Confused about tpms
11-10-2007, 05:22 AM
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Confused about tpms
With 16 miles on my 08 unlimited I installed the new wheels and tires. I did not know the jeep even had the tire pressure sensors on the stock wheels. I guess they are the valve stems themselves. No problems at all, until yesterday the low tire pressure light came on and stayed on all day. I discovered there was no way to disable, and decided i would live with it.
Now the light is off. Why if the sensors are gone is the light off, wouldnt it be on all the time. I still have the stock spare on the back, I heard that is monitored also. Anyone else experience this.
Now the light is off. Why if the sensors are gone is the light off, wouldnt it be on all the time. I still have the stock spare on the back, I heard that is monitored also. Anyone else experience this.
11-10-2007, 07:13 AM
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You have air in your tires.....duhh...you say. I bet that it was cold in the morning and warmed up during the day. If so, you probably just need to air them up a little. It's typical.
Cold=air contracts, tire psi goes down
Hot = air expands, tire psi goes up
The first day that it dipped into the 30's here in GA, the light on my wife's Tahoe came own. The four tires had been showing about 32 psi all summer, but dipped to like 26-27 psi in the colder weather. Ran it up to about 36psi and no more problems.
Cold=air contracts, tire psi goes down
Hot = air expands, tire psi goes up
The first day that it dipped into the 30's here in GA, the light on my wife's Tahoe came own. The four tires had been showing about 32 psi all summer, but dipped to like 26-27 psi in the colder weather. Ran it up to about 36psi and no more problems.
11-10-2007, 07:45 AM
#3
JK Junkie
to test this, I let the air out of my spare and kept my other wheels at 35 PSI...
the light did not turn on.. I was a little confused.. let some air out of another tire and the light came on..
I dont think the spare is monitored..
Do you happen to have the TPMS sensors inside the JK somewhere?? Im pretty sure if you do It will keep the light off because they all have the same pressure.
the light did not turn on.. I was a little confused.. let some air out of another tire and the light came on..
I dont think the spare is monitored..
Do you happen to have the TPMS sensors inside the JK somewhere?? Im pretty sure if you do It will keep the light off because they all have the same pressure.
11-10-2007, 03:22 PM
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With 16 miles on my 08 unlimited I installed the new wheels and tires. I did not know the jeep even had the tire pressure sensors on the stock wheels. I guess they are the valve stems themselves. No problems at all, until yesterday the low tire pressure light came on and stayed on all day. I discovered there was no way to disable, and decided i would live with it.
Now the light is off. Why if the sensors are gone is the light off, wouldnt it be on all the time. I still have the stock spare on the back, I heard that is monitored also. Anyone else experience this.
Now the light is off. Why if the sensors are gone is the light off, wouldnt it be on all the time. I still have the stock spare on the back, I heard that is monitored also. Anyone else experience this.
Usually, when you install wheels/tires that don't have the sensors in them the dash light will illuminate indefinitely. I have rather extensive experience with this and I've never seen a vehicle turn the light off. I'd consider myself lucky if it stays that way!
11-10-2007, 06:48 PM
#5
to test this, I let the air out of my spare and kept my other wheels at 35 PSI...
the light did not turn on.. I was a little confused.. let some air out of another tire and the light came on..
I dont think the spare is monitored..
Do you happen to have the TPMS sensors inside the JK somewhere?? Im pretty sure if you do It will keep the light off because they all have the same pressure.
the light did not turn on.. I was a little confused.. let some air out of another tire and the light came on..
I dont think the spare is monitored..
Do you happen to have the TPMS sensors inside the JK somewhere?? Im pretty sure if you do It will keep the light off because they all have the same pressure.
The spare on my Unlimited Sahara has the TPS as I would have thought. If you had a flat or decide on the 5 tire rotation your TPS light would pop up with the spare if it was mounted with no TPS monitor. You will be able to tell if your spare has a sensor by looking at the valve stem. It will be a light gray cap and stem.
I have had experience with my Dodge Magnum RT with theTPS light as I tried pulling the fuse....but the car went into limp home mode (no power). I would imagine the Jeep would work very similar. You would be very lucky to have your light go out with no TPS in your wheels.
Last edited by RevyJKU08; 11-10-2007 at 06:51 PM.
11-10-2007, 07:41 PM
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The Jeep's TPMS sensors are absolute tire pressure sensors and have both pressure sensors and accelerometers in them. A pressure "inbalance" does not trigger the system but an absolute pressure on any tire below the threshold triggers the system. If you air down all your tires equally, the system will still trigger.
The accelerometers in the sensors are used to detect tire rotation. Basically the sensor sleeps until rotation is detected. Once that happens, the sensor wakes up and transmits it's pressure data to the monitoring system. Unless you roll sideways off a rock, the spare is always sleeping.
I haven't figured out how the monitoring system is programmed yet, but my theory is it knows the serial numbers of five sensors--the four on the ground and the spare. As long as the four of them that are reporting rotation report OK pressures, the system will not trigger.
Battery life is supposed to be 3 to 7 years. The valve stem forms the antenna for the transmitter. They can share a radio receiver with the remote keyless entry system and / or transponder key, and I suspect they do on the Jeep to keep costs down. The receiver for the Jeep's RKE is a 315MHz ASK receiver--I did verify that. The TPMS sensors emit a 315MHz ASK transmission telling the RKE to stop listening for the key fob and listen for a pressure transmission. Each pressure sensor then sends a series of 315MHz FSK modulated bursts with the relevant tire pressure data. The sensors act independently of each other and use random transmission timing to prevent collisions.
The sensors have a provision for using an electromagnet or 125kHz transmitter in each wheel well to allow the monitoring system to learn which sensor is in which position on the vehicle. The Jeep does not use the capability. Instead, I suspect, the dealer puts the computer in to a learn mode and takes a manual swipe at each wheel with a magnet or 125kHz transmitter to tell the sensors to transmit immediately without waiting for tire rotation.
My suggestions to Chrysler to make the system useful:
1) allow a programmable trigger threshold in 4LO. The difference between 15psi and 10psi could be critical on the trail.
2) monitor the spare--the sensor is already there and it's the tire most likely to be flat.
The TPMS (of not just your own vehicle) is ripe for hacking opportunities.
-Glen
The accelerometers in the sensors are used to detect tire rotation. Basically the sensor sleeps until rotation is detected. Once that happens, the sensor wakes up and transmits it's pressure data to the monitoring system. Unless you roll sideways off a rock, the spare is always sleeping.
I haven't figured out how the monitoring system is programmed yet, but my theory is it knows the serial numbers of five sensors--the four on the ground and the spare. As long as the four of them that are reporting rotation report OK pressures, the system will not trigger.
Battery life is supposed to be 3 to 7 years. The valve stem forms the antenna for the transmitter. They can share a radio receiver with the remote keyless entry system and / or transponder key, and I suspect they do on the Jeep to keep costs down. The receiver for the Jeep's RKE is a 315MHz ASK receiver--I did verify that. The TPMS sensors emit a 315MHz ASK transmission telling the RKE to stop listening for the key fob and listen for a pressure transmission. Each pressure sensor then sends a series of 315MHz FSK modulated bursts with the relevant tire pressure data. The sensors act independently of each other and use random transmission timing to prevent collisions.
The sensors have a provision for using an electromagnet or 125kHz transmitter in each wheel well to allow the monitoring system to learn which sensor is in which position on the vehicle. The Jeep does not use the capability. Instead, I suspect, the dealer puts the computer in to a learn mode and takes a manual swipe at each wheel with a magnet or 125kHz transmitter to tell the sensors to transmit immediately without waiting for tire rotation.
My suggestions to Chrysler to make the system useful:
1) allow a programmable trigger threshold in 4LO. The difference between 15psi and 10psi could be critical on the trail.
2) monitor the spare--the sensor is already there and it's the tire most likely to be flat.
The TPMS (of not just your own vehicle) is ripe for hacking opportunities.
-Glen