Hard shifting issue & loss of acceleration 1999 Subaru Legacy 2.2L Automatic

1999 Subaru Legacy Wagon 2.2L Automatic
152K miles

Hoping someone has experienced this issue and may have some advice on the route of repair.

So far three mechanics (including the Subaru dealership) have been unable to resolve the issue or pinpoint the source of this issue. The issue is intermittent and random but very scary as it results in a total loss of acceleration and jolting hard shift. The tricky part is that it doesn't happen all the time and we can go up and down the interstate on long road trips with no issues at all.

In town driving is when the issue usually occurs. I have yet to have a mechanic be able to experience the issue when they road test - most likely because they do not have the time to drive it for long amounts of in town driving time.

This is an automatic transmission and the issue happens when you are in town driving at around 35-45 mph.

Conditions in which hard shift occurs:
Start and stop traffic i.e. between stoplights where you can get up to 35-45 mph. Also tends to happen when accelerating and then going down a hill or steep grade between 35-45 mph. For example accelerating up to a hill and letting off the acceleration (no brake just foot off accelerator) when going down the hill and then give it good amount of gas once it get to a slower rate of speed.

Most times this issue happens when going up a bit of a hill and giving the car gas or going down a hill while in gear but not giving the car gas and not braking (where the car has to regulate its own speed on a downhill grade).

When the issue happens you notice first a loss in acceleration and then the AT Oil light will start flashing and a very noticeable, jolting, and hard knocking shift where you won't be able to accelerate above 20 mph (like its stuck RPMs will rev with foot on accelerator but you cannot get above 20mph). The check engine light usually comes on AFTER the hard shift.

Sometimes however NEITHER the AT oil light nor Check Engine light comes on. The codes I have been able to pull when the AT Oil light has been flashing and the check engine light comes on are PO731 and PO122.

The only way we have found to get it "unstuck" from not being able to accelerate after hard shift is to let the car idle for 20 minutes or more OR turning the car off and on sometimes once but sometimes 2 or 3 times. This gets it back to normal and if AT oil light was flashing, this will go away and check engine remains.

On recommendation from our mechanic, we took it to a transmission shop to confirm that it was not transmission related or transmission computer related and they told us they could find no issue and suggested that it was something electrical not transmission related.

Since transmission was ruled out, we had our mechanic replace the throttle position sensor and that has not resolved the issue.

As a result and our our mechanics suggestion, we decided to take it to the Subaru dealership and the dealership mechanics said the voltage was set incorrectly on the Throttle Position Sensor (this voltage was actually set correctly by my mechanic and I suspect whatever is causing the issue is throwing the voltage out of whack).

The dealership mechanic readjusted the Throttle Position Sensor to spec voltage. The hard shifting accompanied by all the above mentioned symptoms happened again within a day after the voltage was set back to spec voltage by dealership. Took it back to dealership and they cleaned conductive grease of the Throttle Position Sensor's plug contacts - they said was put on there incorrectly by my previous mechanic and that would solve the issue. The hard shift came back after a day of in town driving so conductive grease was not the culprit.

Took it back to the dealership and left the car for an ENTIRE week at dealerships request! At the end of the week they still could not tell me what was wrong. The closest they could come to giving me an answer was that it may be electrical or that it is related to the engine wiring harness. Nothing conclusive though in terms of a diagnosis.

When I dropped it off to the dealership for the week, I set the trip counter to zero to see how much the car was road tested and it showed only 8 miles had been driven for road testing purposes for the whole week it was with the dealership mechanic.

The latest attempt to resolve the issue was in February 2013 where we had our mechanic who replaced the throttle position sensor have his diagnostics person run a series of tests. The diagnostics found two bad/ dirty grounds and that the throttle position sensor waveform had lots of electrical "noise" in the pattern. They cleaned all 7 engine and PCM ground points and road tested car and had no issues.

After all of this work was completed we had no issues for almost an entire month and thought the issue was resolved. Then the exact same issue returned! Feels like we are back to square one again and is a consistent annoyance.

The other symptom we have noticed which appears to be related to this issue is while driving on the highway above usually when driving between 60 and 70 mph and higher (2500-3000 RPMs), when letting foot off of accelerator to coast down to a lower rate of speed, when you put your foot back on the gas, rather than a smooth acceleration it jerks into a higher rate of speed and not a smooth acceleration of speed. You can see the RPMs jump rather than gradually go up. This makes it very hard to maintain a constant rate of speed. Then when you pull off the highway, the hard shift as described above happens.


At this point I am not sure what the next step if our mechanic or the Subaru dealership cannot solve? How on earth can I get an expert to pinpoint the issue without throwing money at possible problems?

Any suggestions are greatly appreciated - The only other place I have found a discussion related to this issue is here: http://www.justanswer.com/car/697fz-...#ixzz252mSRPn0

Thanks for your help!

i had a sort of similar situation.
random auto trans down shifts (rmps jumping up for no reason)
AT Temp light flashes, but there are no ''trans codes''
i never got a CEl but it was a bitch to drive.

what i found was a loose ground wire bolt on the intake near the coil. (passenger side)
this was on a 00 lego L ej25 engine.
the wierd trans activity was un explained and no shop had any suggestions, not the dealer.
i found one post on ultimatesubaru.org (96 outback) with a similar issue and it was blamed on a loose ground wire by the dealer. i did not believe it. but when i found the lose bolt , what the hell, i tightened it up and it fixed it.

check your ground wires. get an copy of the FSM to be sure you check them all.
i guess you can stop checking if you find a loose one.

until now, i have always discounted ground wires as causing problems, but not any more.

good luck.

Thanks for this info Johnegg - yes ground wires definitley sound suspect. I am convinced this is where the problem is occurring though my mechanic said they tested all engine grounds after they ran diagnostic. They didn't say they found any loose so a really good place to start. I actually spoke with an independent Subaru mechanic who said this year and model is notorious for this issue. Also pointed to the possibility of the engine wire harness being the culprit as well and that it might need replacing.

Forgive my ignorance but what is the FSM? Is it like the Hayne's manual but from the manufacturer? Thanks again for the help!

FSM = Field Service Manual, usually produced by the car manufacturer for the dealer mechanics to use.

there is usually a part of the wiring diagram that shows all the ground wire points under the hood.

there are several links for downloadable manuals. i don't have any but someone should. maybe a search would find some.

Thanks for clarifying FSM - I actually found one with very little difficulty doing a search. Will post an update once I find out more on the hard shifting problem.

So here is the latest in regards to the issues I have previously described:

Our most recent Subaru mechanic in April 2013 found the following:

1. One of my cooling fans was failing, bad wire so it wasn't even running.

2. Positive battery terminal wire completely shot so bad connection there which was replaced.

3. Mechanic adjusted Throttle Position Sensor above the recommended spec voltage (says from experience he does this because the car responds better to that setting).

Thought our problems were solved but then Hard shifting, loss of acceleration and same old symptoms returned after almost 300 miles of driving!

Took back to this same mechanic and decided to have knock sensor replaced.

Now a NEW symptom has manifested itself:

Now when putting gas on the accelerator, there is an uneven shift from 1st to 2nd gear and car seems to be struggling to get acceleration between gears. Very sluggish and even. This is most noticeable going from second to third. It feels like it isn't getting gas, accelerating very slowly up to around 25000 RPMs where it for lack of a better word BURSTS into third gear. The RPMs move very gradually and then ZIP up to 30000 RPMs. This issue is more frustrating than the hard shift issue as it happens ALL the time now during in- town driving.

AND the hard shift, loss of acceleration issue has again returned (the original issue) has returned. Pulling P0122 and P0731 codes same as before.

At this point I am not sure what the next step if our mechanic or the Subaru dealership cannot solve? How on earth can I get an expert to pinpoint the issue without throwing money at possible problems?

Any suggestions are greatly appreciated - The only other place I have found a discussion related to this issue is here: http://www.justanswer.com/car/697fz-...#ixzz252mSRPn0

If it's isolated to the transmission/powertrain, maybe check the powertrain control module. That controls the entire operation of the transmission and engine and if anything goes out of whack, it can cause all sorts of issues.

I experience a similar issue, but it's only when it's cold...when accelerating from 1-2, the rpm's shoot to 3000 before it bangs into gear. The shift is very firm. Not sure what's causing it, but it's only when it's cold so probably something in the transmission needs to warm up. It started doing it after a trip to the coast and got worse after a transmission fluid change. I'd reckon something's worn out.

Originally Posted by sirstinky

If it's isolated to the transmission/powertrain, maybe check the powertrain control module. That controls the entire operation of the transmission and engine and if anything goes out of whack, it can cause all sorts of issues.

I experience a similar issue, but it's only when it's cold...when accelerating from 1-2, the rpm's shoot to 3000 before it bangs into gear. The shift is very firm. Not sure what's causing it, but it's only when it's cold so probably something in the transmission needs to warm up. It started doing it after a trip to the coast and got worse after a transmission fluid change. I'd reckon something's worn out.

The Power Train Control Module (PCM) is this the same as the Electronic Control Module (ECM)?

Is this something I can check myself? I read in my Hayne's manual that I can tap vigorously on the computer box while the car is running and if the car stumbles or stalls, that can be a good indicator that something is wrong with the PCM. I do not have a SCAN tool to read engine data though I can at least try this and make sure all the wires are connected properly to the PCM too.

Also, what if I found that the PCM does need replacing? I have found them on Ebay but do I need to get them reprogrammed or flashed before putting the new PCM in the car if that is in fact the problem?

Thanks for any and all help!

Tap "vigorously" on the PCM? That's a new one!

Ok so the codes you're pulling are both powertrain related. The P0122 is related to the TPS, specifically a low voltage condition at the TPS, so your mechanic was correct in his assessment and in replacing the TPS. So I'm not sure why it's still signaling the DTC for it. Maybe it's a problem elsewhere in that electrical system? Maybe a bad connector somewhere. If the TPS is new and PROPERLY installed, and the voltage is good and doesn't jump all over, then it could be the 731 code throwing off the TPS code.

The other code, the p0731 is a transmission DTC. 731 is a code for an incorrect ratio on 1st gear, so apparently there is an issue somewhere in the transmission or the computer that controls it, i.e the shift points. By the way, the TPS does play a role (a pretty significant one) in how your transmission shifts, as the gears it grabs are dependent on throttle position. A problem anywhere in that system can make it malfunction and work improperly.

If your mechanic(s) have checked it out and don't find a problem with the transmission itself, then you might want to look into the PCM. Have a shop test it (they probably do more thorough tests than banging on it). That's all I can think of. It could be a bad wire somewhere, a frayed lead, break, or short. Did they test/check the wiring? If you have checked everything else with no solution then that could be the issue. I would look there before considering buying a PCM.

What would happen if a previous owner swapped out an tranny with the original thinking it would work but the new tranny had a different output ratio than the first? Could this cause problems, just a thought....

Could this cause problems

yes, of curse, but not the kind you are experiencing.
you would have torque bind.