Flashing O/D light and transmission shifting

2008 Accent, A/T. In cold weather the O/D light on the dashboard will flash about once per second as soon as the vehicle is started. Once the vehicle warms up, it stays off. Occasionally when driving the O/D light will quickly flash and the transmission will shift from 4th to 3rd and then back to 4th. I've confirmed that it's not the control wire or button on the shifter. The overdrive button works normally when the problem is not happening. Overdrive works fine, pushing the button takes it in and out of overdrive just fine. I've traced the wiring from the button all the way to the ECU and nothing appears to be damaged. Disconnected the O/D button for a while and the problem still happened. Checked the connectors on the ECU and the intermediate connectors in the under hood fuse box. No codes are being recorded, at least none that my small code reader can see. Anyone else that has seen this? I'm thinking the flashing O/D lamp is telling me that something in the transmission is not right but without a code it makes no sense. I'm thinking I may need a better code reader to capture the data. BTW, in very hot weather (it gets 100 degrees + here in the summer) the problem never occurs. Thanks for any leads and info.

 

i had the same problem on accent 2010 , if you solve this problem could you please share the way to solve it

 

Just to close the loop on this one. The problem was the ECM (Engine Control Module). I got to thinking about the hot/cold weather difference and figured I would just simulate hot weather by warming up the ECM with a heat gun. I did that one cold morning and voila! No problem.

The back story on fixing this is that I had to go through 3 junkyard ECMs before finding the right one. Everyone kept insisting that what they were sending me was correct. But the first two fixed the o/d light and shifting problem but would throw a P0501 code for incorrect vehicle speed sensor input. After going over the schematics and checking ViN numbers of the donor vehicles, I finally figured out that the first two ECMs I received were from vehicles that did not have ABS. My accent has ABS. So we searched all the online junkyards that provided VIN numbers with their ad for an ECM and finally found one that had ABS. There is a very nice tool online that will tell you everything you want to know about a vehicle just by the VIN number. Popped that one in and all was well. I also learned through this exercise that ABS was an unusual option. My Accent was a rental car originally so that likely explains why it has ABS.

The interesting thing about the donor vehicle is that by the VIN number it had exactly the same options that ours has and was made just a month later. With only 114K miles on it this ECM should be good for a long while. I think my problem was just a fluke. I'm an electronics guy so I'm going to open up the old ECM and poke around to see if I can see any obvious problem like a cold solder joint or something. Certainly an interesting problem.