I'm in the market for aftermarket wheels for my car, will the tire pressure monitor still work without the factory wheels?

 

wheeldealer,

I apologize for giving a long answer to your question, but it may be helpful to know how the tire pressure monitor (TPM) system works.

Each wheel contains a tire pressure sensor (TPS) module that is part of the valve stem assembly. The TPS is powered by an internal, non-replaceable battery. To save battery power, the TPS is only activated when the car reaches approximately 20 mph and a roll switch is closed. Approximately every 30 seconds the TPS monitors the internal pressure of the tire. If the internal pressure is below one of two programmed values (low pressure, or critical pressure), or if the internal pressure is more than 1 psi below the value last recorded by the TPS, then the TPS will transmit a warning radio signal approximately once every 60 seconds. This signal is transmitted through the valve stem which acts as a transmitter antenna. In addition to the warning code (low pressure, critical pressure, or 1 psi change in pressure per 30 seconds), the TPS also sends a unique wheel identification code.

The TPS signal is received by the tire pressure monitor (TPM) module which resides in the HomeLink Universal Transceiver, which also contains the garage/gate door opener. When the TPM receives a signal from one of the TPS modules, it sets a trouble code and indirectly turns on the tire pressure warning light and/or activates a chime (if the critical pressure threshold was reached) through the Body Control Module (BCM).

If the TPS units properly fit your new wheels, then they should work fine. However, since each TPS has a unique code identifying the wheel in which it resides, you need to make certain that each TPS goes back on the same corner of the car from which it came. And if you rotate your tires/wheels, then you need to have your Chrysler dealer reprogram the TPS units so that they correctly identify on which corner of the car they now reside. Also, since the TPS units are constructed from aluminum, you need to make certain that the new wheels are also constructed from aluminum. If not, corrosion in the TPS units can occur from placing dissimilar metals in contact with each other, and this corrosion can cause the TPS to fail.

I hope this helps, and again, I apologize for the long-winded answer.

 

I remember reading this in the service manual, but I wonder if this is really how they work. The only time my TPM light has ever come on was when the car sat out overnight and the temperature dropped significantly. The light came on when the car was first started and hadn't even moved. It seems that if the monitor can detect when the tire pressure has dropped while the car is sitting, it must be transmitting all the time. Maybe this was changed after the service manuals were published.

 

My guess is that the pressure is monitored when the ignition is on or engine started./

I would hope that those batteries, referred to, get recharged constantly when engine is running.

 

The batteries are in the sensor/transmitter inside the wheel, so there is no way for them to be recharged.

 

If this is the case, then we can expect to have to replace batteries after a few years. I wonder if when they go dead, what happens? Hopefully the TPM light & beeper doesn't continually stay on .

 

mbepic,

The same thought crossed my mind about the lifespan of the batteries in the sensors. C_Plunkett is correct that there is no way the batteries can be recharged. Since the batteries are non-replaceable, I assume that every few years we will have to replace the entire valve stem assembly.

C_Plunkett,

I think there are too many variables in the equation to assume that the sensors are transmitting all the time based on your experience in cold weather. I agree that something probably did not function as it should have due to the cold, bit it could have been the roller switch in the sensor (which caused it to transmit when it shouldn’t), it could have been the pressure sensor itself, or the TPM module in the Universal Transciever, or the Body Control Module (BCM), or something in the instrument panel. My guess is that something somewhere generated a trouble code and a scan might turn up some clue as to what really happened.

The service manual specifies 15 different Diagnostic Test Codes (DTCs) that can be raised by the TPM, including a TPS low battery code. I notice that the “B” schedule maintenance service calls for a check of the tires for damage and pressure. I am guessing that the dealer runs the Pressure Verification Test during “B” maintenance. If so, the low battery would be found then. I’m sure that our local Crossfire certified technicians can verify that.

When you sit in the cockpit and look around, all appears clean and relatively simple on the surface. But below the surface, there is a huge amount of complexity. Frankly, I am fascinated by all this gadgetry below the surface.

 

I would guess that when the battery goes dead, that the TPM light would come on to indicate that there is a problem. I don't have the manual in front of me (it's at work), but I seem to remember that there is an error code if the receiver hasn't recieved a signal within a specified amount of time. Therefore, when the battery dies, you'll have to have it replaced or live with the dash light on all the time.

 

this is what I found when investigating the purchase of winter rears..." Warning! The Crossfire uses a factory TPMS system. The existing transmitters must be reused or a new set must be purchased for mount and balance packages. TPMS must be programmed by a dealer. " Hope this helps us both!

 

Has anybody a picture of the tire pressure monitor because we dont have this feature on the German version of the XF.
Thanks
Steffen

 

I don't think it goes on only over 20mph. Mine has turned on during cold weather right when starting the car. I've checked with a tire pressure gauge and they are low. Later on as it warms up, I'll start my car after work and there will be no light. So I think they are always on.

 

I can confirm that the TPMS is ON whenever the ignition is 'on'. Its a great feature but certainly succeptible to temperature variations when you are on the edge of acceptable tire pressure.

 

I believe my light stays on because they were submerged in water. Could this cause them (battery) to malfunction? If so, can they be removed and cleaned / repaired or replaced? Can the pressure range be reset w/o dealer?

 

The dealers ask about $60 for the TPS stems but a good Google seach brings them in at $28-32 depending on the online dealer. Got a set for my snow tires and wheels. Dealer reset them for free. They are dead simple and the batteries should last more than 5 yrs with current battery and software technology with the very low current draw.

 

If water somehow got into the transmitter it could have shorted out, and then the light would come on since the receiver isn't getting a signal anymore. I don't really see how water would get into the transmitter since the positive air pressure in the tire should prevent water from getting past the valve stem core. If the cap is missing or the o-ring seal is damaged then it's possible that the core could be contaminated and would prevent a signal from being sent since it is the antenna. You might try removing the cores to see if they are corroded. The cores could be replaced, but they are specially coated to prevent galvanic corrosion, so you can't replace them with a standard valve core.