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Discussion Starter #1
I replaced my stock 240 wheels with my cup wheels, and now I am getting the tire pressure fault warning. The tire icon is lit up on the dash, and won't go away. :sad: I guess the dash is waiting to get a signal from the wheels, but is registering a fault when it cannot make contact.

Does anyone know how to defeat this, or how to fool the car into thinking the wheels are there and properly inflated? Thanks.
 

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Where is the sensor located in the wheels? Is it in the valve?

If it can be removed, it can be replaced onto/into the cup wheels, no?
 

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I replaced my stock 240 wheels with my cup wheels, and now I am getting the tire pressure fault warning. The tire icon is lit up on the dash, and won't go away. :sad: I guess the dash is waiting to get a signal from the wheels, but is registering a fault when it cannot make contact.

Does anyone know how to defeat this, or how to fool the car into thinking the wheels are there and properly inflated? Thanks.
From the service manual:

GH.6 - TYRE PRESSURE MONITORING SYSTEM (TPMS) - USA ONLY
All USA Elise/Exige models from ‘08 model year onwards are fitted with a tyre pressure monitoring system.
A sensor incorporated into each of the tyre valves monitors the air pressure inside the tyre, and supplies an
onboard control module with this data by radio transmission. If any tyre pressure should fall below 75% of the
recommended value, an alert message is sent to the instrument panel, and the tyre pressure tell tale
will light up amber. The fuel gauge display will then be overwritten with a message to indicate which tyre is
concerned, with text such as: LF Low (left hand front tyre low pressure). This message will show for 5 seconds
before the display reverts to the fuel level bar graph, but will repeat for 5 seconds at 30 second intervals.
The TPMS incorporates self-malfunction recognition, and if a fault is detected, the tell tale will flash for one
minute and then remain constantly lit. The LCD panel will also flash ‘TPMS FAULT’ for 5 seconds, and repeat
at 30 second intervals; no indication of low tyre pressure will be displayed.
Tyre fitters and service technicians should be made aware that TPMS is fitted, and that the tyre valves
include pressure sensors. If the emergency tyre inflator aerosol has been used, it will be necessary to renew
the tyre valve/pressure sensor. If a fault is indicated after wheel or tyre replacement, it is likely that a sensor
has been incorrectly fitted or damaged. If a tyre valve is renewed, or is moved to a different wheel position, the
TPMS will automatically identify the new configuration.
Note that the pressure sensors are powered by integral batteries, with an average service life of 10 years.
It is recommended to renew all pressure sensors at this time interval.
If renewing a wheel, ensure that only a TPMS compatible wheel is used, as the installation angle of the the
tyre valve is modified to accommodate the pressure sensor. Compatible cast wheels are identified by 'TPMS'
within one of the recesses in the hub mounting face. On TPMS compatible forged wheels, the profile of the
wheel rim outboard of the central well, is modified in order to allow local machining around the valve hole on
the inside of the rim to provide a shallower installation angle. If no machining is evident, the wheel is not TPMS
compatible. In addition, a batch code is engraved onto the inner rim in the form of 'PS123456'. The first three
numbers indicate the week and year of manufacture, and any wheel with a code of PS267### (week 26 of
2007) or later, will be TPMS compatible. TPMS type wheels may be fitted on all cars.
 

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An active TPMS is now a federal requirement. This means pressure sensors on each wheel transmitting to a central control unit. Part of the requirement is for there to be a warning indicator if the system is inoperative due to failure to receive a signal from any of the four wheels. Passive systems previously used on some cars, which detect low pressure from changes in wheel rotational speed, no longer meet the federal requirement.
 

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I replaced my stock 240 wheels with my cup wheels, and now I am getting the tire pressure fault warning. The tire icon is lit up on the dash, and won't go away. :sad: I guess the dash is waiting to get a signal from the wheels, but is registering a fault when it cannot make contact.

Does anyone know how to defeat this, or how to fool the car into thinking the wheels are there and properly inflated? Thanks.
you can purchase TPMS sensors form Tire Rack for about $350 (I assume for 4). I did not purchase them, the light dosn't bother me that much.
 

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OEM may be cheaper...

I was quoted a price of $77 for each sensor, or roughly $308.

My concern about using after market sensors is the compatibility with the installed receiver in the Lotus. Perhaps they have standard broadcasting frequencies or signals but I would check to make sure.

Hopefully someone will figure out a way to subvert the system. My idea was to remove the four sensors, make them think they are experiencing full pressure, and then tape them to the wheel well liners. Of course I would never suggest such a thing unless you check your tire pressures every day before starting out...

Michael
 

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Discussion Starter #7
I think you are right, the OEM may be cheaper. I was quoted about $70 each at Fox Valley, but they are back ordered right now. :sad: I saw on the Subie board that a guy made a small canister out of PVC pipe and put three of the sensors in, and the fourth one was mounted in the lid so you could inflate the canister. Filled the canister with air, and put it in his trunk. I will probably do something like that unless someone somewhere comes up with a device to fool the system. The light on all the time is annoying.
 

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canister idea may not work

I liked the idea of putting the pressure sensors in a canister and then inflating it.

However I am not sure it will work in the Lotus. There is some ability to detect which sensor is where and then notify the driver which tire is under inflated. When a sensor is relocated to a different wheel position, the system can tell.

With all the sensors in the canister, I am not sure how the system will be able to tell them apart. It may throw a fault just because of that.

It is good to know others makes will have the same problem. Perhaps the next one of us that needs to remove a tire can take a look at the system and determine the manufacturer. That will be the first step in developing a solution.

Michael
 

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It is good to know others makes will have the same problem. Perhaps the next one of us that needs to remove a tire can take a look at the system and determine the manufacturer. That will be the first step in developing a solution.

Michael
Three primaries:
Infineon, Freescale, and TI.

TI's was a batteryless solution (not sure if it ever made it to market) so it's off the table. My money is on Infineon.
:)
 

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Maybe I'm missing something, but does the tire pressure sensor measure the difference between the tire's pressure and ambient pressure, or between tire pressure and a reference pressure inside the sensor (pressure capsule?). If it's the former, putting the sensors completely inside a pressurized canister won't work. Anyone know?
 

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Maybe I'm missing something, but does the tire pressure sensor measure the difference between the tire's pressure and ambient pressure, or between tire pressure and a reference pressure inside the sensor (pressure capsule?). If it's the former, putting the sensors completely inside a pressurized canister won't work. Anyone know?
Gernally, it's direct measurement of pressure (and temperature) against "placard" (reference) pressure.
 
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