This is going to be lengthy but it tells all I've done to troubleshoot.

We live in San Diego, CA. My wife’s car, a 2004 Hyundai Accent with 177,000 miles, has developed a transmission issue. Temperatures at night are in the 40s, day temps are 70s to 80s.

A couple weeks ago she had some problems, engine revving but transmission not kicking into gear immediately even though in DRIVE. I guessed and our mechanic Jeff confirmed it was a transmission problem. The transmission fluid had never been changed to my knowledge (we bought it used) so Jeff changed the fluid.When he dropped the pan we found shredded metal, several about ½ in. long kind of like ribbon. There were also several chunks of metal about 1/8 in. dia. He went ahead and changed the filter and cleaned out all of the metal in the pan. He put it back together and filled it with fluid. I drove off and the transmission performed great, just as it should.

The next morning around 5:30 I took it for a test drive. I noticed it would shift up normally ending up in 3rd gear. Going 50 mph it wouldn’t shift into Overdrive. I slowed down but it wouldn’t downshift but stayed in 3rd. I took it back home.About 8:30 that same morning I took the car into town. The transmission worked beautifully, shifting as normal even into OD. It worked great the rest of the day. No noise, no smell.The next morning about 8:00 I took it out again. The same thing happened, it shifted into 3rd gear and stayed. After about 6 or 7 miles I pulled over and put the car into P and shut the engine off for about 10 sec., restarted and took off and the transmission worked great. I drove at speeds up to 70 mph (legally), it shifted like it should, downshifting up hills and going into OD.I stopped and talked with Jeff (our mechanic) telling him what I found. He was baffled. He thought that maybe the gears heated up enough to compensate for the missing chunks, just a speculation.

So the next day I started out with the same problem, staying in 3rd gear. I went about a ½ mile, pulled over and leaving the engine running I moved the shifter to P, then to L, then to 2nd, then to P, then to D and started driving again. The car stayed in 3rd gear. I went about another ¼ to ½ mile, stopped, put the car into P and shut it off for about 10 sec. Started up and took off and the transmission worked GREAT!!!I took it back to Jeff and he ran diagnostics on it with no error code showing up for anything. I asked him if it could be in the computer since when I shut the car off it reset something so the car runs fine. He said he didn’t think so since there were no error codes on diagnostics.

The next day I started out with the same problem, stuck in 3rd gear. I only went ¼ mile or so stopped put it into P, shut it off for about 5 sec. Started back up and drove off with everything running GREAT.

A few days later I went out in the morning and started the car, I didn’t shift the transmission at all. I forgot something in the house so I shut the engine off, ran in the house, taking only 2 minutes or so, started the car and drove off. The transmission worked great!So now we start it up, let it run for a minute or so, turn off for about 30 sec., start back up and go and the transmission works great.

My question is: Could it be a computer/sensor problem that is not registering because something resets after I shut the engine off without shifting the transmission?

 

MIL,, start out in wrong gear ?? Scan it...


Drives fine with start out in 1, shift to 2, shift to 3, and thats it ?? ---> Check at the base of the shifter for the small OD switch harness having a broken wire... 3 wire in a sheath.