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Discussion Starter · #1 ·
I finally took my car to a garage that can read the current TPMS valves and program a set of new sensors.
I took my set of Toyota wheels with winters from when I had my old RAV4.
He read the code from each wheel which was a different code for each wheel. I believe the cars computer has been programmed with these 4 codes.
Mr T said they would add 4 different valves to the other set and then charge me a fortune to add these extra 4 codes to the cars system so the two sets can be exchanged. Good idea but not at £360 inc valves.

He programmed the new sensor, placed it in the RAV4 wheel and put that wheel on the car as he took the other off. He then did the other three.
Everything seems fine.
This was a very experienced chap but wasn't sure about some things:

I said I might now put one of the wheels currently off the car in the boot as a spare after buying some block polystyrene and making my own boot innards - 8.5 inches deep.
He said he thought the spare would be better without a TPMS valve as you don't know which wheel will go flat and then you would have 2 on the car with the same code. Would the car then realise that one code had gone missing and not receiving it - fair point.

Then we discussed what would happen if I put one of them in the boot which meant there were then two identical signals being transmitted - possibly two slightly different pressure readings. He wasn't sure how the cars computer would react if the wheel in use with the same signal went down but the one in the boot was still saying 33lb. Would the light come on or not? One second it was saying 25lb and the next it was 33lb.
We even joked about wrapping the spare in aluminium foil to block that signal but when a flat occurred it still needed to be put on the car and the chances are 1:4 that it is the same wheel code as one of the other three that are still OK.

Anyway, my winter wheels are now on but what should be a very simple idea of putting one of the originals in the boot is leaving me and an old mechanic a little confused.

Oh for the old days when I just checked the pressure once every few weeks and did a visual check when I walked up to the car. 35 years without a problem and then all these new gadgets come along.

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Each sensor has a unique code which is programmed into the car system via the Techstream software. Its possible to have more than 4 sensors programmed to allow for winter tyres (and apparently the spare).

According to the handbook:

When a tire is replaced with a spare tire (vehicles with spare tire)
Vehicles with full-size spare tire: The spare tire is also equipped with a tire pressure warning valve and transmitter. The tire pressure warning light will turn on if the tire inflation pressure of the spare tire is low. If a tire goes flat, the tire pressure warning light will not turn off even though the flat tire has been replaced with the spare tire. Replace the spare tire with the repaired tire and adjust the tire inflation pressure. The tire pressure warning light will go off after a few minutes.

Looks like the system can monitor all 5 tyres simultaneously.
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