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TPMS (Tire Pressure Monitoring System) Schematic and Disable Attempt
Dear Friends,
You may by now be painfully aware of the fact that the "smart" tire valves with wireless sensors that communicate with the on-board CPU, ALL contain a battery that will die a certain death within about four years. Furthermore, the death of each tire transmitter inside each wheel, will not be coordinated with the other 3 wheels. This fact will eventually force you to pay for un-mounting the given tire, buying a new valve pressure sensor, having it installed, and then re-programming it to the master CPU. This you will have to do 4 separate times.The last step can generally be performed only by the Lexus Dealer! My dealer charges ~$260 per wheel (new sensor and labor). That amounts to a total guaranteed expense of $1040! All for $2 worth of dead batteries (which mysteriously can not be replaced)! This to me seems like either: a very crappy design, or simple extortion. Thus, IMHO it is our duty to help Lexus fix either of these problems. To that end, here is my attempt to "turn off" the TPMS system and the associated accolade of blazing warning lights on my dashboard! I was unsuccessful. However, I may provide enough information here to allow one of you to build on my work, and help the rest of us succeed:
First, the Full schematic for the for 2006 GS300 and GS430 system is (attached). The image below is partial:
Partial TPMS schematic. Full schematic is attached as *.pdf.
Secondly, I had to find the TPMS module. It is immediately above the Navigation unit. See next 2 photos:
Nav unit removed...
TPMS (Tire Pressure Monitoring System) is the small black module on top)
Close up of TPMS:
The modifications that you see to the wiring in the background were made previously for the VAIS audio mod, and the Phone-keypad/DVD bypass mods - shown in other threads on this forum.
Close up...
Now, I had to determine the voltages and signals at different wires going to and from the module. Thus metering the pins by pulling the connector was absolutely useless, since the connector is UNPLUGGED from the module:
Metering the pins to an unplugged connector...
Not very useful since the module uses two way communications.
Here, I must state that I did find on the web one forum where a gentleman attempted this mod, and recommended grounding the blue wire shown in the schematic as pin 9 (RDA). Doing so on this model DID NOT WORK. As you will shortly see below, I rewired the unit to allow either Grounding or raising ANY pin to a given voltage, or to Open any set of connections while the circuit is still operational and see the signals under any of those conditions from both sides (the TPMS module side, the Receiver side (upper block) and the main CPU side. Summary of measured voltages under various conditions (short or open) will be discussed below.
All wires to the module are cut and jumpered. This allows to measure the voltages at either end, but not (easily) while connected!
So, to allow the ability to measure all the connections while any wire is open or shorted, and while the module is simultaneously connected, I built this matrix board:
All pins are shorted horizontally only - as the photo is shown.
In the above image, all ROWS are shorted horizontally (only) as the photo is shown. The Red, White and Blue jumpers allow the ability open the connection and measure the open circuit voltage at either the Module end, the Receiver End, or the CPU end. OR using the row of black pins to the left of the jumpers, I could measure all voltages while the signals are active/live and connected.
For the bravest of the crowd, it is possible to remove the TPMS module from its can, but soldering the hybrid circuitry without the available schematic was a bit too much for me to swallow:
Module removed from its protective can. I do not recommend doing this unless you can ensure proper grounding and static protection techniques.
InSummery, what I have found is as follows:
1. To address the only available post on the web that recommended shorting the blue pin 9 wire (see attached PDF schematic of entire TPMS):
When the blue wire between pins 9 and 1 is OPEN, The Zener diode at pin 1 (RDA) is at +3.5V. The RDA voltage at pin 9 is +10.8V. When the wire is in standard operational mode (shorted) the voltage at that point (between pins 9 and 1) is +3.3V. Shorting that pin to ground will force both the Zener and the module to dump all possible current to Ground, possibly burning-out the zener eventually. In any case, when I did this, the warning lights on the dash did not go away.
2. Then I decided to cut the power to the entire receiver module, by "opening" the red wire at pin 10 going to pin 5 of the receiver module. This is a +5V supply from the TPMS to the receiver. The TPMS module recognizes that the receiver is dead and sends the error signal to the main CPU. Opening the pink Ground at pin 4 together with pins 10 and 9 was also useless with the same error signal.
3. Then I decided to cut all communications from the TPMS module to the main CPU. There are only 2 wires doing this: the LG (light green) and GR (Gray) wires. Both carry a DIGITAL ("AC" type) signal BIDIRECTIONALLY to and from the CPU. The voltage here fluctuates at very high speed from 0 to +3.5V. Without a signal/spectrum analyzer I had no way of determining the actual language manner involved. In any case, I tried Shorting them to Ground, together or separately. I tried shorting each side or pair - together and/or separately. I tried pulling them up to +3.5V together or separately. I did all this in combination with disabling and enabling the Receiver module. ALL to no AVAIL - the error signals were always flashing; some sooner, some later, but the bidirectional nature of communications with the CPU ensured that EITHER the error code was generated by the CPU or by the TPMS module!
4. I also focused on the Yellow RESET wire (Pin 2 of the TPMS) which allows you to set the minimal error threshold for your tire pressure. Thus if you want to see lights flashing at you when the tire pressure drops below say, 28 psi, then set your ALL your tires to 28psi and then press and hold this button (just above driver's left foot) for 3 seconds. This will set the low-end reference on your vehicle. Don't forget to pump the tire pressure back UP when finished. In any case, the output on this pin (pin 2) is +10.8V from the TPMS module out. Shorting this pin in combinations with ALL of the above did not yield any valid results of shutting down my Christmas Tree Dashboard!
Thus, humbly defeated , I leave this legacy to the one night in shining armor who can wield this sword from the stone.
Last edited by joe_gunn; 11-01-15 at 03:13 PM.
Reason: First Post stripped the attached full TPMS schematic...
have you considered the replacements from EZ sensor, if I recall, rockauto.com sells them for around ^$40 a piece and my nearby Americas tire installed them for $80 a set. If I recall, They also offered the sensors for 70 a piece and probably would do a package deal. Lots of trouble you are going through to save around 300 bucks
I had all four replaced YESTERDAY at America's Tire (old Discount Tire) in SoCal for $255 out the door. Not factory obviously, but their brand with a 2 year warranty.
I did try several shops like TireRack and others. However, most shops told me they could not do the proper re-programming of the new sensors to the main CPU, and thus turn off the blazing dash board.
In any case, I am less distraught about paying the the dealer (after all I can afford the Lexus and the burdens that come with it). My main beef with this design is the fact that no-one is giving us (the Lexus community) any worthy solutions to the problem. It seems to me that the system keeps shearing and fleecing us - and I just don't like to be fleeced!
P.S. Attempting to attach the *.pdf of the Full TPMS system; the first post seems to have stripped it.
There is a solution to the problem. Buy new sensors and have them installed. I found three shops that said they could do it within 5 miles of my house. Turning off the lights without fixing the issue is not a solution.
There is a solution to the problem. Buy new sensors and have them installed. I found three shops that said they could do it within 5 miles of my house. Turning off the lights without fixing the issue is not a solution.
Some of us don't care for the TPMS light and function. I can figure out that my tire is low by the way the car drives/handles.
You can purchase TPMS sensors for $60 each and have the computer reprogrammed by a tire shop. The sensors are rated for 7-10 yrs of Service life, so an 06-08 car owner should prepare to tackle TPMS failures.
Hey man, nice job/try! It looks like you put some significant effort into trying to figure this out. Many have issues with the TPMS (myself included) and I wish you luck in your endeavor.
We applaud the effort but its roughly $65 to get a TPMS replaced at Americas Tire
On a side note-
If a tire shop cannot read your sensors with their handheld box. Have them go to year 2006 in the unit.
The shop finally was able to read the sensors in my rims when the tech entered vehicle info for a 2006 Tacoma
10-27-15, 10:21 PM
TPMS (Tire Pressure Monitoring System) Schematic and Disable Attempt
! All for $2 worth of dead batteries (which mysteriously can not be replaced)! This to me seems like either: a very crappy design, or simple extortion. Thus, IMHO it is our duty to help Lexus fix either of these problems. To that end, here is my attempt to "turn off" the TPMS system and the associated accolade of blazing warning lights on my dashboard! I was unsuccessful. However, I may provide enough information here to allow one of you to build on my work, and help the rest of us succeed:
:
, I leave this legacy to the one night in shining armor who can wield this sword from the stone.
