Omicron

Hey Tommy, in this thread we've been discussing the TPMS system and how to disable it. Many people have aftermarket wheels and/or winter tires, and it would be nice to not have to put up with the flashing idiot light and beep.

My theory is that there is a TPMS receiver module somewhere in the car, and unplugging it might cause the ECU to stop monitoring and reporting on this function. There must be some way to disable it, as Canadian cars don't have this system or the flashing light/beep.

Can you check into this, and see if Mazda techline (or someone) can tell you how to disable it completely? This is also worthwhile knowing for Mazdaspeed part customers, as I don't think all the MS wheels are TPMS compatible.

Many thanks...

Omicron

Bump?

mdw33333

I'd love to know how to disable the TPMS as well. I have 19" wheels that I'm ready to install, but I'm waiting a bit to see if the system can be disabled. If it can't, I may consider buying new sensors (assuming they will fit my new wheels?)

Omicron

Unfortunately, that cannot be assumed. If you didn't buy them with the TPMS in mind, chances are they won't be compatible.

RosenthalMazda

Correct information sometime takes time. Even if it's not possible, I want the right answer.

Tommy

Omicron

Long as you're working on it, I'm happy. Thanks Tommy.

Omicron

Any luck on this Tommy? Thanks...

RosenthalMazda

No. One of my techs said he would look into it whenever the opportunity presents itself but who knows when that will be. Maybe one of you guys want to play around with your car for a while...?

I have access to wiring diagrams...

Omicron

I'd be willing to look into this Tommy, and have a little already. From what I can tell from the wiring diagram I've seen, it looks like the TPMS control unit is burried all the way under the center of the dash, like behind the stereo. If I'm right, how would you suggest I get to it? I'm loathe to take the whole dash apart...

MazdaManiac

iTrader: (3)

Already tried it.
Unpluging the TPMS module has the same effect as pulling the room fuse - the light goes on and it beeps like you have a low-pressure situation.
That is the case with most of the safety items on the RX-8 - if you remove power from them, they go into the failure mode.

The problem is that it resides on the CAN buss and the PCM polls it from time to time.
If it isn't there, the PCM throws the related system code and sets up the instruments cluster light and beeper.

Omicron

Ok, good to know Jeff. So what would you suggest? How do you think the Canadian cars, which don't have the TPMS, prevent the warning light and beeper?

MazdaManiac

iTrader: (3)

I don't know.
Deleteing the reference in the PCM ROM would probably be a good start.
Anyone know how to do that?

RosenthalMazda

I've sent you a PM referencing your email.

I saw where it is too and it looks like a real pain to get to. We just got shop manuals in...I'll try to take some time to look into it this weekend and to ask my guys at work about it.

The few I have in the service dept that try to work with me on "things" are kind of skiddish about what cars they fool with. Like...a customers car is a nono. Dealing with the sales manager is another thing - taking a car off the lot to "play with" gets a weird look..

We just hired a new general manager - we'll see how he plays out in the next week or so...

RosenthalMazda

That's what my guys have found. They were hoping that unplugging the control unit would not cause a "failure" situation, but all the while expecting it. My main guy was going to kind of ease a Mazda USA tech guy into a conversation about it first chance he got but how do you rush something like that? He was skiddish about the thought for fear of backlash when he really needed a favor. After talking to him, Mazda guys get off the books on a regular basis with at least, some of the techs...Just what I've heard.

It's hard to get info without a willing guinea pig car to study for a couple of weeks (or so)

Omicron

Hmmm. Been thinking about this a fair bit.

So, if the receiver module must be plugged in or the system alarms, then that tells me that it must send an "All is well" signal to the PCM. Most likely when a problem is detected with one of the sensors, it sends a secondary "All is NOT well" signal to the PCM too, or possibly it STOPS sending an all is well signal to the PCM. So, it sounds like I need to determine what voltage is flowing on the wiring with no TPMS faults, then again with a TPMS fault deliberately induced. The delta will be what needs to be dealt with to disable the system. With any luck, one of the wires coming out of the TPMS receiver will be "dead" until the system detects a fault, and when it does, voltage then flows to the PCM indicating a fault - then we could just cut or switch this wire to disable the system.

Alternatively, I understand from one of Canzoomer's posts a while back that there are mini-TPMS receivers in the wheel wells, all of which talk to the main control unit behind the dash. This makes sense, as the TMPS sensors in the wheels themselves must be pretty low power, and transmit via RF to a receiver which must be in close proximity. This being the case, if I knew where exactly the wheel well receivers were, I may be able to figure out how to spoof them into thinking the TPMS transmitter in the wheels are functioning "ok" even if they're not there. It's also possible just unplugging these wheel well receivers will do the trick.

I suspect Mazda's solution to not having TPMS is a fairly simple one, something like a plug with just a jumper or two that replaces the main TPMS control module. Or, as you say, they may just delete the reference in the PCM ROM. Alternatively, this plug may be at each wheel well's receiver, but this isn't as likely as Mazda would not want to include the TPMS modules at all in non-equipped cars to reduce production costs.

So Tommy, can you tell me where these wheel well receivers are located? I'd prefer to start there, rather than disassembling my dash to get at the main control module. Another idea I have is if you know someone at a Canadian Mazda dealership, they may well know exactly where the system is disabled. If they don't know, they could even pose the question to Mazda's tech line that they've got a US spec car that's relocated to Canada, and the owner wants the system disabled. Since this is not against the law in Canada, Mazda may tell them how to do it.

MazdaManiac

iTrader: (3)

There are no wheel well receivers. All TPMS electronics are in the TPMS module.
The signal sent to the PCM isn't voltage, its logic levels so you can't just plug it.
The TPMS receives the OBD-II vehicle speed info on the CAN buss and then looks for sensor info. If any of the sensors don't report (which happens if they are missing or below pressure), the TPMS sends a code down the very same set of CAN buss wires upon which it receives the OBD-II speed info.

Omicron

Ah, ok.

OverLOAD

Maybe investigating in buying a single TPMS sender unit and figuring out how to make it send the same signal when it's not even in the wheel is a start?

Sounds like a lot of trouble for the effort..

Then again, I vaguely remember that the Canadian model RX-8 doens't have a TPMS.. Perhaps a full power cycle (diconcect battery) on the ECU with the TPMS reciever disconnected will re-initialize it's sequence and not poll the TPMS reciever if it doesn't think it's there? or maybe just going without it for a while so the ECU re-learns?

Worth trying..

OverLOAD

Omicron

Yeah, I've thought about both ideas. If I could find the frequency(s) the TPMS broadcasts on, I could probably spoof the signal. But I'd need a frequency scanner for that, which is something I don't have access to right now.

So, I'm looking for the simple solution, based on the fact that the Canadian cars don't have TPMS. I think it's apt to be something simple, and most likely is that the PCM is missing that part of it's programming. But your suggestion of a "master reset" with none of the four TPMS senders present is something certainly worth trying. I'll give it a shot sometime down the road.

In the mean time, I've lost most motivation to do this, as I've pretty much decided to just keep the stock 18" wheels and TPMS sensor, and just put good Ultra High Performance all season tires on them. But I'm still interested in figuring this out, for academic interest if nothing else.

Genom

I've been looking into the cheaters method, where the sensors from the wheels are all put into a small box and presurized. Then put the box someplace out of the way and forget about it :D

I just need to actually pull the sensors out of the wheels now.

RosenthalMazda

This is what my tech was thinking when we were discussing it. Our illustrious general manager didn't think it was a good idea - pulling a perfectly good car off the back 40 to test a theory that, if proven, could sell who-knows-how-many sets of brand spankin' new Mazdaspeed wheels at $500 a pop. :o

<yawn>

Anyway, at least we're not tearing your car apart that's in for service....

No really, we're not. :D

Tommy
-wants to sell more wheels!!

Gord96BRG

One minor problem - the sensors, actually transmitters, are battery powered, right? On others, like Audi's TPMS, the battery for the transmitter shuts down when the wheel is not turning, via some sort of inertial sensor. This is to save battery life, so that the transmitter batteries can last several years. If the transmitters are stuck in a box stationary, the inertial sensors will never turn them on, and you'd still get a TPMS error just like driving on wheels with no transmitters.

I'm not certain that this does apply to the Mazda TPMS, but chances are good that it does...

Regards,
Gordon

Genom

True, but it's pretty trivial to wire up a voltage feed to them and bypass the inertial switch ( I hope) :D

OverLOAD

I know that the manual says that it's shuts off the TPMS's when not driving, but I definately have gotten my TPMS low pressure alarm to go off without moving the RX-8, when I start it up in a cold morning, so I'm not 100% sure that they actually turn completely off.

Still, to bypass them, at the reciever would be the difficult part, since it's almost definately talking on the CAN bus.. or it could be wired directly into the ECU with a dedicated sender unit, but until we see the relevant pages on the workshop manual, I wouldn't even be able to tell for sure.

There could even be a switch or some jumpers in the TPMS reciever box that lets you 'turn it off' in effect, and still be able to go back to the TPMS wheels relatively easily..

OverLOAD

Mr M

First up, I don't recommend disabling TPMS, in fact I think it is a federal requirement when you don't have a spare tire.

Disclaimer aside, the TPMS module is on the CAN, and recognized by the PCM. All functions of the TPMS system however are completely independent of the PCM. Which suggests to me you may just be able to remove the module and install a resistor in the harness to fool the PCM into thinking the module is still there. The trick is fooling the PCM into thinking it is receiving a 'response' from the module when it pings it in the network test. There may already be a resistor in there on non-TPMS vehicles, you would have to look at a vehicle/wiring diagram to confirm this.

If that doesn't work you would probably have to reprogram the PCM with non-TPMS data, but that means going to your dealer and asking lots of awkward questions...If you want to try, go ahead.

Just my ideas...