Tire Pressure Warning Sensor

[zeroyon]

Hi, I just replaced my front tires at 29k, rears are still fine and both are the 18in summer version. The fronts were actually fine in the center, but both the inner/outer areas were worn, which indicates to me that the tires were underinflated. The pressure signal never came on while I've had the car and I understand the system is designed to indicate faults, turn on the maintenance light, and not indicate which tire it is to force users to double check all tires while you're at it.

Now, with that said, wondering if anyone has had this problem? I saw a TSIB for the tire pressure sensor, but not sure if it's related.

Let me know your thoughts.

[bartkat]

It takes 4 PSI diff to set off the alarm. Were you checking your tire pressure? What PSI were you running?

[zeroyon]

Thanks, good point. When I checked them, they were right at 30psi. It's a bit odd to me that the fronts require a lower pressure than the rear tires, but perhaps I'm missing something.

[bartkat]

Yeah 30 is underinflated. The warning is supposed to go off at 4 PSI difference but when I had a leak in a rear tire it took a lot more before the warning showed. I try to check pressures at least once a month or when there has been a major change in ambient temperature. For every 10 degrees F change in the weather tire pressure will change by 1 PSI.

[zeroyon]

Thanks a lot. Good tip.

[paradigm]

to add to the above...as i found out after getting new TPMS with new wheels...

the warning does not go off until you drive for something like 20+ minutes. i had the new sensors (still not programmed to my ECU) and it took a few weeks before the sensors were detected as missing...simply because i drive mostly in town for now and had not been on the road long enough to trigger the alarm.

[IS250_rookie]

Yeah def keep a good tire guage(one of those clock-like ones, not the cheap pen-like) in the car and check once in a while. My guess for the tire pressure difference is that the car is rear wheel drive and IS250/350 have wider tires in the rear so they need more pressure to compensate for the larger area. Then it brings me to a question, why is AWD 35/38, if the tires are the same size? Is it because it's rear-biased and puts more stress on the rear tires or were the Lexus engineers too lazy to replace the sticker?

[bartkat]

The front tires are also doing the steering plus it's expected you may carry items in your trunk so the rear tire need extra PSI for load carrying.

[mr_raider]

Yeah def keep a good tire guage(one of those clock-like ones, not the cheap pen-like) in the car and check once in a while. My guess for the tire pressure difference is that the car is rear wheel drive and IS250/350 have wider tires in the rear so they need more pressure to compensate for the larger area. Then it brings me to a question, why is AWD 35/38, if the tires are the same size? Is it because it's rear-biased and puts more stress on the rear tires or were the Lexus engineers too lazy to replace the sticker?

Bah.... I run all four wheels at 36. Simpler that way. My gauge doesn't have marks for odd number.