Tire Pressure Monitoring System

[NitroTech]

Here's a description on how the Tire Pressure Montioring (TPM) systems on the Nitro's work. There are 2 systems Base and Premium.


BASE TIRE PRESSURE MONITORING

The tire pressure monitoring system is designed to operate without loss of function for all OEM tire construction for this vehicle. The wheel sensor shall monitor tire pressure, air temperature inside the tire, wheel acceleration and the sensor internal battery status for all four active road tires. The sensor will broadcast this information, along with a unique 32 bit ID, to a central receiver circuit located inside the WCM. The information received by the WCM will be decoded and stored in memory (RAM) in the WCM. If a "warning or "fault" condition exists, the WCM will send a bus message request to illuminate the yellow telltale and to sound the chime.

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 yellow telltale. 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 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. (Note: For vehicles with optional wheel/tire sizes and significantly different tire placard pressures, the placard pressure value and the low-pressure threshold value's programmable using a scan tool to accommodate the customer selected wheel/tire combinations recommended by DaimlerChrysler).

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 warning lamp will extinguish once the updated tire pressures have been received.

The 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 for a premium tire pressure monitoring system (TPMS) is the same as the base TPMS, but the premium TPMS can display text messages and a graphic display of the tire pressure on the information cluster. If a low pressure condition is detected, in addition to a chime and the indicator lamp turning ON, a low pressure text message indicating which tire is low will be displayed in the instrument cluster for 3 seconds. This text message will be followed by 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 and the system returns to normal within approximately two minutes time. If a system fault is detected, in addition to the flashing lamp, a “Service Tire Press.System” text message will be displayed in the instrument cluster, and the 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

A Premium Tire Pressure Monitoring System (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 update the graphic display when necessary.

For both the premium and base TPMS, 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.

[DAYLEY/CHALLENGER]

WOW. I guess that is why we have to pay so much for vehicles. Engineers have a lot of pressure to come up with new things and then explain how they work!! This is really an informative post. Thanks NitroLarry

[Skulman]

So this system only works on OEM tires & wheels? Or can it be tranfered to after market wheels?

[NitroTech]

You should be able to install the sensors in aftermarket rims. Haven't personally done it but I sure others here could verify if it does.

[warriorbob]

Originally Posted by NitroTech

You should be able to install the sensors in aftermarket rims. Haven't personally done it but I sure others here could verify if it does.

have aftermarket American Racing rims

the sensors went on the new wheels with no problem and work perfectly

[Skulman]

WarriorBob, The rims you put on, are they the same size? I want to put 20's on mine when I get it and it only comes with 17's, think it will make any difference?

[NitroRico]

Originally Posted by warriorbob

have aftermarket American Racing rims

the sensors went on the new wheels with no problem and work perfectly

Can you share how to put it back on.
I have aftermarket 22's and keep getting the annoying warning.

The dealer said he would charge $70 a tire to put it back, lol
I told them its not that big of a deal, but nice to have.

[AirJunky]

Originally Posted by NitroRico

Can you share how to put it back on.
I have aftermarket 22's and keep getting the annoying warning.

The dealer said he would charge $70 a tire to put it back, lol
I told them its not that big of a deal, but nice to have.

Remove the tire from the rim, install the sensor & schrader valve assembly, reinstall the tire. Your tire dealer should have done this for you for no cost considering what you paid for the 22s.

I got a TPM warning last Friday. It lasted about 10 seconds & I haven't seen it since. All the tires are are 35 or 36 PSI.

[HighVoltageNITRO]

One other thing about the wheel sensors. If you have to buy a new set, they run about $130 USD for a set. Another thing, that is just for 4 wheel sensors, you have to ask for the special nuts separately. They cost about $6 more for a set of 4.

[Waldorf]

I had a scare yesterday with the tire sensors. It started chirping at me and said the pressure was 68 kPA for one tire when the rest were at 268 kPA!! I went to put air in the tire and it was fine. I checked the on-dash readout again and it was fine. What would cause this false alarm reading?