KenTheTPMSMan
03-07-2013, 08:53 PM
TPMS (Tire Pressure Monitoring System), also known as TPWS (Tire Pressure Warning System), has been around for a few years now, but starting next year (2008) *ALL* new cars are required to have a "direct" type TPMS system, with pressure transducer mounted inside the wheel wirelessly transmitting tire pressure data to a control unit as the car is driving down the road, in order to alert the driver if any tire loses pressure while driving.
Any shop doing tire work, even if it's just tire rotation, will need to be familiar with these systems before they start rolling in the door. Learning about TPMS on the job will likely lead to dissatisfied customers and potentially costly damage to your customer's car. I started this article as a memo to Art's employees, but figured I may as well make a web page of it, since the information may be useful to our customers, or maybe even other shops.
First, a little history. Most of the early tire pressure monitoring systems used the anti-lock brake system's wheel speed sensors to determine if a tire was low on pressure. If a tire is low, the effective circumference is reduced, so the wheel will spin more times than the other three at the same vehicle speed. The ABS control unit would notice this, and turn the TPMS light on. This was an inexpensive system because it used the components already installed on the car. The problem was that it was not very accurate. This type of TPMS is called "indirect" TPMS.
The currently mandated "direct" TPMS systems use a pressure transducer mounted inside the wheel to measure the pressure, and send that information wirelessly to one or more antennas on the body of the car. Almost all of the TPMS system manufacturers attach the TPMS sensor to the base of the valve stem, but there are a few that are held to the rim with a band.
One of the issues with sending tire pressure information via radio transmission is -- How will the TPMS ECU be able to tell which sensors it's supposed to monitor? In other words, when all the cars driving on the road have TPMS, how will the TPMS ECU be able to differentiate between the sensors on "its" car and the sensors on the car driving next to it?
Changing the broadcast frequency might work (like tuning to a radio station), but there is not enough available spectrum to support a "station" for each car on the road. The solution is to give each sensor a unique ID number, which it will broadcast along with the pressure information. Each sensor ID will be "registered" in the TPMS ECU, and the TPMS ECU will only pay attention to signals that start with a registered ID. Those of you familiar with setting up Bluetooth devices are familiar with this process. It's called pairing with Bluetooth instead of registration, but it's more or less the same thing.
So if you need to replace a TPMS sensor, how do you tell the TPMS ECU about it? So far, the only solution I know of is using a factory scan tool to initiate the registration process. (A screen from the Honda HDS scan tool is on the right.) However, I'm sure that this will be changing very soon if it hasn't already. We have factory scanners for Toyota/Lexus/Scion, Honda/Acura, and Nissan/Infiniti. The Mazdas and Subarus may present a challenge for a while. Subaru is currently blocking access to their Subaru Select Monitor III to all but dealers. (One more reason not to buy a Subaru). We'll probably be buying the HDS3000, Subaru's alternate "dealer level" scan tool, which reportedly does less and definitely costs more. Mazda is using the IDS scan tool, which is a Ford product, much like most of the current Mazda line. We've toyed with the idea of dropping Mazda from our line of cars, but so many of our customers are buying the Mazda 3, it's hard to do. There will likely be good aftermarket scanner support for MaFordzdas. GM and Ford are usually well supported by Snap On, OTC, and others.
We've been fortunate enough to avoid breaking any TPMS sensors so far (more on how to avoid damaging sensors later), so most of what I know about registering a new TPMS sensor is from reading. TPMS registration works in much the same way as registering new immobilzer key. A simple "Simon Says" type operation with the scanner. I'll pass along a tip I was given for Toyota: be sure to check the current sensor IDs with a scanner, and write them down accurately before beginning the registration process. During the registration process, all sensor IDs are erased, and you'll need to enter each sensor ID, even the ones for for the sensors that are not new. If you fail to do this, you'll need to dismount the tire to read the ID number off the side of the sensor according to my dealer source. Although not an official Toyota procedure, a TPMS tool, like the one made by OTC and others (more on the tools later) can be used to retrieve the ID numbers without the tire dismount. It would be easier to just write the numbers down before starting.
So what do those little hand held TPMS tools do? I'm sure your tool vendor has been trying to get you to buy one for the last six months or longer, but depending on the makes you repair, you may not have seen the need. Soon you will.
Purpose #1: All variants of these tools can "activate" a TPMS sensor. When the TPMS ECU is in "learn mode", activating the sensors in a predetermined sequence tells the TPMS ECU where the wheels are. The sequence usually starts with the left front wheel, and moves clockwise. Learning is necessary on some cars even after a simple tire rotation. Other cars, such as the Toyotas (so far) do not need a TPMS tool to activate the sensors for any reason. On Hondas, the TPMS tool is only needed for diagnosis, and is not required for rotations or other tire maintenance.
The TPMS tool does only half the job. It will not put the TPMS ECU in the learn mode. Right now, it's looking like a factory scan tool may be the only way to get some cars into the learn mode. For instance, all Honda/Acura (so far) require the factory scan tool (HDS) to initiate the learn mode. This may be more of an investment than many multi-make shops want to make.
Purpose #2: Some TPMS tools will also gather information from the TPMS sensor, such as ID number, tire pressure, and tire temperature. This can be very handy as a quick function-check before replacing tires on a car with a TPMS light on. You can quickly verify the TPMS sensors are working before dismounting the tires, and potentially get blamed for a non-working sensor. Also might be very handy if you forget to write down the ID numbers before starting the registration process on a Toyota.
Any shop doing tire work, even if it's just tire rotation, will need to be familiar with these systems before they start rolling in the door. Learning about TPMS on the job will likely lead to dissatisfied customers and potentially costly damage to your customer's car. I started this article as a memo to Art's employees, but figured I may as well make a web page of it, since the information may be useful to our customers, or maybe even other shops.
First, a little history. Most of the early tire pressure monitoring systems used the anti-lock brake system's wheel speed sensors to determine if a tire was low on pressure. If a tire is low, the effective circumference is reduced, so the wheel will spin more times than the other three at the same vehicle speed. The ABS control unit would notice this, and turn the TPMS light on. This was an inexpensive system because it used the components already installed on the car. The problem was that it was not very accurate. This type of TPMS is called "indirect" TPMS.
The currently mandated "direct" TPMS systems use a pressure transducer mounted inside the wheel to measure the pressure, and send that information wirelessly to one or more antennas on the body of the car. Almost all of the TPMS system manufacturers attach the TPMS sensor to the base of the valve stem, but there are a few that are held to the rim with a band.
One of the issues with sending tire pressure information via radio transmission is -- How will the TPMS ECU be able to tell which sensors it's supposed to monitor? In other words, when all the cars driving on the road have TPMS, how will the TPMS ECU be able to differentiate between the sensors on "its" car and the sensors on the car driving next to it?
Changing the broadcast frequency might work (like tuning to a radio station), but there is not enough available spectrum to support a "station" for each car on the road. The solution is to give each sensor a unique ID number, which it will broadcast along with the pressure information. Each sensor ID will be "registered" in the TPMS ECU, and the TPMS ECU will only pay attention to signals that start with a registered ID. Those of you familiar with setting up Bluetooth devices are familiar with this process. It's called pairing with Bluetooth instead of registration, but it's more or less the same thing.
So if you need to replace a TPMS sensor, how do you tell the TPMS ECU about it? So far, the only solution I know of is using a factory scan tool to initiate the registration process. (A screen from the Honda HDS scan tool is on the right.) However, I'm sure that this will be changing very soon if it hasn't already. We have factory scanners for Toyota/Lexus/Scion, Honda/Acura, and Nissan/Infiniti. The Mazdas and Subarus may present a challenge for a while. Subaru is currently blocking access to their Subaru Select Monitor III to all but dealers. (One more reason not to buy a Subaru). We'll probably be buying the HDS3000, Subaru's alternate "dealer level" scan tool, which reportedly does less and definitely costs more. Mazda is using the IDS scan tool, which is a Ford product, much like most of the current Mazda line. We've toyed with the idea of dropping Mazda from our line of cars, but so many of our customers are buying the Mazda 3, it's hard to do. There will likely be good aftermarket scanner support for MaFordzdas. GM and Ford are usually well supported by Snap On, OTC, and others.
We've been fortunate enough to avoid breaking any TPMS sensors so far (more on how to avoid damaging sensors later), so most of what I know about registering a new TPMS sensor is from reading. TPMS registration works in much the same way as registering new immobilzer key. A simple "Simon Says" type operation with the scanner. I'll pass along a tip I was given for Toyota: be sure to check the current sensor IDs with a scanner, and write them down accurately before beginning the registration process. During the registration process, all sensor IDs are erased, and you'll need to enter each sensor ID, even the ones for for the sensors that are not new. If you fail to do this, you'll need to dismount the tire to read the ID number off the side of the sensor according to my dealer source. Although not an official Toyota procedure, a TPMS tool, like the one made by OTC and others (more on the tools later) can be used to retrieve the ID numbers without the tire dismount. It would be easier to just write the numbers down before starting.
So what do those little hand held TPMS tools do? I'm sure your tool vendor has been trying to get you to buy one for the last six months or longer, but depending on the makes you repair, you may not have seen the need. Soon you will.
Purpose #1: All variants of these tools can "activate" a TPMS sensor. When the TPMS ECU is in "learn mode", activating the sensors in a predetermined sequence tells the TPMS ECU where the wheels are. The sequence usually starts with the left front wheel, and moves clockwise. Learning is necessary on some cars even after a simple tire rotation. Other cars, such as the Toyotas (so far) do not need a TPMS tool to activate the sensors for any reason. On Hondas, the TPMS tool is only needed for diagnosis, and is not required for rotations or other tire maintenance.
The TPMS tool does only half the job. It will not put the TPMS ECU in the learn mode. Right now, it's looking like a factory scan tool may be the only way to get some cars into the learn mode. For instance, all Honda/Acura (so far) require the factory scan tool (HDS) to initiate the learn mode. This may be more of an investment than many multi-make shops want to make.
Purpose #2: Some TPMS tools will also gather information from the TPMS sensor, such as ID number, tire pressure, and tire temperature. This can be very handy as a quick function-check before replacing tires on a car with a TPMS light on. You can quickly verify the TPMS sensors are working before dismounting the tires, and potentially get blamed for a non-working sensor. Also might be very handy if you forget to write down the ID numbers before starting the registration process on a Toyota.