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Discussion Starter #1
Hello all,

I purchased my first Subaru(03 legacy wagon 4EAT with 166000 miles, has about 180000 now) last February and I love the car. After searching through the forums here I figured I'd start my own thread and maybe get some pointers/advice from the experts here on an Issue I've been having lately. Sometimes while driving, the AT Oil Temp light begins flashing and doesn't stop until the car is turned off. This in turn makes the Check Engine light come on as well. Typically it only seems to happen when it is very hot or very cold outside. Yesterday was in the 30s all day and the AT Oil Temp began flashing on my way to work, and on my way home, today is in the 50s and it didn't do it this morning. Also, I think I've began to notice some correlation between the AT oil temp light flashing and the air controls inside the car. Is this possible?

The first time this happened was late summer/ early fall so I took my car to a friend and plugged up the OBD2 scanner. The code it gave was P0743 Torque Converter Clutch Solenoid Circuit Electrical. Since I hadn't really noticed any issues with the AT I decided to just clear it and see if it comes back up.... and it has. I know there are quite a few forums here with vehicles throwing the same code, however none seem to really be quite the same as mine.

The car runs and drives great, there is nothing I can notice about it's performance that would help pinpoint what particularly is going on. I've kept up with general engine maintenance and all fluid levels are good, AT fluid looks clean.

I think my first plan of attack this weekend is going to be testing AT wiring and hopefully that will help solve the problem without dropping the pan. If that doesn't work I think Ill have to drop pan and inspect wiring/ solenoids/ sensors there.
If that doesn't work I really don't know what to do. I don't particularly want to take it in somewhere, I enjoy doing stuff like this myself. However I think there may come a point when it goes beyond my capabilities and would be best to just take it to a mechanic.

With that being said, does anyone have any advice to give this novice? Pointers? Things to consider/ look out for? Really anything would help and be much appreciated.

Please let me know what ya'll think, and let me know if there is any info that I left out that would help. I look forward to hearing your responses


Premium Member
2001 VDC/SC One of a Kind
12,587 Posts
First, I'd check the battery and the cabling. A weak battery, one that is not providing ample ampere output, not necessarily voltage, will cause problems, especially with an automatic transmission. Since you also posted that the AC controls act up, it's probably related to a poor battery and bad ground cables.

You would have to have a meter that can measure ampere output with the battery cold and then check conductance through the cables, the negative from the battery to the lug by the starter and the positive from the battery to fuse box, battery to starter and alternator to the fuse box. On the main cables you don't want more than .2 ohms resistance. Then check the body grounds, once you get the main ground good, and you should not have more than .4 ohms resistance between the battery negative post and the ground lugs on the engine and body. There's a main ground lug on the intake manifold, 2 actually bolted down side by side, one by the ABS module, one by the fuse box, 2 on the firewall, one that runs from the top of the transmission by the pitch stop mount and connects to the the top bracket for the pitch stop on the firewall. Then you have a cable under the car that connects the heads to the frame rail, 2 on the lower radiator bracket for the lights, horn, etc.

Beyond that, the TCC applies at speeds over 28 mph and light throttle in 4th. It also engages when engine load levels and in 4th when cruising. Without TCC lockup the engine speed stays high and the torque converter continues to slip and increases the fluid temperature. So more fuel consumption and shorter fluid life. Once the code sets the TCM stops trying to engage the clutch until the next key cycle. This helps to keep the clutch from burning up. It may already be burned up and you may be looking at a new torque converter to fix it. But check the electricity supply and cables first.

There's also a ground wire on the valve body that can come loose and this can effect the TCC solenoid as well as the shift solenoids for the gear train and the center diff clutch. If/when you pull the pan, it's the black wire and just bolts to the bottom of the body.
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