I had the rear pair of tires of my 2006 Toyota Prius changed recently. Both were already bald and one was also leaky. The Tire Pressure Measure Sensors were pointing correctly that the leaky tire would lose pressure after about 5 days it was filled and the light would disappear after the tire was filled with the correct pressure.

I decided to change both rear tires since they actually needed to be replaced anyway, instead of fixing only the leaky tire. Just after the tires were replaced the tire shop owner asked me if the TPMS light was on all the time before I brought the car to him and I told him that this would happen only when the tire had a low pressure. He showed me using a device that apparently reads the TPMS sensors that both rear TPMS sensors had low battery and needed to be replaced for $50 each. I said that I would not replace since they were working fine all this time and hoped that this was only due to the change and the light would go out after a few days, but it keeps on all the times, sometimes even blinking.

I think that it is really a big coincidence that only the TPMS sensors on the new tires failed exactly on the day the tires were replaced. Is that normal the TPMS sensors fail upon tire change or I just happened to run into a very unlikely situation? Could the TPMS sensors had been replaced by nonfunctional ones by the tire shop to try to sell me new ones? He didn't allow me to see the car being serviced (even when I asked so), so that made me suspicious.

  • Did you actually resolve this issue? Reading both answers and your comments, it looks like the issue is still on. – Jenny O'Reilly Jan 6 '18 at 11:38
  • @JennyO'Reilly Not, I sold the car like that. – Gabriel Diego Jan 6 '18 at 11:46
  • Thanks for letting me know. That's a "solution", I didn't think about. :-) I was just curious, because I had a similar problem recently. – Jenny O'Reilly Jan 6 '18 at 16:27
  • @JennyO'Reilly The solution is to replace them. The main question here was why they stopped working two at same time after the tires were replaced. I thought this was very shady. – Gabriel Diego Jan 6 '18 at 16:50

Sounds like an indirect TPMS. These can be easily damaged by tire-mounting machines. If one or both are damaged, you can get dash light staying on. If they're not damaged, sometimes they just need a reset, especially if you don't change all tires at once. Indirect sytems test revolutions, not pressure. So it will sense a problem if 2 front tires have more wear than 2 new back tires. Reset procedures vary, sometimes you need a scan tool. You have be sure all 4 tires have the correct pressure before resetting for wear. If you have a driver display interface, sometimes they can be reset from the menu. Like Fred Wilson said, the batteries do wear out after 10 years, +/-. But, like you, I also think that's way too coincidental. I'd get a second opinion to make sure they're not damaged, check all pressures and see if they can be reset. Indirect TPMS will be on valve stems or attached to a wheel's drop center. Good luck!

Edit for your questions in the comment section. It wouldn't let me put this as just a comment so I had to edit my answer instead. Let me ask a couple of questions. Can you confirm if it's an indirect sytem for me? When you say it flashes sometimes, how so? Does it flash like 3 times and go solid again? How often? Does the ABS light come on? When they showed you the device, how do you actually know the fault was low batteries? What did it say or look like specifically? Also, some models have a reset button under steering column where your knees are. Look to see- do you have a reset button? If so, don't touch it yet, just let me know. Did you check the tire pressure on all 4 wheels yourself to make sure they're correct? It's possible you can use an OBD2 code reader to erase faults but, if you could, I'd like to know what the fault codes are if you do use it. It should connect to the instrument panel. A light on your dash can be from some type of damage and will give a code. Sometimes a relearn process needs to be done by the service technician after servicing your tires. If it's not done or done incorrectly that could also cause a fault.

Edit for additional comment questions: Is your reader wireless as well? More details on how you did your reset- something like, held it in for 3 or 4 seconds and the tpms light blinked? Is that about right? How long did it blink for, how many times, how quickly? The lowbat indicator you spoke of: that was from the serviceman's wireless tpms tool, right? He came to the front to show you this AFTER the work was done? Odd that he wouldn't scan each sensor FIRST to get info on them, including preexisting faults and to get their custom ID's so they know how the ECU recognizes them. Can you give me a little more detail about when your tpms light blinks? Only on startup? While driving anytime at all? If so, what details can you give me about that? If your OBD2 reader is wireless, you should be able to verify codes for low batteries or anything else yourself. Have you? Lastly, the ECU stores where each sensor is for each tire. It may be worth a try swapping the back two tires, filling them to spec and redoing the reset (just in case they swapped those two wheels by accident when they were doing the work). On a side note, those trouble codes you did mention- P0420 and P0116 together indicate you should check your coolant temp sonsor with a multimeter to see if it's bad or check your thermostat.

Updated edit: Most direct systems have some way of knowing what tire's sensor it's reading from. Sometimes it's by unique SN's or ID's, sometimes it's specially placed antennae that detect directional rotation; but, the point is, the two back sensors could have been mixed up. Which would be fine if a resynchronization is done (recalibrating the transponders). What you did with the reset button was reset the tire pressure baseline. I heard at some point that some models need a wireless tool to resync with Toyota models. If you did the pressure reset correctly- Hold the button with the ignition on (not car on) until the tpms light blink 3 times, then leave ignition on for a few minutes before shutting it off- then it sounds like you did it right. Since that didn't work, I would try swapping the two back tires to see if ID's were out of place. Lastly, bring your car into a different tire service place to explain the situation. Ask if they can try resynchronization first, since you suspect it may not have been done. Then ask if they can get any trouble codes to verify low battery on BOTH sensors. Maybe they'd be willing to look and make sure nothing was damaged like an antenna or seal... Finally, if none of that works out and their codes match low batteries, 'I guess' that's it but would be very coincidental for even just one to suddenly have become just low enough at the time of servicing one tire, let alone both!

Regarding the other codes- the ECS can be tested with a multimeter. An auto part store should have spec values for that or your manual. If your thermostat is stuck open, you'll feel coolant running through the upper radiator hose upon initial startup (it shouldn't open until it warms up a bit so you shouldn't feel fluid running yet). It'll also take longer than normal for your heat to start working and your engine to warm up. If it's stuck closed, your engine will run hotter than normal and overheat. Those two codes you got could also just be from letting your coolant level get too low at some point. Clear them out and keep an eye on your engine temp. If you get any warning signs then you can see if you get those codes again. If so, one of them is probably defective. Sorry I couldn't be more help. Good luck.


  • I have a OBD2 code reader. Can I use it to reset the tire pressure readers? I'm afraid that they where damaged, but still it puzzles me that the TPMS reader showed low battery at the tire shop. It would expect that a damaged TPMS would give no reading at all. I will refill the tires tomorrow and erase the troble codes to see what happens. – Gabriel Diego Jan 16 '16 at 7:59
  • Edited answer to address this comment. Please read answer again and comment back with answer if you don't mind. Thanks. – Mustangguy809 Jan 16 '16 at 10:34
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    I've tried some things over the weekend (refill the tires, reset the sensors...) to no avail. It is a direct system, with the sensors inside the tires. It flashes several times, more than 10 for sure when the car is started. ABS light is off. The device was reading something like LOW-BAT or so. I saw the reset button and did the reset as in the manual, but it didn't change anything. Yes, I even inflated a bit more than specified as usual to save more on gas (I'm getting almost 60 MPG already). The OBD2 reader reads other problems that the car has (P0420 and P0116), no tire related codes. – Gabriel Diego Jan 19 '16 at 4:48
  • Reread my answer for updated responses and questions. Also, to reiterate here, swap the back 2 tires and redo your reset process. Let me know how that goes. – Mustangguy809 Jan 20 '16 at 2:17
  • I don't have a TPMS wireless reader, only a simple OBD2 scanner. The reader I mention belongs to the tire shop I replaced the tires. He only showed it to me after the work was done. The TPMS light blinks only when I start the car for some 10-20 times then becomes solid until the car is switched off. I have my doubts that swapping the wheels would influence anything, does the sensors have a specified position? I thought they would be seen as being the same. How can I check if the temp sensor and the thermostat is bad? – Gabriel Diego Jan 21 '16 at 1:01

If I read your question correctly the sensors have not completely failed yet. The device that read the sensors is showing that the batteries in the sensors are getting low. These batteries are small, the size of watch batteries. An inertial switch wakes up the sensors when the tire begins to roll. They are expected to last 6 to 10 years in normal use. So at 10 years old in your 2006 vehicle it is not surprising that they are low on battery power. They will likely continue to work for a limited time.

The tires have to removed to change the sensors. Incurring more labor time. An offer to change them at the same time as the tires it would decrease overall cost. It has become common practice to check them before the tires are changed. Failure to do can result in angry customers when a TPMS sensor failure does occur shortly after tires are changed.

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    The tire shop owner used what I assume to be a TPMS reader and it read low battery. Still this annoys me since the tire light now is always on and flashes sometimes. I was even more annoyed that he just suggested me to change it after the tire change was done, which indeed increases the labor. – Gabriel Diego Jan 16 '16 at 7:53

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