TPMS ( Tire Pressure Monitor System ) Problem

I'm having an issue with my TPMS light on the dash. It keeps coming on after I reset it and I have good air pressure. I drove all the way to hybridfest with this issue. This happened before about a week ago after I installed my PC. This was also just after I topped off the tires to 44,42. I thought maybe I just needed to reset for the "new" air pressure but now after I reset the TPMS it comes right back on after driving for a while.

There are only two things I can think of that may cause this issue. Since the sensors are wireless I think maybe my PC may be emitting some RF interference causing the TPMS receiver to think it has lost a signal. A simple form of unintentional RF jamming.

The other option is that one or more of the sensors are bad. If this is the case I will just have to wait until I get home and get an appointment with my Toyota dealer.

Does anyone know what frequency the TPMS emits?

Anyone have a Scan Tool at hybridfest? I think I read somewhere that the Scan Tool can read all four sensors plus the PSI. Dont know where I seen that. I'm trying to search my shop manual PDFs but my laptop is very very very very sloooooooooooow. Been searching for "TPMS" for about 30 min now Its only a 800mhz PC. I think I might just have to go out to my car PC and do a search on that 2ghz machine.

 

I havnt tried leaving the PC off for a extended period of time yet because thats where my tunes are. I don't like the radio and I don't have any CDs anymore. Since I don't want my PC on for the MPG challenge I think I will just do another reset and see what happens on the 30 mile trip.

I'm sure I hooked everything back up in the dash when I had it apart. Looks like the TPMS ECU is in the dash. If I have time I may just take my dash apart after the MPG challenge if I still have the issue to see if I did miss a connection.

 

That would be hard to determine with out the Scan Tool.

The spare does not have a TPM does it? I'm pretty sure it don't.

I tried resetting the light again and failed to do so. I'm starting to think I may have the connector disconnected or it may have come loose.

I will first hunt down where the connector is and see if its all hooked up correctly. I'm hoping that there is a connector back there where I can easily get to it. If I have time I might try to do that while I'm here at hybridfest. If I don't have time I'll just wait until I get home and while I'm at it I will try to give the EV light another try by creating a simulated circuit.

 

Well after another reset it takes a good ~30 miles before the light comes back on. I made an appointment with my local dealer. I have unplugged my PC today so there wont be a chance for interference when they test it tomorrow.

This is going to run me somewhere between $30 and $100 depending how long they take. I'm going to tell them all I really need is to confirm the scan tool can read the four sensors and their pressure. If it can do that then I know my PC is causing the interference. If thats the case I will just see if they can disable the TPMS. I don't really need it because I check my pressure often enough that the TPMS is basically useless to me.

 

Well if it cant be disabled or tricked into staying off some how I guess I can give unplugging a try. If that don't work I can always disable the idiot light by desoldering a few things and adding a switch in case I need to enable it again. If I have to go that far I would also try to enable the EV light again while I'm back there.

 

OK I'm back from my dealer and I still don't know whats causing my problem.

First I had to fix their Techstream computer because someone flipped the screen resolution so the screen was in the vertical position instead of the regular horizontal and no one knew how to flip it back. This is a simple proble for me to fix because it happens every once in a while where I work.

Next we tried reading the transmitters in the tires. We was able to read all of them just fine. I was amazed with the program they used. It read the PSI with in .1psi. Its pretty cool. It also had the pressures that tripped the TPMS light. Everything there said it would trip when pressure dropped %20 from my current pressure.

Then I tried turning on my PC with both bluetooth and wifi enabled. The Techstream computer was still able to read all the pressures in real time.

So now I'm left with Wth. We went over a few ideas and one of the things I'm going to try is lowering my tire pressure back down to the low 40s to high 30s for a while. Another idea is that maybe going over bumps in the road might cause it to trip the TPMS.

I will continue to diagnose the issue and post results when and if I get them.


I really want a Techstream or heck even the ScanTool. <_< Will someone buy me one?

 

Well after about 200 miles the light has not come back on. I have not even changed the tire pressure yet. I think I will ride this one out and if I get the light again I will drop the pressure and do some further diagnostics. I guess I just needed to take the car to the dealer and scare it a little.

On a side note I really think Toyota should include the tire pressure on the MFD some where. The Techstream computer was able to show all 4 plus room for a 5th sensor with psi readings like 40.3psi. What would be interesting is if the Prius can really handle a 5th sensor in the spare tire. I should have asked the tech while I was there.

 

Here is a quick update.

I never did drop my pressure down to see if that would fix the problem. I have yet to see the light again. Nothing has changed since I took it into the dealer.

 

Here is a quick update.

I never did drop my pressure down to see if that would fix the problem. I have yet to see the light again. Nothing has changed since I took it into the dealer.