Can I check tire pressure through MMI for my 2017 A4?
07-21-2017, 08:25 AM
#2
AudiWorld Super User
No, the system in the 2017 A4 measures relative deviation from the set tire pressure and simply alerts if the pressure deviates by about 20% from the set conditions. There are no sensors in the wheels to measure absolute pressure. The system uses the wheel speed sensors and digital signal processing to analyze oscillations in the wheel assembly that are sensitive to changes in tire pressure and can detect if the tire pressure deviates from normal.
07-21-2017, 08:49 AM
#4
AudiWorld Super User
The recommended pressures are documented in the owner's manual for different load scenarios and tires. If you are just driving around by yourself with a mostly empty trunk and occasional passengers, then you should use the normal load pressure from the owner's manual. It's lower than what's on the door sticker. The pressure on the door sticker assuming you are in the USA only lists the max load recommended pressure which is meant for when the car is fully loaded with passengers and luggage. In other parts of the world, the door sticker lists all the recommended tire pressures, so you don't have to go fish for it in the user manual, but the US DOT figured Americans will get confused with too many numbers ;-).
07-21-2017, 12:05 PM
#6
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So, I got a tire pressure warning, but then I set the tires in the MMI without filling the tires. Now the warning is gone.
Think I'm good to go?
07-21-2017, 12:17 PM
#7
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Did you check each tire with a pressure gauge? If so and they all were within the recommended pressure range, then you are good.
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07-21-2017, 12:54 PM
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07-21-2017, 01:21 PM
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Let me try to explain this in simple terms. Let's say you checked your tire pressure and they are all at 36 PSI. You then go into the MMI and reset the TPMS. Now the system learns for the next 20 minutes or so how your car "feels" and "drives" with the tire pressure at 36 PSI. Later, if your tire pressure falls to about 28 PSI (20% below what it should be), the system detects that and alerts you, because your car "feels" and "drives" differently with the lower tire pressure.
Similarly if you set all your tires to 40 PSI, then reset the system. It will alert you when the pressure falls to about 32 PSI.
So first of all, there is a 20% margin that it allows for the tire pressure to fall before you get any alerts and secondly it doesn't know the actual tire pressure.
Here's some additional reading on indirect TPMS: https://en.wikipedia.org/wiki/Tire-p...#Indirect_TPMS
Last edited by superswiss; 07-21-2017 at 01:29 PM.
07-21-2017, 02:36 PM
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They may or may not be good to go. You have to measure the tire pressure old school when they are cold or haven't been driven for at least 3 hours. Once you verified that all 4 tires have the correct pressure, then you go into the MMI and reset the TPMS. This tells the system that you have checked all 4 tires and that they are the desired pressure. It then stores the current reference parameters in the system and starts monitoring for deviations. This is what I meant with the system being relative. The system doesn't know the actual tire pressure. It simply measures a bunch of oscillations and frequencies and associates them with the correct tire pressure based on when you told it that you checked the tire pressure last.
Let me try to explain this in simple terms. Let's say you checked your tire pressure and they are all at 36 PSI. You then go into the MMI and reset the TPMS. Now the system learns for the next 20 minutes or so how your car "feels" and "drives" with the tire pressure at 36 PSI. Later, if your tire pressure falls to about 28 PSI (20% below what it should be), the system detects that and alerts you, because your car "feels" and "drives" differently with the lower tire pressure.
Similarly if you set all your tires to 40 PSI, then reset the system. It will alert you when the pressure falls to about 32 PSI.
So first of all, there is a 20% margin that it allows for the tire pressure to fall before you get any alerts and secondly it doesn't know the actual tire pressure.
Here's some additional reading on indirect TPMS: https://en.wikipedia.org/wiki/Tire-p...#Indirect_TPMS
Let me try to explain this in simple terms. Let's say you checked your tire pressure and they are all at 36 PSI. You then go into the MMI and reset the TPMS. Now the system learns for the next 20 minutes or so how your car "feels" and "drives" with the tire pressure at 36 PSI. Later, if your tire pressure falls to about 28 PSI (20% below what it should be), the system detects that and alerts you, because your car "feels" and "drives" differently with the lower tire pressure.
Similarly if you set all your tires to 40 PSI, then reset the system. It will alert you when the pressure falls to about 32 PSI.
So first of all, there is a 20% margin that it allows for the tire pressure to fall before you get any alerts and secondly it doesn't know the actual tire pressure.
Here's some additional reading on indirect TPMS: https://en.wikipedia.org/wiki/Tire-p...#Indirect_TPMS