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.