2003 Subaru Forester Automatic Transmission mystery


I bought my 2003 Forester a year ago from a friend with 90,000. I love this car, I put a new timing belt on it and off we went. The car worked fantastically from January to August 2011. One night I was driving to watch a show and rather then shifting into gear, it jolted. Pulled over, checked fluids and so on, car worked normally for a while. It started doing this more frequently. It has a hard time shifting into 2nd and when it does, (at about 40MPH) it jolts and same thing for third and so on. I took it to my mechanic but it never misbehaved for him sop I took it back and drove some more and dropped it off at a transmission shops. They get it to do what it does, ran many tests, decided it was the throttle sensor, replaced it, car worked great for two weeks and then reverted back to this behavior. Took it in again three times but they can’t seem to figure it out. Anyway, I have taken the car to five different mechanics and no one can quite figure it out. So my car, the Diva, as I like to refer to her, continues to jolt to shift gears. If I put it into reverse it will shift normally until I stop again or slow way down. I am stumped and sad because I love my car. It now has 101,000 and I want it to be kind to me. Any ideas?

After 5 mechanics including a transmission shop, all of whom have actually been able to drive, inspect, & test things on the car, you’re going to have to pry some details out of them to report. Remote diagnosis by internet is a long shot to begin with.

What kind of transmission shop are we talking about? Is it a locally owned, independent place? Or a national chain shop? How did they determine that the TPS needed to be replaced? Was the wring for the TPS also inspected? When you took it back in did anyone put it on a scantool and determined that the TPS signal behaved normally? Someone should also inspect the mass airflow (MAF) sensor signal for abnormalities. Other than those questions, what have people done?

Presumably the car has been scanned for error codes. Were any found? If so report them as specific codes (format “P1234”).

Have the engine/transmission mounts been inspected?

The missing detail is whether the previous owner or the OP has ever bothered to change the transmission fluid and filter. While I would hope that the trans shop to which the car was taken did do a trans fluid change, it is also possible that they did not. But, if the fluid was changed for the first time at 90k+ miles, that is–unfortunately–at least 60k miles too late.

At this point, the trans fluid (and filter) should have been changed 3 times.
Has that schedule been adhered to?
If not, then I am not optimistic about the long-term prospects for the transmission.

When trans fluid is not changed every 30k miles, trans failure can take place any time after ~90k miles, and is pretty much of a sure thing by ~120k miles.

So the consistent code is: p0731. The shop that changed the tos is clary’s transmission and that was one of the codes.
My mechanic, Jim’s Auto Clinic in Shoreline Washington found the same code. He did some investigating and says it seems to be an internal related electrical problem with transmission.
Carter Subaru inspection says technician found valve body issue. Recommends new transmission.

I probably will not be able to get you very far as I am not a transmission tech. There is a very good one who visits here on occasion & he would be able to ask better questions & give better advice.

In the meantime…you said P0731 was one of the codes. There were others? That code is for an incorrect gear ratio & would not send anyone to the TPS. (The incorrect gear ratio is basically that the speed things are turning inside of the transmission is out of whack with the speed things are turning on the outside - given what gear you are in).

Back to VDC’s question, do you know whether or not the transmission was ever serviced? In particular, did this transmission place happen to remove the transmission pan for inspection? Did they run a full set of diagnostics on the transmission to check things like line pressures and solenoid functions?

I ask because I believe, given only the P0731, that you’d either be having a shift solenoid problem (relatively minor) or an issue with internal clutches (that’s bad & the transmission comes out to be rebuilt). An inspection of the pan contents might go a long way to telling you about serious internal issues. And full diagnostics would include making sure that all of the solenoids are behaving as expected.

Can you fill in the picture on what the transmission shop told you? They just said “we don’t know”? Or they said “we don’t know but we’ll install a new transmission for…$XXXX?” Or what? A good transmission tech can figure this out - not all shops want to put the time in though. They see a high mileage transmission, shrug & advise just putting in a new one. So what did they do & say?

I just sort of ignored the note about the Subaru dealer tech’s recommendation. I never trust those kinds of folks. However, I would not be surprised if you end up needing a rebuilt transmission.

Hi Cigroller,

Thanks for all your feedback. When they changed the TPS it was giving that code. Later came the code I gave you above. My mechanic did check the transmission pan and all looks clear. No metal shavings. He said they checked all the sensors, on the wheels and other places. I owe a lot on the car and around here the transmission rebuilds are going for 4 grand. Not sure if it is worth it…I guess what is hard for me to swallow is that no one seems to know quite what is going on. Yesterday my car was fine all day. Transmission was smooth shifting. Today started out fine and then started shifting hard. Do you have any recommendations in the Seattle area for expert transmission shop? Needless to say, I don’t want to do a rebuild if that isn’t the problem and I can’t get someone to say this is the problem. They are all slightly stumped.