TPM - Testing a Pulse Width Modulation Generator to turn the Low Tire Pressure Warning Light OFF on a 2010 STi

So. After some digging around... I have come to some conclusion that the TPM module (tire pressure monitor) sends a electric pulse signal to the combination meter (gauge cluster) on the GR STi without having to spend hundreds, if not thousands of dollars. I, your willing test subject, will go forth and defeat this little light of mine... THE LOW TIRE PRESSURE WARNING LIGHT


In the beginning of time, when the tire pressure warning system was federally mandated, all Subaru owners had to deal with the "Low Tire Pressure Warning Light" on their gauge cluster and had no idea how to make this go away. Multiple threads were created by the Subaru community to find a solution to keep the warning light from ever turning on again. Many people brought up ideas such as taping the gauge cluster, creating a "pipe bomb" (pressurized chamber with the tire pressure sensors inside it), leaving the light alone, and even putting air into their tires!

Behold, after years of reading through forums and research, I have found some interesting information regarding the TPM module with the help of the Subaru Manual Gods that may be an ending to our grievances and an answer to all those who have failed to remove the annoying little warning light. And I will try my best to source my findings and products.

And Even though our cars may no longer be made this way by Subaru and their willingness to NOT share any of their wonderful secrets, I figured the world ought to know! And maybe I should've just created a product that I can sell and make profit from all of you other Subaru owners who may no longer care to actually fix this issue any longer.

I wasn't sure whether to post this as a technical or as a journal, but since this could be helpful to basically everyone who has ever looked for a solution and scratched their heads even harder to no avail, I chose to post this here. I am also aware there is a floating free version of Subaru Select Monitor that may or may not be compatible with the good old Tactrix Cable 2.0, but I plan to create a simpler electro/mechanical "fix" rather than tinkering with a software multiple people may have never heard of or used before, nor do they have the supporting items for the software. Besides, the actual software costs money, and the obdII scanner that is supported by the software is also pricey... so who in their right mind would spend this much money for one small little issue that the entire world is supposedly having.


According to the TPM manual, you can use the "Subaru Select Monitor" (a device for checking various things through the OBDII) to check the oscillation from the TPM module to the combination meter (gauge cluster). On page TPM(diag)-25, it goes through troubleshooting the TPM module by checking the voltage and the oscillation of the signal going from the TPM to the combination meter. It must have a 400 ± 20 ms Duty 50% with a high of Battery Voltage and Low of 1.5V.

Little Joey, "What the hell does this mean?"

Me, "well, I'll tell ya, little Joey!"

So, this means the pulse that goes from the module to the gauge cluster must go high to 12 volts (DC) for 200 milliseconds, then go down to at most 1.5 volts (DC) for another 200 milliseconds, and continue this trend the entire time the car is running. Whenever this voltage starts to drop or the pulse starts to change, the light will consider this as either a low tire pressure or malfunction and turn the light on.

I am trying to look into getting a PLM (pulse width modulator) to generator the ever so changing 12v to 1.5v (or zero volts in my case) at the same rate to "fake" my way to make my car think the tire pressure is completely fine. Which in this case, who knows what's really going on! Of course, everything in the car have to also work. Can't just fix one issue while having multiple issues pertaining to it. (i.e. have a trashy gauge cluster that doesn't work and try to get a light to turn ON/OFF).

With a pulse of 200 ms ON and 200 ms OFF, the total frequency comes out to be 2.5 Hz. Given the simple frequency equation of 1/time. (1/0.4 s = 2.5). I will be looking for any PWM that could modulate both voltage and frequency at an affordable cost for all to use one their own time and money.

Once I have my choice of parts, I will continue on my journey to post further into discussion of installation and testing.... whenever that may be or unless one of you guys beat me to it first. --- or maybe one or you have already found the answer and is too GD selfish to share! ---

For reference, see this shared drive content:

for the entire 08 STi manual:

Disclaimer: Just because I wrote a post, doesn't mean I broke your car. Anything YOU do to YOUR car will be the effect of YOUR mistake(s). Just putting this out there since people have been okay with literally suing the crap out of anyone for anything for any ridiculous amount of money.... but if any of you guys who have more experience or education have anything they want to share, I'm all for learning, sharing, and educating.