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Tire Pressure Monitoring System Operation

39K views 69 replies 30 participants last post by  bigtsr 
#1 ·
OPERATION



NOTE: Premium Tire Pressure Monitoring is the only system used on this vehicle. Because the Premium system is based upon the Base system, both are explained here.

BASE TIRE PRESSURE MONITORING

The tire pressure monitoring system (TPMS) is designed to operate without loss of function for all OEM tire construction for this vehicle. Sensors, mounted to each road wheel as part of the valve stem, transmit an RF signal indicating their individual pressure to a receiver located in the Wireless Control Module (WCM), commonly referred to as the Sentry Key Remote Entry Module (SKREEM). On a Domestic vehicle, the TPM sensor operates on a 315 MHz radio frequency. Export vehicle sensors operate on a 433 MHz radio frequency. These transmissions occur approximately once every minute at speeds over 15 mph (24 km/h).

If the TPM system detects that the tire pressure in any road tire is going low, beyond the Low Pressure (lamp) ON threshold (see placard table below), the TPM system will continuously illuminate an indicator lamp. If a system fault is detected, the indicator lamp will flash on/off for 60 seconds, once every 10 minutes.
If the WCM detects a warning or fault condition at ignition key "on" it will wait ten seconds +/- 10 % before sending the first request to illuminate the indicator lamp. This will assure that the display module has concluded its bulb check period. The display module will request a chime once per ignition cycle for each "warning" or "fault" condition detected. A "warning" or "fault" condition will remain enabled until the problem causing the condition is corrected and removed/reset.
The WCM shall continuously monitor for the receipt of tire pressure RF message transmissions from the wheel sensors during both the ignition key "on" and key "off" cycles. The wheel sensor ID’s and the location of each sensor (e.g. Tire 1, Tire 2 etc.) are stored in the WCM non-volatile memory during the initial Manufacturing Plant Process, or during a service procedure, as required.
The TPM System will continue to warn the driver of low tire pressure as long as the condition exists, and will not turn off the indicator lamp until the tire pressure is at or above the Low Pressure (lamp) OFF threshold (see placard table below). The system will automatically update and the TPM indicator lamp will extinguish once the updated tire pressures have been received.
Tire pressure will vary with temperature by about 1 psi (6.9 kPa) for every 12°F (6.5°C). This means that when the outside temperature decreases, the tire pressure will decrease. Tire pressure should always be set based on cold inflation tire pressure (placard pressure). This is defined as the tire pressure after a vehicle has not been driven for more than 3 hours (and in outside ambient temperature). The tire pressure will also increase as the vehicle is driven; this is normal and there should be no adjustment for this increased pressure. For a system fault, the system will return to normal once the WCM receives a valid transmission from that sensor location.
PREMIUM TIRE PRESSURE MONITORING

The operation and lamp/chime strategy of the Base Tire Pressure Monitoring System (TPMS) also applies to the Premium TPMS, but the premium TPMS can display text messages and a tire pressure graphic display on the information cluster. If a low pressure condition is detected, in addition to a chime and indicator lamp turning ON, the Electronic Vehicle Information Center (EVIC) will show a graphic display of the pressure value(s) with the low tire(s) flashing. Once pressure in the suspect tire raises above the Low Pressure (lamp) OFF Threshold (see placard table below), the lamp will go out once the WCM receives a valid transmission from the sensor. If a system fault is detected, in addition to a chime and a indicator lamp flashing, a “Check TPM System” text message will be displayed in the instrument cluster, and the tire pressure graphic display will have “- -“ in place of the pressure value. The system will return to normal once the WCM receives a valid transmission from that sensor location.
The Premium TPMS determines the location of the tire pressure sensors by using transponders located in three of the four wheel wells on the vehicle. A fourth transponder is not necessary in the remaining wheel well due to the process of elimination theory. Once the system knows the location of the first three sensors, it assumes the location of the fourth tire pressure sensor, and updates the graphic display when necessary.


For both the premium and base TPM, the recommended "Placard Pressure", "Low-pressure Threshold" and “Hysteresis Pressure Values” for the tires installed on the vehicle, are stored in the WCM non-volatile memory during the initial Manufacturing Plant Process, or during a service procedure, as required.


On vehicles equipped with the premium TPM system, the Wireless Control Module (WCM), commonly referred to as the Sentry Key Remote Entry Module (SKREEM), uses transponders (trigger modules) located in three of the four wheel wells on the vehicle to provide it with the location of the tire pressure sensors on the vehicle. Like the base system, the WCM receives RF signals from all four rotating wheel speed sensors. When the WCM needs to know which sensor is located at a particular location on the vehicle, it directs the transponder at that location to send out a low frequency signal to excite the nearby sensor. The WCM then receives that excited signal and knows where that sensor is located. This auto-locating process only happens in the first 10 minutes of any WCM cycle while traveling at speeds above 20 mph (32 km/h). (The auto-locating process will start again only if the vehicle has been shut off for approximately 20 minutes or longer). Once the WCM has performed this to the three locations that have transponders, it uses the process-of-elimination theory to know that the fourth sensor ID signal is coming from.
 
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#64 ·
The standard for legislation would have been written for a minimum. It was for US car drivers who were buying top heavy trucks and flipping them like Explorers.

Since then the price and performance would have improved considerably suggesting the trigger margins would have tightened.
 
#65 ·
You have it backwards. When you're dealing with a number and you don't want it below a certain number; you give it a maximum amount it can drop to. By you're interpretation; any pressure below the 25% would be acceptable; i.e., with 32psig being optimum then anything below 25.6psig would trigger the TPMS display. The law was written for anything 25.6psig and above.
 
#66 ·
Probably a matter of semantics.

The pressure drop can be a maximum or 25 % of rated inflation pressure.
The pressure in the tire can be a minimum of 75 % of rated inflation pressure.

This is what happens when government tries to get involved in science and technology. they create confusion.

Science and technology are for scientists, engineers, and technicians - not politicians (spelled l a w y e r s)
 
#67 · (Edited)
Owners of newer vehicles equipped with the TPMS system ignore the warning lights and fail to correct the condition. In addition, there are still millions of older vehicles on the road without TPMS.

Since underinflated tires are difficult to detect visually, without monthly checks to ensure tires are inflated to the proper pounds per square inch (PSI) as indicated by the vehicle owner’s manual, drivers could be increasing their risk of a crash involving serious injuries or death.

As reported in The Detroit News, new study of crash data from 2005-2007 by the National Highway Traffic Safety Administration (NHTSA) found that 5 percent of vehicles involved in crashes had tire problems – either underinflated or poorly maintained tires.

Furthermore, vehicles with tires underinflated by 25 percent were three times as likely to be involved in a crash-related to tire problems. Sixty-six percent of tire-related crashes involved passenger cars.

A 2008 model year or newer passenger car, light truck or van under 10,000 pounds gross weight is equipped with a tire pressure monitoring system (TPMS) as mandated by federal law. The purpose of TPMS is to detect and warn the driver when tire pressure dips below 25 percent the recommended level in any tire.

http://www.thecarconnection.com/news/1076372_tire-pressure-at-fault-in-5-percent-of-accidents-study
 
#68 ·
Some models are more sophisticated than others,
mine reads out in KPA/PSI with a warning light and
audible alarm.
 
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