07 Limited Transmission

[HiltonII]

I have an 07 Limited and live in New Orleans area. I was wondering if I need to shift out of overdrive when in a mountian area. Previous car was Grand Marquis and I would shift from overdrive to the normal drive position when in steep mountain areas. This would keep from the transmission shifting in and out of overdrive and add to the down hill braking. So what I'm asking is what position to drive in when in mountain driving?

[new echo owner]

It depends on how the vehicle is responding to the driving condition. If it is shifting in and out of gears a lot, by all means. If there isn't much change noticed, and the transmission/engine are both moving steadily alone and no noticeable performance concern, it probably won't make sense doing that.

N.E.O.

[HiltonII]

I understand that but what I'm asking is what is the position to put the shift in? On my Merc it had Drive with an O and regular D which was no overdrive. On this car I only see a Drive position.

[new echo owner]

If you really want to, you can manually pull it down to the lower gears, I think both top two gears are overdrives, can't remember for sure, but they just don't label them that way. Again, it depends on how the car is responding, just because you had to do that with you Merc, doesn't necessary mean that you have to do that with the Avalon. You are talking about two very different vehicles and two very different power train design. Since no one knows what kind of road condition you actually drive through, so it is difficult to make any suggestion on what position you should have your transmission in to operate; try pulling it down one gear and see how the car response.

N.E.O.

[inov8]

Your Avalon ECM/TCM (Engine Control / Transmission Control Module) should automatically downshift out of the overdrive gear(s) as appropriate when driving in the in mountains. You can elect to leave it in "D" and let the ECM make the decisions for you.

I copied the paragraphs below from the 2005 Avalon factory TCU manual. The '05 transmission has only 5 forward gear ratios, but the same principles should apply to your 07. You can verify this feature for yourself by comparing the RPM versus forward speed relationship in hilly areas versus when driving on relatively-flat terrain.


7. Shifting Control in Uphill/Downhill Traveling

General
This control minimizes the shifting of gears when the driver operates the accelerator pedal while driving on a winding road with ups and downs, in order to ensure a smooth drive.

Shift control in uphill traveling
When the ECM determines uphill travel, it prohibits the transaxle from shifting up into 5th after the
transaxle has shifted down bellow 4th. When the ECM determines uphill travel with a steeper grade, it prohibits from shifting up into 4th after the transaxle has shifted down bellow 3rd.

Shift control in downhill traveling
When the ECM determines downhill travel, it shifts down the transaxle from 5th to 4th in accordance with the brake operation signal that is input when the driver operates the brake pedal. When the ECM determines downhill travel with a steeper grade, and a brake operation signal is input again, the ECM shifts the transaxle down from 4th to 3rd.

Uphill/Downhill Judgment
The actual acceleration calculated from the speed sensor signal is compared with the reference acceleration stored in the ECM to judge uphill or downhill traveling.

[HiltonII]

Thanks, I'll see what happens. I was not aware of the ECM/TCM.

[Amaury]

The 5th and 6th gears are overdrive, and their corresponding ratio are 0.71:1 and 0.61:1 respectively. I agree with inov8: If you’re not in a hurry, let the computer decides which ratios are best suited for your current load conditions.

Amaury
'08 Limited