Introduction: Repair/fake-out Tire Pressure Monitor System

Tire pressure monitoring is mandated on all new cars. These systems are fragile and expensive to repair. After the tire stem broke off on my Toyota Tundra I searched the internet for a economical fix.. I was dismayed to find that the tire stem/TPM part for a Tundra costs more than $96. Moreover, the engine computer must be reset to recognized a new sensor, Several Tundra Owners have reported that Toyota Dealers are ill-prepared to do this and may need to dismount all 5 tires (including the spare) to find at the sensor ID information. The repair, parts and labor, can cost nearly $400.
This instructable describes how a repair can be made for less than $15 (depending on what tools and parts you have on hand.

Step 1: Thread Broken Stem

The sensor and transmitter of the TPM were still good. All that is needed is to repair the broken stem. Reprogramming the engine computer is therefore avoided.
The tire stem of the TPM needs to be threaded. I thought at first that adding outside threads to the unthreaded part of the broken stem would allow me to screw on a new tire stem. I realized after I did this that this approach wouldn't work since the retainer nut needs to fit over the stem. This was a unnecessary sidetrack.
The approach that worked is to tap the inside of the stem and screw in a new threaded tire stem with matching threads.
I had a tap and die set that I bought at Harbor Freight for $8. The best matching tap size was 12/24. The ID of the broken TPM was 0.166".
I cut out the tire stem from an old bicycle tire inner tube. After stripping off the extra rubber, the OD of the unthreaded portion was 0.236". I used my grinder to reduce the diameter of the brass a little bit until the 12/24 die would snugly fit.
I used a little thread locker to make sure the brass part from the tube fit leak-free in the aluminum TPM.
At this point, the assembly could be re-installed in the Tundra wheel.

Step 2: Fake Out Computer

I decided that I wanted to test the repair. Also, I had put a regular tire stem on the wheel with the broken TPM. This wheel could be used as the spare tire where I'm less concerned about monitoring the pressure. Therefore, I was in no hurry to re-mount the TPM. However, I wanted the dashboard light to go out and only report if one of the other 4 tires on the wheels had low pressure.

I needed a way to put the repaired TPM under more than 26 psi air pressure.

I took a short section of 4" ABS pipe and glued a cap on one end and a threaded plug on the other. These parts cost me $15. Any similar closed container that you have on hand would work just fine.

I drilled a 0.4"" hole in the ABS cap and fitted the TPM. After pressuring the pipe to 30 PSI the dash board idiot light went out!! I can carry the tube next to the tire jack.

I'm a little worried that this looks like a pipe bomb if I'm ever stopped by the police. I'm thinking of putting a label on the pipe saying "Tire Pressure Monitor Tester". That should cover it.

All this could be avoided if Toyota made the engine computer open to owners without special electronics.

Comments

author
3366carlos made it! (author)2017-03-03

the guys at sam's replaced only the bad one for 40.00 parts and labor and reprogrammed it without any problems. Awesome.

author
rleyden made it! (author)rleyden2017-03-03

Good to know. I think the cost for replacement has come down quite a bit in the 7 years since my original post. 2 years ago Costco wanted $75 but when I said "OK" they didn't have the right part anyway.
However, my Tundra is now 10 years old and even $40 seems like more than I want to spend.
I appreciate the info, thanks.

author
Hondatek865 made it! (author)2014-04-21

A simpler way to fool the Tire pressure monitor computer, use "Gorilla" tape to adhere the broken sensor to the drop center of the spare wheel. this also works well for all the tires if needed. most small repair shops will not charge much to break down the tire for that purpose, Usually less than the money spent on the pipe pieces. I have used this often without an issue... *note: other brands of duct style tape come loose over time, "Gorilla" brand works best for longevity.*

author
Hondatek865 made it! (author)Hondatek8652014-04-21

P.S.- Vehicle have Tire Pressure Monitor Computers separate from the Engine management computer. However they do communicate through the CAN bus lines as well as transmission, SRS, ABS, and various other computers in most vehicles. Some parts stores and most small repair shops also have the basic TPMS reset/learning tool on hand and do not charge as much as a dealer to relearn new sensors to the vehicle.

author
rleyden made it! (author)2013-10-01

I'm sure if you are able to pressurize the whole sensor it would work fine. You could probably cut off the stem to make your container smaller.
The system still works for me after 5 years. I thought the price would go down with time. Maybe it has. Costco tire center at first quoted $80 to replace the TPMS but then said they didn't have the right part. I had them switch the rim w/o the sensor to the spare so the system works to tell of the rolling tires are low.
I've wondered about someone's suggestion to disassemble and hot-wire it to read high pressure. Perhaps I'd look at that if I need to do this again

author
gravityisweak made it! (author)2013-10-01

I realize this is an older article, but I have the same problem. The threaded part where the cap would go on has fallen apart and the threads are gone. I can't fill it normally or put a cap on it. My question is, will I be able to just pop the entire assembly into a piece of pvc and pressurize that? Or does the assembly need to be pressurized through its own valve stem? Did I ask that in a clear way?

author
turbonut48 made it! (author)2013-01-12

Can you remove all the sensors and mount them on the canister? The you can use sensorless valve stems.

author
Buzzlong949 made it! (author)2012-04-06

Hi, I just wanted folks to know that the tpms sensors in a pressurized PVC tube works great. I put on after market wheels without the sensors and within 20 miles or so the warning light came on and my computer showed 0 psi in all four tires. At least it does for my 2008 Silverado. I put all sensors in a 3" pipe about 8" long with a cap on each end. Drilled a 1/2" hole in the center of one cap and installed a regular valve stem I got at the hardware store . I stuffed the tube with a shop cloth so the sensors weren't able at rattle around. Used plenty of glue so no leaks. Pressurized to ~35 psi and tossed the tube under my back seat and the warning light went out and my computer thinks all four tires are at 35psi.
It does look a bit like a pipe bomb, but it works! Need further help I can b reached at ncbuzz98@aol.com.

author
thebatman made it! (author)2010-12-06

so i work in an auto repair shop
the problem that caused your valve core to shear where it did was incorrect torque when reinserted.
some tech along the way tightened the core way too much. you are supposed to use a 4 inch lb torque wrench because the aluminum stem will break
you should also never use brass cores in TPMS stems as they gall(kinda like weld) to the stem
we dont see a ton of these breaking but we do see a few. one interesting fix we got was one guy had removed all his TPMS sensors and placed them inside the spare tire, aired it up to the right psi and used normal valve stems
also you can get a usb to obd2(car's computer) adapter for about 60 bucks, you can get a really powerful program set and all for about 400 bucks. or you can buy a modus or verus or even pegasus from snapon to the tune of 6-10 k

author
randy82k made it! (author)2010-04-04

Great invention! looks like you can remount it in the tyre now. I think you could also use large PVC pipe. might save money as the large size ABS gets expensive.

author
picbuck made it! (author)2009-10-16

Whoa! Freakin' genius, thanks!

author
stephenniall made it! (author)2009-06-16

cool idea i used to have this software where i plugged a lead into thwe pc and i could see the car Stuff all the hidden stuff and change stuff it was awesome !

author
rleyden made it! (author)rleyden2009-06-16

Software would be the most elegant approach. I didn't pursue it because I had heard that even dealers needed special software even for something as simple as changing a sensor ID. I assumed such software would be expensive and unavailable to consumers. Any idea where I could find the PC based program?

author
Avagio made it! (author)2009-06-04

It's Fugly, but it is genius. Great idea. However this is a premium TPM system many of the systems don't use additional hardware and just use variations from the ABS system to tell when one wheel has a smaller diameter than it used to.

author
Gamer917 made it! (author)2009-03-13

Your car has 5 wheels?

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rleyden made it! (author)rleyden2009-03-13

yes, including the spare. Whether the TPM on the spare is a feature or a liability is debatable.

author
Gamer917 made it! (author)Gamer9172009-03-24

ok

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thearchitect made it! (author)2008-10-21

Interesting. I don't want to encourage you for a disaster, but did you try prying the sensor box open? There must be a simpler way to fool the sensor than carrying a 'pipe bomb' lookalike setting. This sensor thingy sits in the wheel, right? Cheers, K.

author
rleyden made it! (author)rleyden2008-10-21

The sensor is said to be glued shut. I certainly couldn't pry it open easily. Also, the sensor-transmitter is supposed to be highly integrated, so I imagined that it would be difficult to jumper it to sense "pressure high". Finally, I intend to place it back in the wheel eventually, perhaps when the tire needs replacing. I'm more of a computer guy really, so my ideal solution would be to hack the engine computer to, for example, "ignore tire sensor #5". When are they going to add a usb interface?

author
GeekGod made it! (author)GeekGod2008-10-23

Probably never when they can charge $400 for "repair"

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