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Where is the TCM and how do I replace it?

61K views 18 replies 7 participants last post by  rimwall 
#1 ·
if I was just going to replace my TCM because of error code P0725, where is it?

how big of a deal is it to try and pull off and check the connections and put back?

where do I get a new one?

I've seen the errors again a month ago, and now in the heat, I'm getting pretty hot on longer uphills, and just waiting for the main symptom of the engine dying on a slowing down, where it should be down shifting.
 
#6 ·
The indication MT/AT (manual transmission/automatic transmission) suggests it's not the TCM which is for the automatic only. The part number (88281AG10A) corresponds to the Body Integrated Unit.

Looking at some diagrams in the FSM, the BUI is to the right of the steering column; the TCM is to the left of the column, possibly further forward, closer to the firewall.
 
#8 ·
Not sure how you can test it except to swap it into another vehicle with the same TCU and test it in that vehicle.

Are you having a particular problem that a forum member may be able to assist with?

Seagrass
 
#10 ·
I am not sure whether you may have mistyped the year model or maybe the mileage.

Have you checked the transmission fluid level. A low transmission oil level will cause the symptoms you are describing.

If it is a 2003 Outback with only 29,000 miles do you know if the transmission fluid has ever been changed? Like most automotive fluids, transmission fluid can degrade with age and if it has never been changed it is now around 19 years old!

Before trying to find a replacement TCU or spending any amount of time diagnosing what the problem might be it may be wise to change the transmission fluid first as this is a quick, easy and cost effective thing to do and often shows very good results. Of course this may not be the cause of your problem.

If you are going to change the transmission fluid make sure you use the correct fluid for your vehicle and just do a drain and fill (about 4 quarts required). I would not worry about removing the transmission pan or changing the transmission filter at this stage as you are just trying to determine if new fluid resolves the problems or whether there are more serious problems with the transmission.

If you do want to look further into what is happening in your transmission you may be able to access the TCU using a windows laptop computer a Vag-COM OBD2 to USB cable and the FreeSSM software. This setup emulates The SSM (Subaru Select Monitor) equipment used by Subaru dealers for diagnosing problems.

Hope this helps,

Seagrass
 
#14 ·
Sounds like the transmission is “flaring” during gear changes.

Did you use the correct fluid for your model transmission? Incorrect fluid can cause flaring.

Did you check the transmission fluid level with the vehicle on a flat surface and engine running with transmission in Park? A low transmission fluid level will cause flaring.

If the above is all correct it is time for a professional diagnostic at a transmission workshop or experienced Subaru workshop (NOT a dealer).

There is no need to change the transmission oil filter as this will not be the cause of flaring.

Seagrass
 
#15 · (Edited)
Fluid level is Ok and I used Valvoline Dex/Merc ATF transmission oil which is recommended for Dexron III which my car uses. I took my car to AutoZone to have them check the "check engine" light code and it was the same that my reader gave me...P0731. AutoZone suggested the part that needs to be replaced is a Vehicle/Transmission Speed Sensor, Duralast Part# SU14028, $401.99. What are your thoughts on this? (The automatic transmission speed (ATS) sensor measures the rotational speed of the transmission shafts. Input and output transmission speeds are monitored and relayed to the ECM/TCM by either an analog or digital signal for proper shift points, speedometer operation and transmission diagnostics. Causes for replacement include check engine lamp illumination, poor or erratic shifting, no or erratic speedometer operation and the transmission going into limp/fail-safe mode. NTK automatic transmission speed sensors are made from high strength thermoplastic that is resistant to temperature, moisture and chemicals. Pre-installed O-rings precisely match OE material and diameter for ease of installation and sealing. The sensor output signal matches OE specifications.) Thanks.
 
#17 ·
Seagrass,
Well, I made some progress today. I did this sequence: "Engine control system • Let the engine run at idle until it fully warms up (the radiator fan turns 2 times or more) under no electrical load condition. • After the battery ground terminal is connected, wait for 10 seconds or more to turn the ignition switch to ON." Before I did this, I was in "Limp Mode" where I couldn't get out of 2nd gear and not over 30-mph or higher than 2,750 rpm. After I completed, I can now get up to 60-mph and maybe 3,400 rpm. Almost normal driving except for erratic acceleration and my check engine light still comes on. She's going into the shop tomorrow for diagnostics.
 
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