TPMS

mlines wrote:

Can you send a photo of the TPMS antenna, thanks

Ah, sorry, I forgot that my views on how TPMS works are controversial on this forum.

Please disregard my post above, and see @mlines's posts on this topic.

He states that the TPMS works on either a wheel rotation speed calculation, or on a Doppler effect -- I don't recall which -- though personally I am not clear on how either of these methods would work to correlate wheel position on the single-antenna system in the Jimny.  Perhaps he will explain?

My background: I used standard TPMS components to build a system for a four-wheel equipment trailer I had a few years ago.  But perhaps things have changed in the last decade.  I am always happy to learn something new.

DrRobin wrote:

For my off road wheels with no TPMS fitted I have an Iron Gates SpoofTPMS and placed in the boot in generally works OK until the car gets a bit of mud underneath, then it can get a bit intermittent.

I understand the TPMS module is mounted under the dash on the drivers side, so thought about mounting the Spoof TPMS there to see if it would get a more reliable signal.

Yes, I suspect you are correct in that last statement.  The Spoof box is intended to be mounted near the antenna, which is why the maker specifies the (common) boot location -- but if the Jimny's sensor is under the dash, then that would be the right spot.  We'll see if @mlines clarifies.

Yes the TPMS module is under the dash, on the driver side underneath to the outside of the car

Motacilla wrote:

mlines wrote:

Can you send a photo of the TPMS antenna, thanks

Ah, sorry, I forgot that my views on how TPMS works are controversial on this forum.

Please disregard my post above, and see @mlines's posts on this topic.

He states that the TPMS works on either a wheel rotation speed calculation, or on a Doppler effect -- I don't recall which -- though personally I am not clear on how either of these methods would work to correlate wheel position on the single-antenna system in the Jimny.  Perhaps he will explain?

My background: I used standard TPMS components to build a system for a four-wheel equipment trailer I had a few years ago.  But perhaps things have changed in the last decade.  I am always happy to learn something new.

We left the last discussion on this as "agreeing to disagree"  

And as always I am happy to be proved wrong as that is how I learnt about Jimnys in the first place. So at present I have a viewpoint on how it works and you have a viewpoint on how it works 

Coming from a radio engineering background I am happy with the concept that  doppler effect , g reading or phase measuring lets you identify which wheel the sensor is on when combined with the steering angle measurement. You are correct that the workshop manual  is vague. However I do now have a device that can produce a graph of what it is getting from the sensors so perhaps I will go an record a drive later.

Martin

mlines wrote:

Yes the TPMS module is under the dash, on the driver side underneath to the outside of the car

Thanks.  I thought I remembered seeing it in the usual aft location when the Dinitrol boys had all the cladding off the Jimny, but I must be misremembering.  The TPMS signals are so low-power that the antenna usually must be mounted outside the steel body, but perhaps the Jimny's tiny wheelbase obviates this.  Another vehicle I just thought of that does not use aft mounting is a light commercial-- a proper one I mean, a big van.  I used to run a couple of large vans for my shop.  At ~7m stem to stern, putting the TPMS antenna at the rear would have it too far from the front wheels to reliably pick up the signal, so instead the antenna was mounted underneath the van within the wheelbase.  So if one ever wants to see a TPMS antenna without removing paneling, have a look under your plumber's Sprinter or IVECO: the antenna will be a black box about the size and shape of a cigarette case, mounted on a flimsy standoff.

mlines wrote:

 However I do now have a device that can produce a graph of what it is getting from the sensors so perhaps I will go an record a drive later.

That would be great.  Meantime I will do a data dump of what I (think I) know, as I have a question for the OP.

The TPMS sensors produce a very low-power signal, and do so only at intervals, in typical operation.  This is not least because the battery is just a tiny coin cell -- not enough juice to broadcast strongly or constantly.  But there are other modes besides typical, driving-down-the-road operation.  Here are three ways the TPMS sensors work:

1) Ordinary driving.  The wheels are spinning.  This closes a centrifugal switch, which puts the wheel-mounted sensors into operating mode.  They transmit a small data packet at XX-second (i.e. a double-digit number of seconds) intervals.  The sensors are otherwise silent, though the car is "listening" at all times.

2) The wheels are spinning AND there is a sudden drop in tyre pressure.  This can trigger an out-of-phase broadcast from the wheel sensor-- if your tyre has been pierced, you don't want to wait 30 or 45 or xx seconds until the next normal update.

3) The wheel is not spinning, i.e. car is parked, but the sensor is put into test mode.  This is what your tyre shop uses to check your TPMS sensors.  You will see them hold a device next to each tyre, one by one.  Their handheld scanner sends a wake signal to the sensor, which causes that sensor to send out a data packet as if the wheel were spinning and it is in operating mode.

Now, here is my question to @4x4.  He said in his first post that he was able to read the newly-mounted sensors immediately, before driving the car.  That would imply that the Jimny could send a wake signal like in #3 above, which I didn't think the Jimny could do (some cars can). I tried it on my Jimny ('22 LCV) this morning, with summer wheels just mounted but not yet driven, and could not get the system to display values.  Perhaps I just don't know the correct button inputs.  So @4x4, can you describe how you did that?  I know your Gen3 dashboard is not the same as my Gen4, but maybe it will be a clue for us Gen4 people to pursue.