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Tire air pressure - is the dealer just trying to inflate my bill?

Recently purchased a new (used) car. The first cold day, my tire pressure warning light came on (I had checked pressure when I purchased the car and all tires had 30 psi as listed on the door panel).

I checked the pressure and it was 30 psi on all 4 tires. Went to work, dropped the spare to check it; odd, it was 29.5 psi. I checked the door panel and manual both state - 30psi for all 5 tires.

I phoned the service dept for the dealer where I bought the car - the service person told me “yeah, this happens with winter coming on” - so I told him the pressure was correct - he then said “we always change the pressure monitor setting to a higher pressure because the tires will last longer and the car will ride better”. HUH?? I expressed my confusion that the dealer was altering factory settings and ask what could be done to fix the issue. He said to inflate my tires to 35 pounds or come into the service department and they could reset the tire monitor to the factory recommendation of 30 psi.

Now I’m confused and a little worried.

Should I over inflate my tires as the dealership suggests? will my tires last longer and my car ride better? or

Is the service department doing this so my tires will wear out quicker and I’ll spend more money at the dealership?

Please help!! I’ve got a LOT of PRESSURE to get the correct answer.

Someone more knowledgeable than I will have to comment on the dealer’s claim that they up the pressure monitor setting. It sounds a bit screwy to me.

But I can say that running the tires 5 lb. over won’t be a problem and it will help some things. It will likely improve gas mileage by a tiny amount, though probably not enough to notice. It probably will eke a few more miles out of the tires. As for how it rides and handles - give it a whirl. It can go differently on different cars.

In general you are right about following the door pillar. But you can play with the pressure some to see what you’re happy with (even you can even notice). The real rule about “overinflation” is just to never exceed the maximum cold pressure given on the side of the tire. Under inflation is just bad all around - so don’t go below 30 cold.

Oh … and the thing about winter is right too if you live in a place that gets winter. Pressure falls with temperature.

The service dept answer sounds a little fishy to me. I’d ask an independent mechanic about this. You can increase the pressure to 35 psi and this may be advisable if you’re carrying a heavy load but I can’t imagine why the service dept would change the factory setting.

General philosophy is to stick with the tire pressure recommended. So it sounds like the monitor has some problems. If you can get them to fix it great, I have never had a monitor system, so if it was expensive to replace I would consider a small piece of electrical tape for the dash, and keeping a tire gauge handy. The over inflation may cause the center of the tire to wear out more quickly, reduce handling and traction but increase gas mileage.

What year is the Lexus? My wife’s 2006 Toyota Sienna has a warning light for the TPMS. The Tire Pressure Monitoring System (TPMS) on the Toyota uses the ABS system to detect a tire that’s low. I believe the principle is that a tire with a low pressure will rotate at a different speed than the other tires and the ABS system will detect this. The van has a slow leak in the right front. The TPMS light did not come on with 3 tires at 34 psi and the leaking tire at 27 psi. The only time the light has come on was a few days after a tire rotation.

2007 and newer Toyotas measure the tire pressure directly with a sensor in each tire. Sometimes a sensor will go bad and need to be replaced.

Either TPMS system has to be reset after a tire rotation or tire replacement. The directions will be in the User’s Manual. There’s no substitue for checking the tire pressure on a regular basis with a dial-type gauge.

Ed B.

Hot air expands and cold air contracts. In my experience you do need to add air once cold weather sets in. 1/2 pound is nothing to worry about. Just use a (Good) tire guage and forget about that computer…

Waterboy has covered it well. I will only add that it is not unusual for a dealer to suggest that on cars with sensors, but frankly they are just trying to get you off their back because it is easier to for them.

Five PSI should not cause much of a problem if any. Some small changes in tyre life handling and ride. It might be the easiest way out for you also. However if it were my car, I would want to have them give me documentation from the manufacturer that says their fix is approved by the manufacturer.

The reason you have those sensors is for safety. I would push them on it. You have a right to expect them to get it right. At the minimum I would want something in writing from the manufacturer.

Check the air pressure of the spare…valve sensors are on all tires.

It seems the OP is saying these systems can be programed as far as when they say a tires pressure is low? Not saying this option does not exist but I have never been asked to change this value and never saw the field on a scanner.

Personally, I’d go with 30 PSI and have them fix the monitor. (Even if you decide to experiment with higher pressures, I’d still have them fix the monitor, as the tire isn’t unsafe until it drops below 30 PSI.)

I have a friend who has this problem, but I can’t remember which car it is. He has a Toyota Prius and a Ford Escape Hybrid. The low pressure warning light came on one cold night on our way back from a band rehearsal. He says that it happens in cold weather and he just ignores the light. He checks his tires regularly with a gauge.

I was driving one of our institution’s Ford Windstar vans–it was either a 2001 or 2002 back from a conference. At any rate, on a milled portion of the interstate, the low tire pressure light went on. I couldn’t stop because there was one lane of traffic each way. When we finally did get out of the construction zone I stopped for a cup of coffee. Fortunately, the manual was in the glove compartment. I read the directions and turned the light off and it stayed off for the last 200 miles of the trip. I think that the vibration from the milled pavement turned the light on.

Frankly, I think these tire pressure lights are more trouble than they are worth, but I check my tires every other week with a tire gauge.

On the other hand, an extra 5 psi might lead to tread separation and shorten the live of the shocks/struts.

Personally, I’d go with 30 PSI and have them fix the monitor.

Me too.

Have you checked your owners’ Manual? I have a Scion, also a Toyota product, and a few years ago Toyota was using the wheel speed sensors for its TPMS readings. My owners’ manual has a procedure for “resetting” the lights as well as a protocol for “reinitializing” the system, which establishes new baselines for the system. The protocol for reinitializing is in an entirely different section of the owners’ manual, oddly enough. Yours may have such a protocol also.

Two points here.
One is that the person you were conversing with at the dealer was more than likely a service writer. Very few of these people have any mechanical abilities to speak of.

Two is that you’re assuming your tire pressure gauge is correct.

It used to be that manufacturer recommended tire pressures were biased low, because they wanted you to have a comfortable ride, and didn’t give a [dung. coprolite. turd. ****] how long the tires lasted or what kind of gas mileage you get. Used car dealers were even worse, setting the cars on their lot dangerously low.

I keep mine about 35.

already covered this in my post

fortunately the monitor system isn’t broken, rather has the wrong setting in the computer (according to the dealer). the dealership says they can change the setting in the computer. They reset the monitor to the factory recommended setting at no charge.

Thanks - good suggestion.

my lexus is 2008. I had a similar problem with my '06 tundra - in that situation, the spare tire had slowly lost air pressure. After I corrected the pressure in my spare, the light went out.

Thanks, I do check my tire pressure about once a month. Likewise I have heard the sensors can go bad and cost around $80 to replace (OUCH).