let`s take control of the SWAS

I did a lot of reading yesterday about SWAS and the various ways people have been defeating it, and it all ends with dash lights on and potential abs/dsc defeat. I want neither of those. SO I dug into it a little more and got the sensor voltage defaults (ie; the voltage that tells the system where the wheel is pointed). Centered puts out .25 to .75 volts, and anything left or right does .75 to 4.75 volts. The very first thing I thought was "well f**k, why not just use a simple integrated voltage regulator to cap the output voltage at .75 volts?". Yes, it`ll work. It`ll work like a champ and completely solve all of the headaches associated with SWAS.

"So, Jef, what`s the catch? If there wasn`t one you`d have surely put that into action."

There is a catch, but only a little one. I can`t find anything lower than a 1.5 volt regulator. Given how sensitive the system is I don`t think it`d do any good allowing more than the .75 volts through. So I need one of two things to move forward: either a .75 volt regulator source OR evidence that the neutering is triggered at a higher voltage (the system giving allowance for X degrees off center). Again, referencing back to how sensitive the system is I`m betting that there is no wiggle room, but we can hope.

With that no on the table, what say you? Can we source the correct regulator?

 

Seems like you could use a 1.5 volt regulator and tie the output to a voltage divider to get the required .75 volts. All you'd need in addition to the regulator is a pair of equal value resistors.

https://learn.sparkfun.com/tutorials/voltage-dividers

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my only concern is current. Any time we drop voltage we raise current, and that could go badly. The signal from the SWAS goes to the PCM and sending too much current....RIP. But how much is too much in this case, and how much are we dealing with, and how much can the PCM read?

 

My guess is considering the center input is designed to sense 0-5v input anything in that range would not cause damage due to internal resistance of the pcm

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http://www.mouser.com/Mobile/Semico...Cs/LDO-Voltage-Regulators/_/N-5cgac?P=1ywxsbt

Maybe email them and see, they say their regulator goes to 500mV aka .5v

 

I drive right by Mouser almost every day. I really do need to just stop in and ask them.

 

I did a lot of research/experimentation on this and did a long write-up with lots of updates. It can be found here, if people want to know why disabling it is really desirable for lots of folks. BTW, SWAS unplugging doesn't disable ABS in my experience; DSC is a different story: https://mazdaspeeds.org/index.php?t...swas-disable-features-on-2010-test-mule.4004/

Having said this, a "fix" to remove the two warning lights would be very nice.

--- Double Post Merged, Apr 29, 2017 ---

If we're increasing resistance, it'll actually lower the current of the system (V/R) = I (see below), so long as we're using resistors. Resistors have been used to "trick" the ECU to think the VTCS is still operational after it's been removed on ported IMs, so it could work here too:



The trick is to keep the voltage in a specific range so that the system never thinks the steering wheel isn't pointing straight ahead. I'm thinking that just strong enough resistor(s) would do the trick because voltage is a function of ohms (resistance) x current (amps). Personally, I'd aim for right in the middle of the .25v-.75v range to account for voltage fluctuations in the car's overall power system, so what about .50v instead?

The question is, are we only talking about one wire this will need to be done to? Also, does the ECU/PCM have a failsafe function that'll trip a CEL if this system is messed with in this manner, especially if a resistor drops the voltage too low? And what about heat dissipation? I agree a regulator seems the way to go. Hunting for the right one too...

--- Double Post Merged, Apr 29, 2017 ---

Dang, it's hard to find a regulator with a 0-5v input and a 500mv output! Argh...

 

Yep, the absolute simplest solution that would require nearly no effort at all would be a 5v - 0.5v step down regulator. I`ll stop bt Mouser on monday and see what they suggest

 

Grabbed what I hope to be a useful page from the factory service manual:

It appears that Terminals A, C, E, and D should be limited to .50v. I say .50v because electrical components have variances of a few percent most of the time. So if we shoot for .25v or .75v and the variance takes it out of the range, SWAS may still interfere. That's my rationale regarding regulating the voltage to .50v (500mv).

But according to this, we may only have to worry about Terminal A (the light blue wire - the only one you address in installing a switch):
http://www.mazdaspeedforums.org/forum/f429/how-install-switch-swas-enable-disable-102406/

 

I always thought cutting one of the wires was to cause a fault and totally disable the SWAS.
From what I see above, I think to truly fool it and see that there is no angle change at all you need A & E to be 0.25-0.75V and C & D to be at 4-4.75V constantly.

 

Yes, cutting the wire disables the whole thing and puts up a fault code. The diagram seems to imply that each terminal is responsible for detecting progressive degrees of wheel angle. A seemingly more reliable system, but also more sensitive if they all trigger the same reaction (which I suspect they do, given how touchy the system seems to be for some folks). And yep, looks like A/E need to register the .5v and C/D need 4.5v. It also appears that we could leave terminal D intact and keep full swas function at a true steering angle over 3 degrees should we want that. A and E would be easy to wire in an inline regulator. C and D would be easiest to feed them a steady regulated 4.5v rather than try to step up the .25v. I`ll go by mouser tomorrow and see what they can offer

 

Actually...what do the other two wires on the connector do? Power and ground?

I'm kinda thinking you can just fool it with a properly connected voltage divider.

 

I hear ya. My thing is that if a switch can entirely disable SWAS interference by placing it on Terminal A alone (light blue wire), then wouldn't controlling the voltage on said wire to, say 500mv (nice, middle number to account for voltage/hardware variance) be sufficient? Seems like only 1 wire needs messed with.

I also agree a regulator is the way to go. We just need to know which wires need a regulator (if more than 1), and which wire(s) needs to be in the middle of what voltage range(s) always for SWAS to not interfere.

 

Hmm...I looked at the service manual more there is a steering initialization process the BCM goes through when there is a reset/loss of power. It seems that BCM is looking at a series a pulses depending on the angle and direction the wheel is turned. Any erratic pulses will cause a fault. Someone prove me wrong. lol

 

Ok so SWAS... It is used by a lot of shit. You cannot do anything to disable one system and leave the others fine ELECTRICALLY. It can only be done thru code. SO the SWAS is a multi position sensor that takes it data and brodcasts it on the CAN network when requested. Each system DSC,ABS,TORQUE LIMITING ECT.... when it needs this data it simply looks on the can network. Disableing the SWAS sensor kills the data feed period. This affects all systems. the only way to do this without code is to get a computer and put it between the can network and the SWAS can driver. The can bus triple rings a bell. it could be programmed to feed bogus data to the pid the torque limiting programs used to request Steering Wheel Angle.

After all of this TBH a switch under the Colum cover and a light one the dash for no swas is fine for me. I switch it on when it rains or family is in the car. I would be more interested in a EGR or O2 sim electronics to pass emissions!

 

Se now, there is some info I was looking for. It had just barely crossed my mind that SWAS could also be on the Canbus, in which case it is correct that theres no simple solution other than complete disabling and fault lights.

 

Had my hopes up. But, we're back to exactly what I've done for years: unplugging and just getting so used to the lights being on that you don't even really notice them any more. And for me, the driving improvement is such a night/day difference, I'll always run unplugged.

 

I cut the signal wire and spliced it into a switch that i mounted on the side of the column. I leave it off most of the time, but its nice to leave on when its slippery out or family in the car. Best of both worlds. When you go SWAS off to on, you have to restart the car for it to take effect and make the light go out.

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