On my wife’s car, we were caught off guard once too, when the low tire pressure warning turned out to be the spare. Her car is a 2008 Toyota RAV4. Now it’s happened so often that whenever the light goes on the first thing we suspect is the spare.
It is called the “girlfriend” school of engineering. It will only tell you that something is wrong and you need to do something about it right away. It just won’t tell you what it is or how to fix it.
Are we going to go through a rehash of the dauerbach “check engine light” thread? There’s a limit to what diagnostic systems can do. Just like if your shoulder hurts, you need a doctor to tell you your rotator cuff is torn.
A few months back my wife told me a warning light came on in her car, immediately causing concern.
I asked her what it was and she said “I don’t know…it looks like a little crown.”
After a bit of thought I figured it out, glanced at the tires and they looked fine (the way we used to do it before TPS systems) and was relieved.
When I went to refill them a few days later I couldn’t get the “crown” light to go out. Upon closer inspection, I realized that the doorframe sticker had different numbers from the tire sidewall–I had inflated them to the 35psi rated pressure, but the doorframe sticker had 32psi front and 30psi rear.
I discovered when getting new tires that while, indeed, the rear left was often low and the light would sometimes go out after I filled it (and sometimes not) that the actual sensor was also a problem. Dry rotted out or something? Not sure. I was tired. But I did find out that I could replace the tire without a new sensor, although I keep reminding myself to go get that sensor replaced. I was just out of cash that day. $600 for tires and $400 for groceries because I get my tires at Costco and went on a deep replenish of the pantry shopping trip while I waited…the extra money for the sensor just wasn’t in the budget that day.
Now I just have to remember to keep an actual eye on that tire AND tell people the light’s on and don’t worry about it when they borrow my car.
I’m lucky that my car (Mini Cooper) points to which tire(s) is low. I don’t think the spare is monitored, though. It is a quirky system that I have gotten used to after four years.
It annoys me that my car doesn’t do this. It has the sensors. It has a little LCD display screen to show me various things. In fact the same screen shows a giant “low pressure” icon when a tire is low – why not show me which tire is causing the problem? It shows a little diagram of the car to tell me which door is ajar so it’s not as though they can’t do this.
The Fella’s Mini Cooper has that light and it was lit up. I asked–“why do you have an idiot light that looks like a butt?” That light makes NO sense!
Mate of mine has a brand new soccer dad Porsche with a similar problem. Seems that the system is hypersensitive, and only “approves” too narrow a range of pressures, so it can be triggered by a hot day and a long drive. And just fixing the pressure at the petrol station doesn’t turn the light off. You have to take it to the dealership. You’d think the Germans would have done a better job of this.
In at least one of my cars, after fixing the pressure you have to reset the light by holding in a button inside the glove box for 5 seconds.
And then you’d be asking why the dashboard has a “check doughnut” light.
You just can’t win. 
Porsche did a great job of ensuring that those who buy their vehicles and inflate their own tires will have to return to the dealership regularly, where they can be subjected to the high-pressure sales pitch for extra services. Just like BMW and their dealer-only reset of the oil change indicator, for owners who changed their own oil, from several years ago…
The shops says the spare in a 2014 Subaru Legacy doesn’t have a sensor. We’ll see what they say when I pick it up this afternoon.
Apparently the sensors on a Legacy are more sensitive than my tire gauge. 1-2 lbs of extra air per tire turned the light off.
Something similar happened to me. A dashboard light I didn’t recognize came on, the car didn’t have anything obviously wrong with it, but out of worry and frustration I eventually took it to a garage.
Mechanic: I hooked it up to our analyzing computer and I know what’s wrong.
Me: What is it?
Mechanic: It’s your rear spoiler.
Me: But I don’t have a rear spoiler.
Mechanic: That’s what it’s saying. You elected not to purchase it.
Me: So how is it showing up on my dashboard?
Mechanic: Each part of your car communicates independently with the car’s electronic system, which controls the dashboard lights. The spoiler is calling from the dealership: it’s very disappointed you didn’t choose it as an option and would like you to reconsider.
Me: Reconsider? It cost almost a thousand dollars, and looked really stupid. No I won’t reconsider. I told that to the salesman. How will you shut the light off?
Mechanic: The spoiler says you had a bad salesman who was bad at selling things. It says it can’t function properly on a shelf in a warehouse and as long as it has to it will keep calling your car and the light will stay on.
Me: That’s ridiculous. If you can’t disconnect just that one light I’ll just ignore it until it burns out.
Mechanic: The spoiler says it won’t submit to your threats. It says two can play that game.
Me: What?
Mechanic: I’m just the messenger, man. But the spoiler says it’s been talking to your brakes.
When the tire light came on just after a routine dealer visit and tire rotation – it’s a pretty new car – I was a little upset. Checking the manual, I found out that after tire rotation, the indicator must be reset. When I did that, the light went away.
I guess the mechanic hadn’t read the manual. Wonder what else he forgot.
But it IS a picture of a tire!
(Viewed from behind, after you run over a nail and have a seriously flat tire.)
My Rogue will display the pressure of each tire. One cold day, it was flashing warning! warning! warning!
So I stopped and filled the tires myself. Color me surprised when the car honked for each tire once I reached the proper pressure! At first I didn’t even notice - I was at a gas station and thought someone else had honked.
Yum, a Krispy Kreme alert light . . .
Nah, it’s definitely a “!CHECK HORSESHOE IMMEDIATELY!”
https://cdn.patchcdn.com/users/21854731/2013/12/T800x600/2b48eb3cd89fedfa9efbcee9c24a4a27.jpg
