It then uses the SCP (which is 1 or 2 wires) to give that information to any other module that may need it, like the speedometer, the traction control, etc. There are many signals traveling all around the car that we are not aware of and it uses this method. One other use is the traction control ON/OFF. The switches turn the message center's display to ON or OFF, but using the SCP, the signal is sent to the traction or 4WABS module to turn it on or off. There is no other connection between the switches and the ABS module. There is a separate connection between the message center and the T/C lamp. It is a grounding pulse for about 3 to 4 seconds at startup. And as I said, nothing can be done to the T/C until this light goes out.
It would be easiest to do this at the switches, where the action is at least easily or easier to duplicate. Three pulses are needed. A delay as you already have and 2 more positive pulses at different voltages and/or different wires.
They show variable resistors in the drawings, but I'm sure they use standard value resistors connected to each of the 7 switches to do the connection to ground.
I'll get you more information as soon as I can. I have a project to get out of the way first. A scope is probably not needed. A 1/2 to 1 second pulse is probably just about right. 4 seconds for the delay.
If I can, I'll pop the switch panel out and measure the resistances on the 2 switches and tell you which of the 2 wires they are connected to. You can then take it from there. Since I don't have posi, I don't need it.
