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Old 01-20-2017, 12:30 PM   #1
Hockeymanc
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Default Tire pressure incorrect on dash?

Hey y'all,

Just traded in my 15' WRX for a 17' limited wagon. After delivery, I noticed that the tire pressure displayed on the dash is way high (40-42 PSI), even though I verified that it's 32 PSI all around manually. I just ignored it for a week since I was getting snow tires anyway.

Fast forward to yesterday, had my snow tires installed by the shop, and the reading is still around 41 PSI. I asked them about it and he said "the pressure is right, just drive it around for a few miles and it'll reset itself," so off I went.

20 miles later, my display is still showing 42 PSI all around. I've once again used my own pressure gauge and verified that it's actually 32.

I can't find anything in the manual, or on this board, about resetting the reading. Is there something special I need to do to get it to re-read correctly?

TIA
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Old 01-20-2017, 12:55 PM   #2
supertoast
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Does it show that pressure when the tires are cold? Physics says tire pressure will increase with temperature (heat due to friction), but how much I don't know. I remember riding in a buddy's Chrysler 200 from the early 2000s and seeing live TPMS data showing about that same pressure. Low 40s PSI.
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Old 01-20-2017, 01:13 PM   #3
drpoop
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I always find it odd that people ask about technical problems here and risk screwing up their car trying to fix it themselves rather than using the freaking warranty the car came with.
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Old 01-20-2017, 04:06 PM   #4
Hockeymanc
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Quote:
Originally Posted by supertoast View Post
Does it show that pressure when the tires are cold? Physics says tire pressure will increase with temperature (heat due to friction), but how much I don't know. I remember riding in a buddy's Chrysler 200 from the early 2000s and seeing live TPMS data showing about that same pressure. Low 40s PSI.
It varies a few PSIs in cold vs warm temps, but the range is like 40-43 PSIs. I don't think it should be off by 7-10 when I've manually confirmed it to be 32.



Quote:
Originally Posted by drpoop View Post
I always find it odd that people ask about technical problems here and risk screwing up their car trying to fix it themselves rather than using the freaking warranty the car came with.
Maybe you're not familiar with other car brands, but many of them come with an option to reset/re-read the tire pressure monitors using the dash computer.

Just asking if this was possible in the 17' Impreza, in case I failed at reading comprehension with the owner's manual.

I find it odd that someone with "dr" in their username doesn't freaking understand the process of basic troubleshooting.
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Old 01-20-2017, 04:44 PM   #5
TrickNipple
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Have you rebooted the ECU? I'd give that a shot before going into the dealer.
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Old 01-24-2017, 06:26 PM   #6
Charlie-III
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Quote:
Originally Posted by supertoast View Post
Does it show that pressure when the tires are cold? Physics says tire pressure will increase with temperature (heat due to friction), but how much I don't know. I remember riding in a buddy's Chrysler 200 from the early 2000s and seeing live TPMS data showing about that same pressure. Low 40s PSI.
A "close value" is air pressure changes by 1PSI per 10*F.
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Old 01-24-2017, 06:44 PM   #7
KC
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Did they reset/match the TPMS sensors to the car? Can you verify they did?

WHen I swap wheels, the car will show the last known TPMS pressures until the new tires are matched.

After that, they should update much more quickly, almost realtime.

--kC
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Old 02-13-2017, 06:05 PM   #8
pheriwinkle
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On the topic of tire pressure--does anyone know how to change the tire pressure display from kpa to psi? I couldn't find it in the manuals nor through playing with the controls.
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Old 02-13-2017, 09:48 PM   #9
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Quote:
Originally Posted by pheriwinkle View Post
On the topic of tire pressure--does anyone know how to change the tire pressure display from kpa to psi? I couldn't find it in the manuals nor through playing with the controls.
Pages 3-39 through 3-42 explains how to do it.

--kC
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Old 02-14-2017, 02:21 AM   #10
CosmoTheCat
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Quote:
Originally Posted by KC View Post
Did they reset/match the TPMS sensors to the car? Can you verify they did?
If the sensors aren't programmed to the car, you should be getting a TPMS light yelling at you. We were told in class that after a rotation (or mount/balance, etc) that we don't need to register the sensors, as they'll figure out who went where after driving for a minute or two.
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Old 02-14-2017, 02:30 AM   #11
drpoop
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Always thought it was retarded that TPMS sensors are usually supposed to be programmed into the correct wheel place... I mean as far as I know most (not all) brands you can rotate the tires without it going insane. So idk why you can't just write all codes.
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Old 02-14-2017, 08:16 AM   #12
KC
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Quote:
Originally Posted by CosmoTheCat View Post
If the sensors aren't programmed to the car, you should be getting a TPMS light yelling at you. We were told in class that after a rotation (or mount/balance, etc) that we don't need to register the sensors, as they'll figure out who went where after driving for a minute or two.
Oh, that's good to know, because many cars sensors have zero clue what corner they're on and just say "My pressure is X and that's from where I was tagged on this corner with a reset tool."

--kC
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Old 02-14-2017, 10:24 AM   #13
Charlie-III
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Quote:
Originally Posted by KC View Post
Oh, that's good to know, because many cars sensors have zero clue what corner they're on and just say "My pressure is X and that's from where I was tagged on this corner with a reset tool."

--kC
That is my interpretation as well. The control unit has 4 or 5 registers, one for each wheel (and maybe the spare). Programming tells the control unit what ID is in what location.
When you rotate tires, the display will be incorrect. Depends on the display/system.
Some just say a pressure is low, some show a picture of the car with a pressure at each location.

The programmer we use has you start at right front wheel, it triggers the sensor and checks it, stores the ID, then you go CW through each corner to get all the ID's. Then you plug into the OBDII port and save the info, even if the ID's don't change, the order the controller sees them affects where hey show up on the car picture.

Some simple systems, no car picture, don't have to have a new sensor programmed, the controller just interrogates the sensors until it finds all the IDs and checks the pressure readings.
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Old 02-14-2017, 03:41 PM   #14
OneWhiteSti10
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Quote:
Originally Posted by Hockeymanc View Post
Hey y'all,

Just traded in my 15' WRX for a 17' limited wagon. After delivery, I noticed that the tire pressure displayed on the dash is way high (40-42 PSI), even though I verified that it's 32 PSI all around manually. I just ignored it for a week since I was getting snow tires anyway.

Fast forward to yesterday, had my snow tires installed by the shop, and the reading is still around 41 PSI. I asked them about it and he said "the pressure is right, just drive it around for a few miles and it'll reset itself," so off I went.

20 miles later, my display is still showing 42 PSI all around. I've once again used my own pressure gauge and verified that it's actually 32.

I can't find anything in the manual, or on this board, about resetting the reading. Is there something special I need to do to get it to re-read correctly?

TIA
Take it to Subaru, they'll fix it for free.i just went in yesterday and they fixed it.
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Old 02-14-2017, 07:17 PM   #15
Charlie-III
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Silver Sleeper Wagon

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Quote:
Originally Posted by OneWhiteSti10 View Post
Take it to Subaru, they'll fix it for free. I just went in yesterday and they fixed it.
Do you know what they did besides "fix it"?
Replace a part?
Program the sensors?
TPMS reflash/update?
Mash buttons on the dash?
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Old 02-16-2017, 12:13 PM   #16
Impreza2121
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Default Agree. What was the repair?

Thanks in advance. Would love to know what the fix was.
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Old 02-17-2017, 04:54 AM   #17
DriveLove
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Default Change kPa to psi

Quote:
Originally Posted by KC View Post
Pages 3-39 through 3-42 explains how to do it.

--kC
Thanks, @KC! It took me so long just to get through the Keyless Fob section! Yikes!
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Old 02-17-2017, 10:56 AM   #18
KC
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Quote:
Originally Posted by DriveLove View Post
Thanks, @KC! It took me so long just to get through the Keyless Fob section! Yikes!
No prob. I know I could have just given the answer, but the instructor habit in me would rather point to where the answer is.

--kC
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