For reasons having to do with our Larval Engineer needing transportation, we just bought a Subaru Forester for us. While chewing through the 540 page Owners Manual, I discovered that, although the tire pressure monitoring system knows all five pressures, it can’t / won’t display them on the dashboard’s fancy LCD panel.
All four road tires had about the same pressure:
Yes, I cross-checked two other gauges, Just To Make Sure.
That’s 7 or 8 psi over the spec found on the door frame placard: 30 psi front, 29 psi rear. The tire sidewalls implore you to never inflate them over 40 psi while seating the beads, although the absolute max rating of 51 psi at max load says they’re not really overstuffed.
The doughnut spare tire should have 60 psi and carried 64 psi:
Now, I’ve never had a cold tire gain pressure between checks (other than when the weather heats up), so I tend to run ’em on the high side of the recommended range. In this case, I left the spare alone and vented the road tires to 30 psi to see how it rides. If all goes well, then maybe I’ll puff ’em up a bit.
It’s time to check the fluid levels to see what could possibly go wrong under the hood…
The Smell of Molten Projects in the Morning 
Comments
18 responses to “New Subaru Forester: Tire Pressure Check”
The TPMS is now a requirement here in the US, but it’s probably just a bolt-on that’s added on vehicles made/shipped here, and not integrated with any other systems. There’s also the issue that, at Subaru, the various divisions don’t really talk to each other, but their products are “integrated” into a single assembly.
The interface from the TPMS receiver box could be two bits: “I’m alive” and “Ding!”
But if the receiver goes directly to the Main Box, then it’s just a simple matter of firmware to add pressures to the cute four-wheel-drive cartoon they already have, right?
Uh, whoops …
A couple comments:
1) High pressure could be due to incomplete pre-delivery prep. At factory, tires are mounted/seated to wheels by means of sudden burst of high pressure air blown thru the gap between tire bead & wheel rim. This, plus the fact that tires are less likely to develop flat spots while sitting on dealer lot COULD explain the above-spec pressure you found.
2) Most likely cause is that dealer technicians believe they know more about proper pressure than “factory” engineers.
The TPMS on my new Mazda requires, per Owners Manual, intervention by owner if pressures are significantly changed. I suggest searching manual for this info. Don’t be surprised if you don’t find the needed info under TPMS. After two or three “Refer to page xx” you may find it.
Suffice it to say that the car was not prepped; I installed some accessories directly from their factory-sealed boxes. Don’t get me started, you know what I’m like…
It seems I’m the first person to ever ask for the parts that got replaced by the options: I now have a lifetime supply of spare mirrors, floor mats, and suchlike.
As nearly as I can tell, the TPMS waits for a few miles to see how things are going before it kvetches, unless there’s a total pressure loss. Blowing off 20% doesn’t seem to have bothered it in the least; I’m tempted to deflate a tire (and not drive on it!) to discover the actual “severe low pressure threshold”.
Subaru has a PDF version of the manual, split into 21 “convenient” files ranging from 37 kB to 33 MB. I mashed them into one hulking and easily searchable lump; a copy now lives in my Kindle Fire for under-the-car reference.
Same guy as the post below, I work at a Subaru dealer. Subaru ships their cars with 50psi in the tires. On the “PDI” or pre-delivery inspection, we commonly let the air out to 37psi. The accessories that were in the car, well, Subaru expects us to install those for free with the PDI where they used to pay us for them. Some techs might not know this new process where the accessories in the car need to be installed for no additional labor. Usually its nothing big, maybe the tech just didnt check in the trunk. :)
Well, that sure keeps ’em from developing flat spots all the way across the Pacific! Hokey smokes, Rocky…
Yeah, but the salesman didn’t catch the missing splash guards, either, and I’ll fault him for that… there’s supposed to be a punch list for that stuff!
We have a 2012 Forester, and I just put 4800 miles on it over a couple of weeks. I’ve had to learn the TPMS system after Julie got a warning when she started a road trip last October. (Cost an 80 mile detour…). Forgot a bunch of it already, but here’s what I know. Had a pressure warning flicker after 2100 miles I had overinflated 2PSI before leaving, but the roads were really rough. Not sure of the effect this has on inflation. I rechecked 600 miles later before heading home and had no tire issues. Don’t want to talk about the weather en route. [wince]
1) The Forester is pretty serious about the odd tire pressures. Ed Neidermeyer (of curbside classics dot com) has/had a 2003, and it’s the same. I suspect it has to do with the suspension setup.
2) The system consists of a sensor, a centrifugal/magnetic switch, and a coded transmitter, all in the valve stem assembly. Each sensor is registered to the car (so you don’t get somebody else’s warning as they drive next to you…), and the 2012 Forester handles 4 registrations. (None in my spare.) The receiver handles the warnings. Some cars will tell you which tire, but I haven’t heard of the Forester doing it. Since the sensor is switched, it doesn’t really activate until you hit about 20mph. I assume it’s a combination of an absolute set-point switch and a sudden decompression sensor. Haven’t needed the latter feature.
3) Ambient temps will have a serious impact on pressures. On the same gauge, I lost 2PSI from afternoon to the next morning, and regained about 1 with 2 miles of city driving two hours later…
4) The reregistration procedure uses a magnet to override the centrifugal switch and a laptop. I’ve seen third party software that would handle the task, might have been under Linux/GPL. If you switch to non-sensor tires, you get to seen the warning light turn on in about 10 miles. I went with non-sensor snow tires, so all winter I get to see the light.
5) Does your spare really have a TPMS? Mine doesn’t. If you look closely at the valve stem, you are supposed to be able to tell. Can’t remember the details.
6) I had a better dealer. [grin] The only thing they “forgot” was the full tank of gas they promised at delivery. OTOH, our area of Oregon is very serious Subaru territory. Between home and Chicago, I counted about 10 Subies on the road, but it’s a very popular car here. (We have 3 dealers with only 5 brands in the area, but the road conditions are ideal for a Subaru.) In 2012, east of the Cascades in Oregon may have been the only area where you’d find Subarus with Romney bumper stickers. [grin]
I can confirm, no Subaru has a system that tells the user what the pressures are actually at. They require you use a handheld guage for a proper reading. I can also confirm, that the spare tire does not have a sensor in it, and the TPMS system can only hold 4 tires at a time. Have two sets of tires on rims each with a sensor in it? The 8 sensors, (4 sensors per set) will continually have to be reregistered to the system each time you swap tires. Some customers bought two sets of wheels to avoid the $60 fee to swap tires each winter, but now still have to pay the $50 programming fee to register the sensors each time they swap. Frustrating for sure. I hope this sheds some light.
That makes buying the aftermarket TPMS reader and OBD-II programmer look downright attractive, even at $300-ish the set. I’d get winter tires on steel rims, so the payback would be about three years.
It seems Subaru also makes updating the TPMS memory as difficult as possible. Other manufacturers let you trigger the onboard computer, activate each sensor with a magnet, and you’re done. [drat!]
Careful re-reading of the manual says that it does not. Even if the doughnut spare has a sensor, it’d never get turned on, so what’s the point? I suppose having the TPMS light stay on serves to remind you that the spare needs changing now, although a friend with an Outback reports that installing the spare lit up all the drivetrain warning lights.
There’s a fair number here, too, perhaps because engineers (even ex-IBM engineers; a lot of that’s going on these days) tend to read Consumer Reports.
I’ve had these installed in the Prius and the Sienna:
A total of 4 sets (summer + winter each). They seem to be rock solid, and it is amazing to see how how much the tire temperature will be over ambient.
The main thing is I was after is an audible beeper if the pressure is too low. Save one flat from ruining the tire and it pays fore these.
Sounds like all your cars use the same rotation sensors as our Sienna. Once upon a time, I parked the van with one wheel in the sun and, sure enough, the TPMS indicator lit up half a mile down the road: that tire was 10 psi higher than the other three!
I have winter tires for the Sienna, but I’m hoping the combination of AWD, cowardly driving, and staying indoors when it snows will pull us through the next few winters…
Hey, I was reading your post about the sony vs wasabi batteries and I stumbled upon this post (The battery article is great btw thank you). I actually work at a Subaru dealer and we set the tire pressure to 37psi regularly. This is based upon the fact that 90% of our customers never check their tire pressure between service (3-5 months) and that you can lose 1psi per month from your tires and still be considered normal. The tire pressure light comes on at 32 or below. Putting them at 37 and very commonly finding them at 33/34 when they come back is better for the tires than starting at 32 and running way too soft at 26/27 chronicaly. I tell people, if you check your pressure regularly, 34 is a great number, but even 10 deg drop in temp can cause an effective 1psi drop registered by the sensors. We used to set the tires at 34 and had a TON of people calling in about the “mysterious horseshoe error light” or their “check engine light” is on shortly after service. Most people that bring their car in here for service don’t know how to check their tire pressure, are afraid of checking and adding pressure or simpley cannot do it. We have a lot of senior citizen clients and I am happy to help them. It saves everyone a lot of headache to just put them a bit higher and have that buffer between hot and cold weather causing false positives and natural seepage from the tires causing people to come in well before they are due for service again. I dunno, maybe thats still not “the right thing” to do, but I think it serves our customers well. Even with the higher pressure, we still see people wearing out the edges of their tires slightly before the center tread, but its much better than it was when we had people driving around on 26psi all the time. I hope thats an insight as to why the pressure may be set to that amount! Its perfectly safe, and only makes the tires a bit firmer… it doesnt detract from the safety. On my end, I am happy to not field TPMS light calls all day as well
Yeah, just walk through a parking lot and you can see that in action! [grin]
That can’t be true, as the B-pillar placard says 29/30. Maybe 22? (Although I agree that’s scary low; the potholes around here would eat those rims for lunch.)
On behalf of my long-departed mother, I thank you. If it weren’t for folks like you, the wheels would have fallen right off her old Taurus; she was not mechanically inclined!
That’s why I tend to run ’em a little tight, too: the recommended pressures seems tuned for maximum cushiness, rather than maximum tire life. The Sienna placard calls for 32 psi, with a max of 36 at max load, and I run them around 36 (in Hankook tires that max at 44 psi). Tightened up the ride and evened out the wear just fine.
Amen… but finding that “horseshoe light” in the manual requires serious deep diving!
Good on ya!
I sense a somewhat delayed honeymoon period with Fuji Heavy Industries. Perhaps after the next snowstorm you’ll develop into a full, Vermont-class Subaru zealot. I’m actually disappointed that they don’t implement the firmware to allow the dashboard to display actual tire pressures: Honda/Acura does this and has for years. Honda/Acura TPMS also seems to be substitution/replacement friendly – no complex, dealer-proprietary registration needed.
I suppose I don’t have nearly enough ego wrapped up in the thing; we needed a box with wheels and CU says this one should be less likely than the others to need repairs. Other than that, it’s just a small SUV that gets reasonable gas mileage.
Which, unless there’s a very pressing reason, we’ll enjoy from inside the house…
We got the Forester for cost/safety. Before we got it, our only winter option was a Silverado that loooves gasoline. [wince]. Getting into the garage quite literally requires 4WD/AWD, studded snows and a running start, so we needed something good for our own property and the chronically iced up roads around here.
With the Subie, we can do a round trip to town (80 miles, plus running around) and get 29 mpg in summer, and maybe 27 in winter. (16/15 on the Silverado…) In the forest we go through, we’re thrilled when the roads are clear, but it’s not something we count on. The Forester does the job. It’s rough if the road has thick slush, and high crosswinds make for an interesting drive. It wasn’t much fun during a high wind warning–55 mph gusts raise hell with the high sail area, though I was passed by a SMART car in that stretch. [hmmm]
FWIW, I bought winter tires/steel wheels from Tire Rack. These are studded, but without TPMS. Both are legal (Oregon DOT hates the studs, but they are widely used east of the Cascades), but I have to do the tire swap. A lot easier than for the Silverado. Even the service writer at the Subaru dealership doesn’t bother with TPMS, and the golden horseshoe is just another sign of winter. [grin]
Oh yeah, if you get steel wheels for those tires, get hubcaps, or a functional equivalent. The axle nut is exposed in the steel tire (capped by a plastic piece in the OEM wheels), and if you are in a salted area, you could have trouble. We’re in a part of the state where they use cinders and assume drivers have a sense of survival, so I tried duct tape the first winter, and skipped covers this one. No problems, but YMMV.
A combined solution seems in order: duct tape over the exposed axle nuts and the TPMS warning light.
Thanks for the tips…