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2002 Subaru Forester L 2.5 H4 Engine

Hello friends. Today, I’m looking at my girlfriend’s 2002 Subaru Forester. This little beauty has 192K miles on her. And the main problem I’m facing with her is the automatic transmission. Overall the car seems to handle well, however when going around 30-35 MPH and it shifts between 2nd and 3rd gear, it’s rather clunky. This seems to be consistent. If she manually rows through 1, 2, 3 and D she said she had no problems. I know extremely little about transmissions in general.

I’m thinking it would not be the Torque converter. I feel like if it were the Torque Converter, this problem would be consistent through all gears since the converter acts like an automatic clutcjh. (please correct me if I’m wrong there).

I would also hope it’s not the internal gearing of the transmission since I would think it would still clunk through the manual shifting.

I did check the transmission fluid and it is a pretty bright red. I do find this to potentially be problematic as the person who sold it to me told me that the transmission was flushed approximately 20k miles before hand. This was done along side a partial engine rebuild (gotta lover those old boxer heads).

Not really sure where to go from here. I suppose an obvious first step would be to scan the computer for Transmission codes. There’s no transmission lights on on the dash but never hurts. (Yes I have a BlueDriver Bluetooth scanner that I hope can check all codes on the subaru).

I will throw what I found in terms of Check Engine light codes as well, however I’m doubting it’s related.

    a. Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor)
    i. Solution: Replace Knock Sensor
  2. P0483
    a. Cooling Fan Rationality Check Malfunction
    i. Solution: Unknown as of now.
  3. P0447
    a. Evaporative Emission Control System Vent Control Circuit Open
    i. Solution: Unknown as of now.
  4. P0420
    a. Catalyst System Efficiency Below Threshold (Bank 1)
    i. Solution: Potentially fixing the exhaust leak may fix this.

One thing I always consider is whether the correct fluid has been used in the trans. It’s not always knowable, unfortunately.


not so fast!

I used to have 2003 Outback, and that generation was famous for “piston slap”, where Subaru made pistons too short, resulting in piston slapping against the cylinder, which is very easy to hear when car is started in cold weather, then it disappears as it warms up

I do not recall which particular code it was throwing, but for me it consistently returned back, even after replacing sensor

on this one, you might get lucky fixing leaks and/or replacing sensors (at 198K miles they are overdue for replacement), but if not - convertor itself is due for change

Thank you. At this point I’m more concerned about the transmission getting resolved. Although the knock sensor code does concern me slightly now that you’ve mentioned that. It does have a sound i thought was a bit strange but it seemed like comparing it to what other people said it was ( typical subaru boxer sounds) Using this video as a reference, if this is what piston slap sounds like then I’m about positive I don’t have it.

no, it’s not THAT bad, more like this:

verbally, it can be described as a sound one would get beating with a stick on the glass’ edge, ti is not loud and is fainting quite fast as pistons warm up, but it was enough for me to get the error code connected to the knock sensor

on transmission, you better replace the fluid 2-3 times driving few tens of miles in between

Walmart’s SuperTech Multi-Vehicle Auto Transmission fluid is cheap, they also carry similar one from Valvoline, it’s even better, both have Subaru ATF compatibility listed on the back label

you might consider replacing transmission fluid filter before the final change too: it is installed externally, you do not need to drop a pan to do it

Subaru has had more than one design of automatic trans and it’s important to know which fluid they recommend for yours. The owners/service manuals should say. Replacing the trans fluid filter is also a very good idea.

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older generations were pretty much all compatible to “standard” Mercon/Dexron III to my recollection, I’m sure “multi vehicle ATF” is exactly what doctor prescribed, but YES, it’s the best to check the manual/specs,2002,forester,2.5l+h4,1378739,transmission-automatic,filter,8600

That sound still sounds a bit off from what I’m hearing but I wouldn’t rule it out…I’d probably have to take it to a mechanic to know for sure. I’ll probably clear codes and keep an eye on it to see if it returns. If the code returns, I’d say it’s reasonable to assume that there is some kind of knocking going on ( probably piston slap). In regards to the transmission. I’m just curious what is leading you to believe that the fluid in this case is the problem?

transmission uses valves to shift gears

valves control fluid flow

if you get dirt accumulated there, valves tend to “stick”, resulting in jerks or slow shifts

normally, you have to replace ATF every 30K miles per Subaru maintenance spec

since you question the need for ATF changes, I can imagine you do not know if it was ever changed, so I assume the scenario I described above is plausible

I’d definitely say it’s possible. Although assuming what the guy selling me the car told me is accurate, the whole system was flushed only 20K miles ago. That’s more or less why I questioned it.

the “multi-flush” I described above is to save the neglected transmission with an unknown ATF age, not replacing filter can lead to oil starvation and premature death

you do not know if ATF was changed before that “20K before” flush?

in this case, $2 filter and $18 jug of Valvoline multi-vehicle ATF from Walmart will be a cheap insurance

still, it’s almost 200K miles on this car, at some point transmission will go… :frowning:

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Agreed. Yeah I don’t expect this car to be in any perfect lol. It was an 800$ beater from someone nearby. If we can get a year out of it I’d be pretty happy. Anything that’s relatively inexpensive that can potentially extend it’s life span will be benefecial. Plus it helps me learn more and more about working on vehicles. Also Unless I looked at wrong information, I do have to remote the transmission pan cover to remove the filter. Granted it’s not hard to access, just a bunch of bolts holding the cover on. I just want to make sure we’re on the same page.

This could be the “accumulator” in the transmission sticking. This is a small piston inside the transmission whose purpose is to absorb shock in the line pressure circuit in the transmission during or just after a shift. It won’t hurt anything to leave it alone. When i rebuilt certain automatics years ago, upon reassembly the accumulator was frequently installed in the garbage. I would, however, treat this transmission to a pan drop and filter change, preferably at a Subaru dealer, where you have at least a good chance of it being filled with the correct fluid. And relax, it’s not the torque converter or planetary gears.

Being that the biggest reccomendation is to change the fluid and filter I believe I’m going to go with that route. The owner’s manual says that Dexron 2 or 3 may be used which I found plenty of dexron 3 at walmart for cheap. I think a gallon was like 12$ or so

OH I just noticed on Rockauto that there are two types of transmission filters. Ones that look like an ordinary Oil filter then one that you would drop the transmission pan to remove. I guess I’ll need to look to see which one I have. I thought I rememver looking underneath and seeing an additional “oil filter” and being slightly confused. that could simplify things greatly.

this is how it looks where filter is attached:

considering you have 8 inches of ground clearance, should be possible to look there without lifting it up

Yeah I can sneak under there fairly well. I’ll check it out tomorrow. I’ll keep everyone updated. Thanks everyone for their help so far.

At 17 years of age and near 200k miles it’s also possible that it’s time for a transmission rebuild. After all, every one of the seals and so in in that transmission are well aged and as all seals do they tend to harden and leak or weep with age.

Check the transmission fluid level first. If that’s ok, probably do a proper service, meaning on many cars to drop the trans pan, drain all the old fluid out, clean the inside of the pan, replace the filter, and refill w/fresh fluid. If that helps but doesn’t solve it 100%, drive a couple hundred miles and do it all again. New fluid will have fresh seal conditioners, and the seals must hold for the transmission fluid to build to the levels needed to shift properly.

Even better would be to take it to the best trans shop in your area (ask you regular mechanic who that is), and have them read the trans codes, test the various pressures , and offer up a pro-diagnosis. Could be just a solenoid needs replacing, who knows. It’s possible this actually is a torque converter lock-up problem too, given that it acts up in the 35 mph speed range. That’s a very common thing reported here, not just on Subies, but many makes.