Tyre Pressure Sensors - The Bit You Don't See

[Gerg]

I have inherited a tyre pressure sensor off a 2015 Auris.

For all those who wondered what one looks like off of the wheel, here are some photos.

I think the pressure is measured up the small hole to the left in the first picture.

The air enters the tyre through the vaguely triangular aperture.

Once the button cell Battery has gone flat, then the whole unit gets swapped out.  (5+ years?)

 

[Ashfaq]

Thanks Greg. Did see these while tyres were being changed. Held my breath as these cost more than the tyres. Luckily no mishap.

Thanks and regards.

[qettyz]

Sensors cost like 25£ / pc. The programming is expensive if done at dealer(5min job with correct tool).

[furtula]

Would be cheaper just to have a car towed and tire replaced, than to bother with these things, from what i read on the forum so far, it's just problems.

Seeing as some manufacturers are trying to force cameras instead of rear view mirrors, but you still have to look towards the place where the old mirror was, i'm starting to look at older cars  who were more mechanic with nostalgy.  

If i was not in a rust prone area, i'd be holding on to something from mid to late 90's when cars still looked good, had performance to match, but without the ton of electronics put in todays cars.

[tuskar]

I understand if one unit goes after five years its best replace all 4 plus programming probably 200 . Anyone know how to disable this successfully ?

 

[Heidfirst]

the Battery life is typically 5-6 years hence if 1 goes the others probably wont last much longer. iirc the Toyota oem sensors are listed at £180 each at a dealer ...

A working TPMS system is part of the MOT for all cars first registered new after November 2014.

[Steve Whits]

Can't really tell from the picture, aren't the batteries replaceable

[furtula]

Looks like it's all covered in some sort of moisture barrier, either like hot glue, or more probably, some varnish (i saw varnish being used on power steering module).

In my case i was able to remove the varnish by scraping to unsolder a part (soldering iron also helped remove it). 

In theory it should be possible to remove it given enough patience, maybe a varnish remover, the whole thing should be resealed the same way.

Seeing how it's priced rather hefty, maybe @Gerg would be willing to give it a shot trying to get the Battery out, since he has no need for a working sensor anymore.

 

[Mooly]

I wonder if removing/replacing the Battery causes the unit to lose any custom programming i.e would  the car still recognise and talk to the sensor. 

[Steve Whits]

It appears they have a lifespan of between 5 and 10 years depending on driving style.  A lot of stop start driving wears the Battery out quicker than driving at steady speed.  It also appears they're in a molded housing so batteries aren't replaceable.

[furtula]

Where there's a will, there's a way...

I found this video for Lexus, showing that batteries can be replaced with a bit of poking around, and the error alert about pressure disappeared after new Battery was fitted, so the programming probably says in there permanently.

https://www.youtube.com/watch?v=4F6sBRfEwzw

Anyway seeing that when the Battery is dead, they will probably just throw it away, i'd rather attempt to get it replaced, then just throw money at a dealer, you can't really lose either way.

[Steve Whits]

How do you find out which one has failed?  

[furtula]

9 minutes ago, Steve Whits said:

How do you find out which one has failed?  

Techstream can show you the location of the problematic sensor, and should be able to register a new one, at least according to this very detailed manual http://blog.uobdii.com/toyota-techstream-replace-broken-tpms-sensor-with-new-one/

[qettyz]

I could not get Techstream to work programming TPMS codes to the ECU. Tried two different mini vci cables.

Seems that these chinese cables do not support protocols to write ECU etc.

I bought Autel TS501 tpms programmer. I can program sensors, read invidual sensors, check Battery state, re-learn ecu wih new codes.

Worked nicely for my 2014 Auris. Also works with my friend Auris.

Price for that tool ~200€. Not bad if friends can share it.

[qettyz]

Also, Techstream does not show location of the sensors. Only list of them. @furtula 's link they have picture of the car and showing locations, dunno wheres that from. Not from Techstream.

Edit: well if you play around with tire pressures with Techstream, you learn which tire has what sensor.

[Gerg]

8 hours ago, furtula said:

Seeing how it's priced rather hefty, maybe @Gerg would be willing to give it a shot trying to get the battery out, since he has no need for a working sensor anymore.

On the sensor I've got the batteries sit in a space filled with potting compound, which I've always taken to be an epoxy-type of filler (Can you confirm, Mooly?).  It's certainly *very* tough.  The Battery itself looks to have spot-welded connections.  I think that removing the epoxy-like stuff would involve plenty of heat, so far from ideal.  Also, soldering attachments onto the button cell can sometimes cause them to overheat and burst open. 

I imagine that their priority at the factory was trying to make the unit completely waterproof and damage resistant.

[Mooly]

Hard to say without seeing one but the image looks as though it could be some form of 'potting compound' specifically for electronic use. These have to be chemically stable and not release any kind of acidic contamination... like most types of silicone bath sealant do.

A jewellers screwdriver and a bit of persuasion might be able to crack it all free.

Potting Compounds

Scotch Weld

 

 

 

[furtula]

15 hours ago, Gerg said:

 The battery itself looks to have spot-welded connections.  I think that removing the epoxy-like stuff would involve plenty of heat, so far from ideal. 

You can buy batteries online with spot welded connections, so you just solder the other end to the PCB, so that's not so problematic.

Getting the device out safely is the trickiest part.

[Saxmaniac]

Have you looked at pattern sensors? They are available apparently for most makes but no idea whether Toyota can be programmed to recognise them. eBay has them listed from £50 for a set of 4 or Schrader branded for £36 each oem quality. However, when the time comes I will certainly try to do a repair so please keep us updated how you get on!

[mrpj]

If the tyre has to be dimounted from the wheel to remove the internal sensor, it might well be easier to just have the sensor replaced? All the hassle of buying batteries, accessing the Battery with the risk of damaging the sensor assembly, fit new Battery, reassemble sensor then mount tyre and find out you broke something!

I'm sure most decent independent garages have the required equipment to detect which sensor has failed (if necessary) and or reprogramme a new one/set.

Thank goodness I don't have them and use a gauge to regularly check pressures rather than rely on gimmicks.

[Saxmaniac]

8 minutes ago, mrpj said:

If the tyre has to be dimounted from the wheel to remove the internal sensor, it might well be easier to just have the sensor replaced? All the hassle of buying batteries, accessing the battery with the risk of damaging the sensor assembly, fit new battery, reassemble sensor then mount tyre and find out you broke something!

I'm sure most decent independent garages have the required equipment to detect which sensor has failed (if necessary) and or reprogramme a new one/set.

Thank goodness I don't have them and use a gauge to regularly check pressures rather than rely on gimmicks.

Such is the nanny state we live in 

[Mick F]

On 6/25/2019 at 9:10 PM, Heidfirst said:

A working TPMS system is part of the MOT for all cars first registered new after November 2014.

Does a warning light come on when one of the batteries is flat?  If not, how would the MOT tester know anything?

Mick.

[FROSTYBALLS]

51 minutes ago, mrpj said:

Thank goodness I don't have them and use a gauge to regularly check pressures rather than rely on gimmicks.

TPMS is intended to warn of one or more tyres being significantly under inflated, which could affect the safety of the vehicle. Not intended to replace regular checking of tyre pressures.

[Heidfirst]

4 hours ago, Mick F said:

Does a warning light come on when one of the batteries is flat?  If not, how would the MOT tester know anything?

It should as it won't be receiving a signal from 1. When I fit my winter wheels/tyres with no TPMS valves the warning light comes on.

[qettyz]

Toyota ECU's can learn 4(-2014) or 8(2015->) TPMS sensor codes.(There is model differences)

On 8 sensor model you can change tire set with TPMS button.

When ever car does not find coded TPMS codes wirelessly it will be shown as first blinking light and after that steady on-light. So yes flat Battery triggers also TPMS light.

On 4 or 8 sensor model car you then have to re-learn ECU if any of the sensors is changed. Exeption:you can buy sensors what allow you to program them to same as sensor whats taken away, then ECU doesnt know. But then, if you buy programing tool, then you can also re-learn ECU.

I am quite sure that there is many sellers at eBay who can pre program sensor for buyer. That would be reasonable cheap way to replace sensor. Sensor code is written to the sensor, to buyer can tell it to the seller.

Currently there is no way to disable TPMS function on newer Toyotas. Priuschat had howto manual to disable tpms on older Gen2 prius. It was done with jumper wire on TPMS ECU. They have not had success with 3rd gen Prius.