I have been checking this forum to see if anyone has ever mentioned any of the unique issues with the spare tire on 4.3 Rav4. This thread seemed like a good spot because it has a few other things that need some clarification.
The most interesting point I have learned is that Toyota (according to a well informed "factory man" who covers quite a few dealerships) has noted an unusually high failure rate of the sensor units in the spare tires! It is his opinion that the failure rate of the spare tire sensors (barring instances of tire-iron/TPS interaction) is twice that of the sensors in the other four (rolling) wheels. The reason he has surmised is "slamming the door".
I do not work for Toyota, nor Pacific International (the folks who make the sensors), but I have turned a wrench for over forty years…and I do know a few Toyota factory techs and lots of dealership-wrenches. For the most part, they share this opinion. After thinking about his premise, it does make sense; the sensors in the wheels are all the same…all made by Pacific, the same model, and in most cases mounted in the same model wheel. The only difference is that the shocks and jolts incurred by the rolling wheels are vertical, but the stresses incurred by the spare tire are horizontal (as in "SLAMMMM"!).
The other point that seems to need clarification is how the TPMS warning light works and what the different displays mean. When the light simply comes on and stays on, this denotes one of the five tires (yes…the TPMS ECU receiver, located in the right-side cargo compartment fender well, looks at all five tires) has transmitted a pressure below the preset alarm pressure (in this case around 26 psi) the light will turn on. It is the "BLINKING" light that is the troublesome issue. If, in fact, the TPMS warning light blinks for thirty-seconds and then stays lit, the problem is a TPMS system failure. The nature of the failure can be with any component of the TPMS system: an ECU problem, a receiver problem, or (the most likely) a transmitter problem.
In the case of the last Rav4 I worked on (2007) the owner was upset because the tire dealer repeatedly reset the TPMS light, only to have it come on again after approximately 25-minutes driving time. After noting the TPMS warning light come on at KOEO, but blink for thirty seconds and then staying on, I knew that it was a "system failure" of some sort. Yes…"system failure" sounds ominous, but it is the term Toyota (and Motor and Alldata) uses in the service manuals. At any rate, I first went from tire to tire with my Ateq VT30 monitor tool. When I got to the spare tire, there was no response…the sensor was dead. After replacing the sensor I found that the old one had a crack in the plastic where the metal valve stem meets sensor body. The rest of the repair required scanning all of the sensor ID's into the monitor and downloading them to my PC…and then registering the new spare tire's ID (and the location of each ID) into the Rav's ECU. The light issue was resolved.
Hope this explains the TPMS troubleshooting procedure and the spare tire issue.