@dlm welcome to the forum from Oregon!

I'm not going to be much help to you, as there's no mention of the TPMS in my 2008 Subaru technical service documents. I suspect this feature was added late in the model year & added to the later documents?

I do have these links bookmarked:

(All Years) - Sackett's g-whiz posts - a.k.a...

Trying to restore my street cred so starting a new thread with things I see in the shop. Today's picture is the geared idler pulley in the timing belt. It is THE MOST FAILED PART in the timing belt system. I do not stress over subaru water pumps. The one on the right was the lucky one. It failed...

www.subaruforester.org

('06-'08) - 2008 - What is this plastic box...

I just purchased my first Subaru Forester last month with the plan of using it to haul the new pup around and to do some car camping in. The current plan is to build a platform across the back as low as possible for maximum height room. After removing the rear seats and stripping out all the...

www.subaruforester.org

Also...

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Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]

 

Not sure why your FOB stopped working if it was just the battery. It shouldn't need to be reprogrammed. The ones for my wife's old '08 never did in the 12 + years we owned it since new.

Do you have the other FOB you can try? I had one FOB fail and when I opened it I found one of the buttons had snapped off the circuit board under the rubber overlay.

As for the TPMS, if your light is on it usually indicates one or more of the sensor batteries in the tires (part of the valve stems) have failed if there is no other problem found ( e.g. low tire pressure).

When was the last time you had them replaced? They only last around 7 years or so on average. Hers lasted about 9-10 years IIRC. .....so did mine on my own car. One just went out two days ago in fact so now I have my two fronts that are dead. In her '08 there was just the light so the tire shop would have to determine the ones that are dead but if it's been a number of years, best to get them all replaced.

 

@Kean Yes, I tried the other fob. Didn't work either, which is why considered reprogramming...or this potential linkage to the TPMS module. (Updated my original post with that info...and the fact that it's been super hot, in case that helps)

 

@dlm Ok, that's more clear now and I understand the connection.

Yeah, never knew there was a relationship there.

 

@dlm here's a long shot... system reset. It most likely won't work, but it will only cost a bit of your time. On the link below, do steps [1] thru [4]. If you have idle issues, do it again, doing all the steps.

Bobby...

(All Years) - How to Idle Re-Learn after Battery Disconnect!

Posting here as this seems to affect some Forester and Imprezza models with Electronic Throttle Bodies or IACV that undergo a battery disconnect, and lose their idle calibration. As per these links to retrain the ECU idle parameters: https://forums.nasioc.com/forums/showthread.php?t=2382568...

www.subaruforester.org

['07 FSXT Member Journal] ['03 X Member Journal]

 

Fixed!

Turned out to be as simple as cleaning the contacts and boards on both fobs with q-tip + rubbing alcohol! What threw me off was my second fob didn't work the same time the first was failing...so I figured the problem was something more serious inside the car. So I cleaned the 2nd fob (worked), then cleaned first fob (worked). All good now.

 

@dlm the factory fobs come with a light coating of dielectric grease on the battery contacts. This coating can be lost when the battery is replaced. The contact springs can also get loose, over time.

For the dielectric grease to be effective, the contacts have to be cleaned first & the circuit board to battery contact needs to be tight. Then a very small amount of dielectric grease is applied.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]