My fuel mileage went from 15 mpg to 9 mpg this winter and the trans doesn't shift into overdrive till 65 or 70 mph and it used to around 50 -55 mph. The eng light is on (code says it is the knock sensor) and the od light is flashing.

The 3.5 is a great engine and in the Concorde pretty efficient for sure over 20 MPG. The 3.5 HO is 1st generation and has a 10.4 to 1 comp ratio. 89 octane is required later engines after 1998 had the compression ration lowered to 9.9 to 1 and 87 might be acceptable. Scheduled spark-plug change is usually 60K miles. If plugs have not been changed than I would certainty start with them. Check tire pressure against the driver door recommended. I expect if all else is well that at 60 MPH just under 2000 RPM in over drive and smooth..

This engine was built in Chrysler's Trenton engine plant in MI and is considered one of the best power planets at the time.

Might need a good tranny flush my wife hauls us mail we tried a sable and tranny went in three months but with no center console there nice

Roger, that doesn't even make a whole lot of sense to me. If the overdrive is causing the transmission to slip, wouldn't it also cause the fuel mileage to go down? Are you sure the transmission is slipping? Or is the transmission simply shifting in and out of overdrive? If it is, is it shifting at the proper speeds? Driving at around 40 - 50 Mph will sometimes make the transmission go in and out of overdrive repeatedly. This can be perfectly normal.

Have you checked your transmission fluid level?

Is your overdrive off light flashing? If the transmission is actually slipping the OD OFF light should be blinking at you to let you know there is a transmission problem. Either that, or the Check Engine light will be coming on. In either of these cases, you need to scan your onboard computer network for possible fault codes.

Hi, the late shift, and late overdrive issue may not be trans. related, if you need to feather the accelerator to achieve your shifts, and you have a late sift, or loss of power, you may have a restricted fuel filter. The lack of fuel volume can result in what feels like a trans. issue, but in actuality, you are starving the engine for fuel. I would check this first, as it is an easy, cheap possibility. Good luck...Coop

The D inside of an O is for overdrive. It is an automatic overdrive transmission. There isn't an overdrive button on it. If you want to disable the overdrive you have to shift down a gear.

When you turn it off it doesn't go into overdrive. If you do a lot of highway driving then you will notice a drop in your fuel mileage. Overdrive usually kicks in at around 40-45 MPH. Turning it off is usually done if you are towing or something similar where it would shift in and out alot. Hope this helps.

sounds like a restriction in the exhaust possibly catalytic converter...........

Sounds like the filter in the trans is plugged up. Should flush trans every 45,000 miles and replace filter and fulid. Its easier to take it in to a shop and have it done they use high pressure flush which will clean out the whole thing for about $200.

The ETC switch is a transmission control device. When it is not active, the transmissions shifts normally. When the ETC is engaged, it alters the shift points.
Example: the 1-2 upshift occurs normally between 18-20 mph. Now, say you are towing something, or are carrying a heavy load...engage the ETC, and the trans computer will "hold" the 1-2 upshift until 22-24 mph. It is just for that, prolonging the shift points, due to load.

The switch on the side of the shifter is for the Overdrive. Engaged (the OD light is off) the transmission shifts into overdrive. This saves you gas. When the button is dis-engaged (the OD OFF light is on) , the transmission does NOT shift into overdrive. It is best to leave the overdrive ON, and the ECT OFF to obtain maximum fuel mileage. I hope this has answered your question. Please feel free to comment back if you have any other questions. Thanks for chosing FixYa for assistance.

Your speed sensor in your trans. needs to be checked out sounds like its not working or not getting a good signal until its generating enough power and speed to start until it reaches 30 MPH. Check that out sometimes it could just be some dirt on it. It all makes sense the ABS light is on because its not reading the speed of the tires, and the AOD light is on because It has no idea when to shift into overdrive without knowing how fast its going. I sure Hope that Helps You Out, And Thanks, Bear001