jasonintoronto

is it a battery? kinetic?

Kolia

iTrader: (2)

Probably powered by a magnetic field from the emiter/receiver in the wheel wells.

When the module passes through it, an electric current is generated and a pressure reading is taken.

The Pirelli system works that way.

Jetpilot718

So the unit in the wheel itself is not powered?? How the hell does that work?? Anyone know?

Jetpilot718

Actually, now that I think about it, Im pretty sure it is kinetic. Think about it, the TPS doesnt work until your wheels are MOVING. If they were self powered, this would not be an issue. Also, how retarded would it be to have to remove the tire to change a battery in the TPS module? heh

Jason@Performance

iTrader: (11)

good question... :-/

Jetpilot718

Come onn, you mean you havn't opened one of those things up yet?? heh Shame on you.. you're a nissan tech!

DavesZ#3

iTrader: (26)

Actually, I doubt it would be kinetic. It's probably as Kolia stated - it uses a magnetic field. The reason that you must be moving for them to work is because the sensors in the wheel must move through the field generate by the fixed transducers near each of the four wheels.

Basic electromagnetism at work here. If you move a coil through a magnetic field you can generate a current. You have to get the wheels spinning so the coil in the sensor passes thru the magnetic field often enough to generate enough power to run the sensor.

kcobean

iTrader: (2)

Well, according to the service manual (which doesn't come right out and give you the answer), there is no battery in the sending units, and there is no emitter in or near the wheel wells. Therefore, it would make sense that they have to be kinetically powered, much like a 'self-winding watch'. The confusing part is that self-winding watches require movement in two directions (like swinging arms while walking). Once a wheel is spinning, what "reciprocating motion" is there to generate power? The other thing that is confusing is that there is a "transmitter activation tool" that can be used to power up the transmitters without driving the car for the purposes of transmitter identification/learning. That would make me believe that these are RFID devices that are powered by an external source as Kolia suggested, but that source is a mystery even after reviewing the service manual

Also interesting to note is that the identification process for which sensor is in which wheel can be accomplished by placing the computer into a learning mode and then setting the tires to specific, varying pressures at each corner (3 pounds difference per wheel) and then driving the car. When the sensors generate their readings for the varying pressure, the computer knows that "x" pounds is LF, x+3 is RF, x+6 is LR and x+9 is RR. Pretty sneaky way of getting it done.

DragonGcoupe

LOL. What if all our TPS were just Nissan BULL! LOL.

That was a funny thought, and I'm sure they couldn't BS something as big as that without someone ripping them apart for it.

kcobean

iTrader: (2)

I picked up a huge chunk of metal in my left rear tire and it took the wheel about 5 minutes to go flat. I can assure you that the TPS system works beautifully.

Michael-Dallas

Bingo. They have to be RFID devices. The TPS module sends out an RF wave and the TPS "reflects" its ID back. How it calculates tire pressure could be one of a few ways: 1- the RF wave is converted to electricity to power the TPS, or 2- the TPS module counts the number of tire revolutions, or ???

My guess is that it is passive (i.e. not converting the RF wave to electricity).

Michael.

DavesZ#3

iTrader: (26)

Actually, we're all wrong. They're battery powered.

See section WT-19 of the 2004 service manual. There are references there to diagnostic codes that indicate low battery in each of the 4 transmitters in the TPS units.

There is also a section there on the Transmitter Activation Tool which allows a tech to activate the TPS sensor in the shop - no wheel rotation. Therefore it's not kinetic or induction based.

kcobean

iTrader: (2)

Well I'll be a monkey's uncle!!! Found it in the 2003 manual as well!!! So, the rotation of the tire must activate some centrifugal on/off switch so that the transmitters aren't "on" all the time. Good find.

WayneTN

Does anyone know for a fact that, if a TPM on one wheel goes out, the warning light on the dash will light up? I had a TPM on the right front either go out (or it was damaged by the dealer during tire changeout), and on trips of over about 30 minutes the light will come on. There is no pressure problem; all tires will go from about 35 psi to about 39 psi and the light just comes on. It stays on until you stop for gas and then 30 - 35 minutes later it comes back on.

Is the failed TPM the problem?

tia,
WayneTN

kcobean

iTrader: (2)

There are a number of reasons that the light could come on. The troubleshooting portion of the manual has lots of cause/code tables for the TPS system. I'll take a look tonight and see if I can narrow down a few of the reasons that may happen. One reason (now that we know it to be true) could be a low battery. When a unit sits for awhile, it's battery 'rests', then after you start driving and the units begin sending, one or more of their batteries drops below normal operating voltage and throws a code...

The dealer would use the CAN port to diagnose this, and it should be covered under warranty, yes?

Florida350zrt

If you think about it, at one point the valve is at top Dead Center, so to speak.
When the wheel rotates 360 degrees it does change direction when it reaches the bottom and then again when it reaches the top.

kcobean

iTrader: (2)

Hmmm....Without getting too much into Geometry here, I would have to disagree. You're thinking along a plane (the tangent of the circle, and in this case, horizontally), but the sensor is travelling in a circle at a constant velocity, so the force exerted on the sensor is always along the radius of the circle, thus no "reciprocating force" is ever applied that could swing a "winding arm" or other kinetic device.

I'll agree with you that the sensor is changing directions though, as many times per second as you care to measure. It is, after all, a circle.

Hey, that gives me an idea....What if I were to make an engine with "pistons" that spun around in a circular type motion. They could achieve much higher RPMs! I'll call it "The Rotary"....Nah, people would think I'm a ****(el) for suggesting such a thing.

God I hate math.

ChinaClipper

iTrader: (2)

Interesting to read the replies so far to this question, as I have previously posted on this forum as to how TPS's work, having previously contacted the UK company that makes the TPS for Nissan. The TPS is powered by an integral lithiuum battery that is permanently potted into the plastic housing along with the sensor. To preserve battery life, you have to rotate the wheel fast enough to activate an integral switch to switch the battery "on". The Nissan dealer device (probably magnetic) activates the TPS battery switch to on with the wheel/tire static. Per the manufacturer, the battery has "an average expected life under normal use, of approximately seven years." When signal is lost on a TPS, whether due to damage or battery failure, the indicator light on the dash will light up after a single BEEP as opposed to the repeated BEEP warning of a low tire.
Hope this accurate information helps!

kcobean

iTrader: (2)

Cool stuff! Thanks for all the good details.

Michael-Dallas

Damnit MikeQ, you can be really cruel sometimes. Well... at least I was close...

Ugh. Battery powered? Are the batteries at least replaceable or do we have to spend $250/ea to replace?

Michael.