Tire Pressure Warning Light
11-23-2010 | 03:19 PM
#22
JK Freak
Joined: Feb 2010
Posts: 793
Likes: 1
From: Seattle, WA
Originally Posted by AZJeeper
Yup. The 2008 to 2011 Owners Manual says "A low spare tire will not cause the "Tire Pressure Monitoring Telltale Light" to illuminate or the chime to sound."
Yet it does. This is why I think it triggers the system:
There are accelerometers embedded in the sensor that detect motion and "power up" the TPMS. I suspect what is happening is a series of bumps is enough to turn them on, and since this is a "dumb" system (doesn't detect WHICH wheel, just that one is low), the sensor fires off a "I'm low on pressure" signal. Once a sensor has reported low pressure, I believe THAT sensor has to report good pressure. That's why it took 30 miles to finally turn off the alert once the spare was inflated - the Jeep had to be driven under the right conditions to trigger the spare sensor.
The interesting thing is the system is expecting 4 sensors to contribute, so if the spare is removed the system does not go off, assuming the 4 mounted ones are at the right pressure and the spare didn't already trigger the alert. That's probably what the owner's manual is trying to say.
That is how it works on my JK. I've tried several scenarios and it is consistent with the explanation above (OK. I was bored and needed something to do).
11-23-2010 | 06:59 PM
#24
JK Enthusiast
Joined: Nov 2010
Posts: 160
Likes: 0
From: Omaha, NE
2010 tpms tripped this afternoon (33 degrees out) due to the cold air. I checked the pressure after a few hours at home and it was 33 psi. On a 35 psi system, one wouldnt think that it would go off at just 2psi diff. Bumped up to 38 all 5 tires (spare last) with the engine on and light turned off once 5th and final was up to snuff. Wife was watching the light. Just bump up the pressure a bit and that should fix it.
11-25-2010 | 11:23 AM
#26
JK Enthusiast
Joined: Sep 2010
Posts: 247
Likes: 0
From: Galesburg, Illinois / Menifee, California
TPM......WTF? This is my first Jeep.....
I have an 08 JKU and as far as I can tell no TPM system however, the TPM light is now on. I have flipped through the two digi dash guages and no TPM. Am I missing something? Do I have TPM's and not know it?? It is cold out and plan to check/air the tires to hopefully fix but you would think it would have the tire's pressure in the display if I do in fact have TPM's. Advice/answers/knowledge????
11-25-2010 | 06:20 PM
#28
JK Freak
Joined: Feb 2010
Posts: 793
Likes: 1
From: Seattle, WA
I have an 08 JKU and as far as I can tell no TPM system however, the TPM light is now on. I have flipped through the two digi dash guages and no TPM. Am I missing something? Do I have TPM's and not know it?? It is cold out and plan to check/air the tires to hopefully fix but you would think it would have the tire's pressure in the display if I do in fact have TPM's. Advice/answers/knowledge????
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11-26-2010 | 08:38 AM
#29
JK Freak
Joined: Nov 2010
Posts: 982
Likes: 0
From: Calgary, Alberta
37 seems really high for a 32" tire. But I will try the 35 psi, and hope for the best.
11-26-2010 | 10:50 AM
#30
JK Freak
Joined: Feb 2010
Posts: 793
Likes: 1
From: Seattle, WA
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