I would like to put together a compilation of certain electric systems in the Scion Tc. I know this is kind of a mixed thread, but I want to focus mostly on electrical so I thought this would be the best place to post. This would be more of a practical application guide for modifying and/or removing aspects of the car that have to do with these electrical systems, of course for the purpose of going around corners faster. For example:

Airbags. So you want a Sparco steering wheel. The driver airbag, knee airbag and passenger airbag, and if you have side airbags, with brackets, probably weigh almost 100 lbs. As per the factory manual, disconnecting one disables the entire system. You get an airbag light. How is this tied to the ECU, where, and how is it fixable once one airbag is disabled? and light prevention? and speaking of steering wheels, anyone know how to retain the horn on an after market wheel?

Tire pressure monitor. How does it work? Nothing is plugged in. No wires. What happens when you get custom wheels and tires? Does the light stay forever on? Is there a way to disable the system, are there any heavy components to it, and if not, any way to get it to work with custom wheel packages?

Seat Belts. You just got set up with the latest set of Recaros and now you want shoulder harnesses. Those would work best with a roll cage, and in any case you're probably discontinuing use of the stock belt. How do you disconnect the flashing light under the stereo, the light on the dash, and worst of all, that GOd-awful beep beep beeping for 5 minutes to remind you you're an ___. . .

ABS. As my favorite automotive journalist, Peter Egan, penned in the 1980's, "thank God, now here's a technology that finally gives me the ability to steer in to oncoming traffic in an emergency stop situation." We all know it's bogus tech, as no race or true performance car has it. It's a heavy and intrusive set-up in the Tc. It makes noise and it makes me nervous. Want Stop-Techs? Removing the ABS will surely cause the dash-light, how do you disconnect all that properly? How many sensors are on the entire ABS system?

The Black Box. This one creeps me out. How much data is it really gathering? It says in the manual it's only in the event of a crash. If you remove it, what does the car do? This is the one item I'd actually be midly concerned with the legal implications, however I strongly believe that it's ridiculous in that 99% of cars on the road don't have them anyway. How heavy is it? Where is it? And of course, how integral is it to the proper function of the ECU?

This is an enthusiast thread. In other words, keep your whining about legality to yourself. If anyone on here suggests not doing these things because of laws or insurance, I will fight you. Don't even reply. Nobody cares. Hot rodding, "tuning", is not and has never been for pussies. Also, please keep the one sentence "uhh, you can just take the dash lights out" to yourself as well. Everyone knows you can remove the freaking dashlights. that's a last resort, this is to see if it's first possible to do it properly by modifying the entire system.

I look forward to everyone's response, or should I say everyone's ideas for pertinent solutions to the aforementioned. Cheers!

 

Tire pressure monitor - on 07's (I think on 06's too), there's an actual sensor that attached to the inside of the wheel. If you get aftermarket wheels, you must transfer the sensors or you'll get a warning light.

There are no wires because it operates via radio waves.

ABS - There are three types of braking, in order of stopping distance (on a regular, paved surface)

Threshold braking < ABS < Locked tires

Regular people don't know how to threshold brake. They're not racing drivers, so this is expected. So do we just let them slam the pedal and lock the tires, thus not only reducing stopping distance, but disabling steering control? No, of course not!

For the most part, ABS is more about letting you keep steering control - not so much about reducing stopping distance. I'm not sure about you, but I'd rather be able to hit the pedal, steer around an obstacle, and keep going rather than skid right into it.

And no, you can't just remove it. It's tied into the ECU and other systems so deeply it'd be too much work to even try.

 

thanks for the reply paul. I'm thoroughly aware of how ABS works (please re read first post and check my Peter Egan quote), and I'm willing to make the sacrifice for the 1% of the time I may need it for the 99% of the time I trust my own sense in threshold braking. I'd love the guy who works at stop tech's input on this, because that's on my mod list and it'd be a big seller for me if they didn't require an ABS module.

 

^^ i'll make sure erik at stoptecch sees the thread and leaves his input

as for other items on the list i'll try to write as much as i can mentally stand right now (as i'm sorta out of it)

to retain the horn on an aftermarket steering wheel, typically you need to re-route/fabricate and rewire the connections necessary to operate the horn. i do believe weksos has a diy on their forums about general installation for that.

i usually don't play around with the airbag system, so i'll have to look into that.

only the '07+ has the new tire pressure monitoring system which uses mounted sensors inside the wheel, you will need to transfer them into new wheels... otherwise the '06 and below uses the abs system.

seatbelts... (i'll get back to you on that... feeeling too errrrrghhh to think too much)

black box... another magical thingamajig that no one i think really knows about.. and i do believe alot of cars have them.. though probably not usually stated.

and in the event of something.. normally not checked anyway... unless of course, probably what you're worried about. (had a friend overrev because of a stupid downshift and motor went kaboom... they looked into the "box" and found that it revved over 9K or something before it died..... )

[/incoheret babbling]

 

ABS cannot be removed in any efficient manner.

Airbags... the light shouldn't bother you. Obviously you are aware that they are gone. If there were something wrong with them and the light were on, it would bother me, but if they were gone, i'd get over it.

For the seat belt beep, I was surprised to find that there is a pattern you do with the e-brake, pedals, and some other stuff. However, I don't have it on the top of my head. Search for it.

The tire pressure monitors on 05s (maybe 06s?) monitor wheel speed. If the speeds are different by a certain margin, the system is alerted. 07 employs a pressure sensor on the valve stem.

The blackbox is not even worth it. Liability for ANYTHING that happens will instantly go to you if they go to look at the data, and it's not there. Your insurance will drop you, and you'll be paying out the pocket for whatever you cause, for a reduction in what, 25lbs?

Again, if this is a track car, excuse my rude attitude. But if it is not, all I can say is that i'm happy you're on roads hundreds of miles away.

 

First off the air bags have their own control unit, ties in with the ECU, but separate.

The "Black Box" functions are primarily in the air bag 'puter, but some reside in the ECU. Both are flash-type memory and retain their info with no power.

Trung is of course correct that only the '07s and later have actual Tire Pressure Monitor System sensors - earlier models fake it by comparing wheel rotation rates between the wheels using the ABS sensors, and assume any wheel rotating at a different rate for an extended time has a problem.

(While I understand this is "an enthusiast's thread" I'm one of those that believe that made potentially more unsafe to the driver and others on the road [especially when in conflict with legal requirements] should be trailered when on public roads, and used only for those enthusiast pursuits.)

Good luck!

Tom

 

I highly doubt lightning the car and removing some features is going to endanger anyone besides myself. I'm not one of these guys who drives around like an a$$hole, unless I'm on a big freeway by myself I typically drive with 10 mph of the speed limit. I'm a very safe driver. No swerving, tailgaiting, etc. That's bull$h*t. I hope y'all can see why none of these things concern me. . .

As far as the tire pressure monitor, I have an 06, which then would mean disconnecting the abs sensors would also disable the tpm. Someone mentioned an internal wheel sensor and radio transmitter? Is that accurate? I'm skeptical.

The light doesn't bother me, but it's going to bother the state inspector when I go to get my car registered. There's people here in Austin that will inspect and pass ANY car with ANY mods, but there can't be any lights on.

 

Why not figure out why the light is on and fix it? Did you read how to reset it in the manual? Check all pressures, correct them and reset it. If it still comes on you may have another issue. But trying to disable the ABS will be a nightmare, especially to simply turn off that light for inspection.

And to restate the above, yours has no internal sensor in the wheel. And yes, they are typically very accurate. Actually, even the ABS based system is pretty accurate considering mine went off when one tire was 4 lbs lower than the other side.

 

Just a note - the Speedo signal comes from the ABS system, so you may not want to remove that. Turn off ABS light = remove LED. Also, isn't the '07 wheel pressure sensor actually part of the valve stem assembly? Or am I on crack... When I worked on GM vehicles, some factory trucks were getting dealer-installed "large" rims, and they would reflash the PCM with an update for the wheel size, being that it calculated the low pressure from the wheel speed. Probably had something to do with calibrating the speedo as well. Also a freind's new Tundra has a set of aftermarket wheels installed, and the low tire light is on quite a lot. (Believe that's an ABS measuring system too..)

 

the new toyotas have sensors inside the rim itself, that's part of the valve stem.

which indeed is part of the '07+ tCs

 

Sweet. I had the "strap-on" type in my Neon, and 2 of them were destroyed when removing the tires. (1 by me, 1 by a "reputable" shop..) That was nice though, as it displayed individual temperature and tire pressure in PSI as well as warnings. I tried using the reciever for it in the tC, but no-go. Worth a shot.

 

so now we're getting somewhere. turns out the speedo sensor is also for abs? or is the abs sensor for the speedo? I wonder if the sensor would still work for speedo if you took all the other abs $h*t off the car. . .

 

The speedo is driven from the ABS sensors.. The factory manual shows the ABS computer driving the Speedo input, which then sends the signal on to the ECM... The speedo in a typical car takes about 4,000 pulses per mile, but the ABS sensors likely send out many times more than that, so the ABS computer divides it down and sends it to the Speedo... Dunno if the trans. has any provisions for adding a speed sensor.

 

^^ yup.. you beat me to it.. yes.. speedo comes from ABS..

further threads with regarding to ABS removal are shown here:
outlines purposes and issues
https://www.scionlife.com/forums/viewtopic.php?t=116729
outlines steps required
https://www.scionlife.com/forums/viewtopic.php?t=117057

 

riceburner you are my hero. That you can read that diagram, someone should send you a medal. Thanks for the info guys.

I've meanwhile discovered that the seatbelts will just make that beeping. You have to take the lights out and the speaker out, which is fine. That's def on my future mod list, 4 point cage, carbon seats and a 4 point harness. fun! What's great about the Tc's setup is that you can install a cage with the top seatbelt bolt mounts, and the harness belt would bolt directly up to the existing seatbelt mounts. Easy.

So then on airbags. Also did the research and it would be more costly to find someone to dissect and reprogram the ecu than to just remove the damned dash lights. fine by me. I just wanted to see. Whatever it takes. I'm going to weigh every single sensor, bracket, and airbag and post it when I'm done. Ha.

 

man we've got to get that RAAM guy on here and see if he ever got the speedo working again. Now I'm all excited!

 

For seat belt beeping, why not just bypass the seatbelt sensor? Just make it think the seat belt is buckled all the time. Not sure how it's done in the tC, but most cars it's just a switch. Either open circuit or closed circuit = seatbelt on. Sometimes in the buckle, sometimes in the take-up reel.

 

Does the tC have seat belt tensioners like in the xB that have explosive charges to pull them tight in a crash?? They were not that big in the xB hiding in the inter door column.
The ABS probably just takes replacing the master cylinder or just bypassing the system in the hydralics only thought is it may also control front to rear braking pressure and modulate the rear pressure to prevent rear wheel lockup under normal braking as the weight shifts to the front tires. You may also do something about the gas tank emmissions system and lighten that up as well with a blatter tank or fuel cell.

 

...and hit the restroom before you do a fast run - even a can of Pepsi is 3/4 pound. :D

Tom

 

Are you building a track car only or is this a daily driver as well? IMO if you are going to use this car as a daily driver, forget about it. If you're really serious about reducing weight, you can start by taking out everything you don't need. If you're using this as a daily driver, you're going to have to leave stuff in it that is not needed on a track. Kinda pointless.

Here's some good reading for you:

http://crazyjim.ramelot.com/14seconds.htm

Yeah, and that diagram looks pretty complicated to an electrical engineer....