Snow tires & tire pressure monitoring system.

[Cougar Vibe]

Last night I put my snow tires on the Vibe, took it out for spin and then torque'd down the lug nuts again. Anyway, I suspected that the tire pressure would be low and sure enough, all four tires were (~25 psi). My question is: Why didn't my Vibe's tire pressure monitor alert me to a change in pressure? My all season tires were 35psi in the front and 32 in the rear; that's 7-10 psi more than my snow tires. Is it because all four of my snow tires were the same psi (~25), and the system only alerts if there is a significant difference in one of the four tires (as compared to the others)? Thanks for any comments...Cougar VibePS: There's a Woot-off going on, if you're interested. No BOC yet!!!

[MailGuy!]

I may be wrong here. But I read something that said tire pressure monitors can go haywire by simply using non oem tires and will never work right if you dropped a wheel size for snows. my .02.

[tnpartsguy]

the TPM on the Vibe is odd anyway. It does not use discreet RF sensors like every other GM product; it uses the wheel speed sensors from the ABS system. Thats why you must drive at least 60 miles after hitting the 'set' button to have the system function at all. It takes that long for the system to properly calibrate (it looks for minute differences in wheel speed when going straight, btw), because it only measures wheel speeds when going directly straightline (it uses a steering wheel position sensor to know when it's going straight).Is it a good system? No it's about like our version of On*Star, it's there and it works....sorta.

[LUVROK]

I had this discussion two nights ago with the sales manager where I purchase my new snow tires. I told the manager the wheel speed sensors were used and he didn't believe me. Sure enough, there were no RF sensors as part of the valves stems so he quickly clicked a link on his computer and within seconds had a print out of the tire pressure monitoring system that is quite in depth.I will scan it and post a copy.As far as answerign your question about why the monitoring system didn't go off is that I don't think it will go off if all tires are at the same pressure. I believe it looks for a significant difference in one tire as seen by the wheel speed sensor from a smaller diameter tire due to low air pressure. A stiff tire like a run flat may never show your system it's low on air. I don't believe in run flats anyway. I blew out a 37" mud tire on I-90 and my rig handled just fine, no roll over, not even close...just a bit of a bump bump bump.

[keithvibe]

I know when I purchaced my Vibe that the tire presure monitoring system was not activated. Read up, in your owners manual, I beleive it mentions something like press the button when the tires are cold and at a stop then drive about 50miles on one trip to calebrate the system. I guess so it knows the difference between a cold tire and a hot tire. I may be wrong on this it's been a few weeks since I have opened up the owners manual.

[mikey00]

The TPM on the Vibe works by checking for a difference in tire rotations. If all 4 tires loose the same amount of pressure there is no difference.