USCRugby

The tire pressure for all my tires except the spare are at 35 PSI. That warning keeps on coming up and it's annoying as hell. I don't want to go into the truck, pull out the spare just to make the annoying warning light go away. Any suggestions?

daryll40

the valve is on the "upside" of the spare. You do have to take your stuff out and open the trunk floor, but you do not have to hassle with removing the tire. I filled mine to 40 pounds about a year ago and it's now down to 36. If you overfill somewhat, you have a long time before having to "top it off" again. Just remember if you have an emergency that requires a long drive after putting on the spare to let a few pounds out. Odds are that won't happen anyway or if you use the spare it will be for a short hop until you can get the situation remedied.

USCRugby

Good advice. I'll try to do this later on today. I hate the warnings!

jmcraney

I don't have any exact knowledge about how the TPMS works, just what I have gleaned from my owners manual. But I think there are some things you need to consider to mitigate the low pressure warnings.

First of all I want to say that I think the TPMS is a very good thing. As I understand it, some version of the TPMS is mandated by NHTSA for all cars and light trucks sold in the USA beginning in 2008. It will save lives and I am very pleased to have it. There will be a learning curve for tire service people and owners alike. And it is certainly more expensive, especially when they damage the sensors when replacing the tires.

Now here is my take on how it works. When you "Reset" the TPMS you establish the pressures in each tire at that time as a Benchmark. I am not sure where the alarm threshold is but for discussion purposes let's say it is minus 4 PSI relative to the benchmark. This means that if each tire was inflated to 33 PSI at the time of reset, then when any tire drops lower than 29 PSI the Low Pressure warning will sound. So, you can operate your tires at any pressure you want to. You just have to inflate them to the pressure you want - you could have one at 25 PSI and another at 29 PSI and the others at 33 PSI and the spare at 40 PSI if you like - before you reset the TPMS.

If you don't have personal knowledge of where the benchmarks are set in your system, and you are having trouble with alarms, then you need to do a reset. The procedure is detailed in your owners manual. Procedures like that have to be followed exactly to get good results.

I did notice that the dealer inflates my spare to 40 PSI, I assume because it is not as easy to access to compensate for long term slow leakage. Daryll40's advice is very good, but here is what you need to do to avoid a pitfall. You need to inflate your spare to the same pressure as your other tires when you reset the TPMS. After you have done the reset then boost the pressure to 40 PSI, then you will have an 11 PSI (assuming 33 PSI is normal/benchmark) leakage margin instead of a 4 PSI margin.

And you need to be especially mindful that "Reset" needs to be done when the tires are cold. This will allow the normal operational pressure drift to be away from the warning threshold. If you do the reset when the tires are hot then they may be very close to the warning threshold when you first start in the morning and just minor under-inflation may cause the low pressure warning.

If you continue to have problems after these considerations then get some help from the pros.

Johnny

A warning comes up on the dash when any one of the tires indicates a pressure of 26psi.

jmcraney

I don't think I worded this part very well and I think it would be better stated as follows:

And you need to be especially mindful that "Reset" needs to be done when the tires are cold. This establishes the "Low Warning" threshold low enough (4 PSI below the cold pressure in my example) that minor under-inflation, later on, will not cause an ambiguous low pressure warning when the car is first driven after it has been sitting still for a long time (overnight).

boxcarfan

omg. lazy.

jmcraney

I am curious to know if you are still having problems with your tire pressure warning system?

I was at the dealership yesterday and talked to the person who is supposed to know and he told me that my understanding of the TPMS was correct. He also told me that the warning thresholds are 15% below the benchmarks that are established at the time of "reset."

The Customer Relations supervisor told me that they have of wave of people coming in for TPMS issues when the weather suddenly turns colder - probably an indication that their TPMS was reset when the tires were hot (my opinion). To mitigate the extra effort required to deal with all those non problems he told me that the dealership is starting to fill all tires with nitrogen. The following link gives some interesting details about why that might be a good idea although when everything is done correctly it is probably not necessary.

http://www.bargaineering.com/article...s-mileage.html

mduffin

Consider having your dealer inflate the tires with nitrogen. Nitrogen molecules are larger than air and as a result less is leaked to the atmosphere. In the climate here, the outside temperature flips between below-freezing to above-freezing frequently in the fall and spring. Each flip seems to sap pressure from the tires when filled with air. Not so with nitrogen. Plus there's little to no moisture in nitrogen which prevents the wheel from rusting inside. The small areas of rust occurring around the tire seat also leads to pressure loss. The rust factor increases with wheel age and can be frustrating if you keep your vehicles a long time.

At the dealer here it costs about $40 per vehicle. All my vehicles now have nitrogen and I've not had any annoying pressure losses since the change. Nitrogen - highly recommended.

jmcraney

If you read the extensive discussion in the link that I provided above you will see that the opinions are quite diverse. Some contributors, with credentials (claimed), say that there is no advantage to using nitrogen. Others attest that it works well. The impression that I got from all the comments was that if you use air, then you need to be sure it is dry. Most but not all air sources are passed through several dryer stages.

$40 seems a little excessive.

I am skeptical. Although I was not having any problems, I have nitrogen in all my tires now, but not at $40. We shall see.

PatsSoxfan

Jeff,

I can tell you from first hand experience that I am quite disappointed with the Nitrogen. They filled my all season tires with Nitrogen back in the spring when I took the snow tires off. Everyhthing was going well (at least I thought) until it started to get cold (down in the 20s and low 30s for morning lows about a month ago). The service manager had told me that I will never have to mess with the tire pressure with Nitrogen. One cold morning a message came up on the instrument panel telling me to check air pressure. Sure enough it was down to 25 or 26 at least on one of the tires. I was cussing to myself. I brought it to the Lexus service and they pressurized them back up to 33 psi. The manager had no good explanation. After that incident I kept a close watch on the pressure and as it got colder outdoors here in the cold Midwest, the tire pressure was once again decreasing. Now I was really getting upset. I again brought it to service and they increased the pressure back up to 33 (it was getting down to 28). To make a long story shot, I am very disappointed in the Nitrogen thing. I am continuing to monitor the pressure daily. So far, it only drops down to 31 or so after the last "fix" when its cold outside. Hey, at least the wind noise issue is solved.

BTW Jeff, I sent you a private message a few days ago. I hope you got it.

sellshomes

On my LS460L there are five (5) psi for the tire pressure, which one is the spare? and how do I know which one is the drive front left, driver front right, etc.?

daryll40

Unfortunately you do not. What I did was make a little chart and tape it to my "airbag warning" on the visor. You'll need to let air out of a tire (or overinflate it) temporarily to see what is what. Once you do it and make your charge, update it when you rotate. This is one "duh" design flaw of the LS. Even GM puts numbers with a tire schematic on the dash board on their upper end vehicles. (Upper end GM vehicle...is that an oxymoron?)

jmcraney

I think this is an excellent approach if you need to (or want to) know this sort of thing. But, for those fancy GM cars with the absolute indicators this low tech mapping strategy is also appropriate because even though they have the illusion of telling exactly what pressure is coming from what location it is the same old problem after rotation, unless the display is resynchronized. So anyone with an absolute indicating display, you need to insure it is indicating correctly if that feature is important to you and you will be basing decisions on that information.

daryll40

I am not sure that's right...I don't think the GM cars need resynched after rotation.