Why an Aveo automatic gets poor city MPG

[herbolero]

instead of shifting into fourth gear at 20mph, i can stay in 3rd gear, i like it better

yeah, im stuck with an auto, i would have a small turbo in here in a heartbeat if it was a manual though

Your car does not shift into 4th gear at 20 MPH. The shift points occur (approximately) as follows: second at 15, third at 25, fourth at 35, followed by torque converter lockup at about 45 MPH, which feels like a shift but it's actually the torque converter locking up.

So at 20 MPH you are actually still in second and are locking in second gear. You might have more acceleration, but it won't help your fuel economy.

Hmm.. i see now, but what would be the direct effect of starting to roll with the hold button on? From my understanding, and from how i felt when i used it, it's supposed to give me more power by staying on the current gear. But when i tried the hold button while at 50Kmh (~30Mph) it actually down shifted. Since then i never used it in fear of messing up the gears.

[petrified.rabbit]

i don't have an automatic, but are you sure it was a down shift and not the lock up turn off or on? or does anyone know if the hold button disables itself to prevent over revving / stalling?

[thehunterooo]

my hold button is like being in 3rd gear the entire time, i dont think you could over-rev or stall with the button on

if im going over 30 driving normally, it will down shift to the 3rd gear, at 50 or so you should be in 4th or th overdrive, so it will down shift

but i have never been able to get proof of what the hold button is or does, but thats what im assuming

[Thymeclock]

my hold button is like being in 3rd gear the entire time, i dont think you could over-rev or stall with the button on

if im going over 30 driving normally, it will down shift to the 3rd gear, at 50 or so you should be in 4th or th overdrive, so it will down shift

but i have never been able to get proof of what the hold button is or does, but thats what im assuming

As I understand it (and from what I've observed) the hold button only affects 1st and 2nd gears. The whole purpose of it is to be able to lock the A/T into either gear for things like driving on ice and snow, where you don't want it to slip into a higher gear when your wheels are spinning.

That's about all it was meant to do, and that's about all it is good for.

[thehunterooo]

ive read that too, but maybe its on the sceond gen aveos? I know ill shift from first to second the into D4 with hold on (3rd gear really) , then it shifts into 4th and then overdrive after i press the button again

starting out in third gear would help in snow, ice and rain, but thats how i use my hold button, like if i was downshifting on the highway to 3rd, i just press that button and im off :P

i did have a new front axle and such put in too, mabye something stange happened when i "wrecked" my car

[GADOLL]

I don't know about any of this stuff, but I'm very disappointed in my car. I know it's only 4 cyl. but I expected better gas milage than what I'm getting. Have only been out on the freeway a few times since
it's a new car and I'm told to break it in easy. So I vary my speed and watch my rpms.......but, with less than 500 miles on it it's getting horrible gas milage. My other car gets better around town and it's an 8 cly.
Maybe it will do better as it gets more miles on it, but right now I wish ..........

[Thymeclock]

I don't know about any of this stuff, but I'm very disappointed in my car. I know it's only 4 cyl. but I expected better gas milage than what I'm getting. Have only been out on the freeway a few times since
it's a new car and I'm told to break it in easy. So I vary my speed and watch my rpms.......but, with less than 500 miles on it it's getting horrible gas milage. My other car gets better around town and it's an 8 cly.
Maybe it will do better as it gets more miles on it, but right now I wish ..........

I'm assuming you have an automatic. Can you tell us the points (at what MPH) when each shift occurs?

[petrified.rabbit]

came across this (there is hope for you yet):

Yes - the transmission tune from the factory is terrible. In fact, by the time I bought my car, GM had already released an updated transmission tune (including a new operating system).

The Cruze uses a brand new transmission controller (called the T76) which is very similar to the T43 used in the existing 6sp automatics.

The Cruze does NOT come with a SPORT mode from the factory, but I added one to mine through the TCM tune. When the shifter is in D mode, it's one profile, and when I move it to the manual quadrant, it goes into an automatic-shifting "SPORT" mode, and then you can TAP it from there. When we get to select-a-tune working for the Cruze, I will probably tie it to this on the automatic cars.

The Cruze appears to have an LSD from the factory. When I floor it (with our tune on it), both tires spin. LOL.

The Cruze uses the same transmission as the 180HP Buick Regal 2.4L SIDI, so even with our cranked-up tune, we're well within the designed torque specifications.

As for tuning it goes, I've tightened up the shifts in SPORT mode, it made a BIG difference. The factory desired shift times are around .5 seconds. I pulled this down to .1 second and it shifts immediately. I need to work on downshifts yet, but initial results are very encouraging - better than what I was able to achieve with my Buick LaCrosse.

The 6sp automatics have a very sophisticated torque management system. It is possible to greatly exceed the design specs for torque input as long as you don't try to carry the torque through the shift. I've tuned 6sp automatic Corvettes making over 600HP at the input shaft of the transmission that live a long life yet because the TCM is so effective and getting the ECM to remove torque during shifts.

So, in short, with careful tuning, I believe the slushbox will be able to handle lots of power, and we might even be able to turn it into more of a gearbox. Haha!

since the cruze is essentially a daewoo just like the aveo, you might be able to get vince to tune the transmission for you to get better numbers.. mpg or otherwise.

[kkeenum]

i have a 2010 aveo5 hat auto 14,000 i need to know on the ATI which has 5 wires 2 top 3 bottom which one is hot and which one is ground any help is better than none 2 wires on topare black and brown on bottom are white brown and green

[alleycat_42]

Our 2009 Aveo5 is only a few months old with less than 2000 miles on it. We like the car very much except that the city MPG has been disappointing. The city EPA estimate is 25. The best we have been able to get is 22 MPG. After installing a scan gauge and driving very conservatively I was determined to find out specifically why the fuel economy is so inadequate.

After considerable research I found the transmission is made by Aisin, a Japanese manufacturer with a good reputation for quality transmissions. It is an ordinary 4 speed, with no overdrive. The same transmission is found on all Aveos made from 2004 to 2010. I recently found the service manual for this transaxle, Aisin 81-40LE. It can be found on-line at: http://www.anagabriela.ro/.../2. AISI ... NSAXLE.pdf

The graph on page 5A2-12 shows the manufacturer’s specification for shift points. (The graph is stated in KMH, so I’ve converted the figures to MPH for this discussion.) The graph shows the shift points will vary somewhat according to the TPS (throttle position) reading. On my car a scan gauge registers the TPS reading at idle at about 16; very conservative (slow) acceleration would be about 25; brisk or above average acceleration would be about 35 TPS.

According to the graph, at 25 TPS the shift points should be at about 11, 20 and 27 MPH. At 35 TPS it should shift at about 12, 22, and 32 MPH. I compared what I am actually getting on my car, at about 35 TPS, which would be considered average or brisk acceleration. I found it actually shifts at about 15, 25, and 45 MPH. In other words, the upshift into the highest gear (fourth) is much too late. Most 4 speed transmissions typically shift at approximately 10, 20 and 30 MPH. The delayed shift into high gear at around 45 is a major reason for delivering poor city FE. I live in suburbia. On major roads, typically the speed limit is 40. Unfortunately, when there is traffic it is impossible to break 45 – thus the car is spending most of its time in first, second and third gears at best, and it virtually never goes into high gear, which would yield the best fuel efficiency.

The transmission shift points are entirely determined by an electronic module called the transmission control module (TCM) which was designed and pre-programmed by Chevrolet. The shift points for which it is programmed are widely different than the documented specifications of the manufacturer, Aisin. I visited a Chevrolet dealer and spoke with the service manager to see if the TCM could be reprogrammed. He told me that they could do nothing to change it, unless Chevrolet had issued a service bulletin update for the program (which is has not done in the past five years that Chevy has been using this transmission on the Aveo). In other words, unless and until Chevy engineering rewrites the programming of the shift points and offers it as an update for dealers to install, nothing can be done to rectify the existing discrepancy. I then visited my local transmission shop (AAMCO) and asked the same questions. They confirmed that there is no way to reprogram the TCM unless Chevrolet rewrites the programming for it.

From what I have read on the web this is a very common complaint for Aveos. Most owners are unaware that their cars are late in shifting into fourth gear and frustrated with their poor city mileage. Seeing that there is documentation supporting the fact that the TCM programming of Chevrolet is greatly divergent from the specifications of Aisin, the manufacturer of the transmission, I believe Aveo owners have a valid grievance against GM and should press to have the situation rectified.

Who can we complain to? How can we unite to complain effectively and have Chevrolet correct this situation?

OK everyone here it is and I agree with everything you say about GM and their bad attitude towards Aveo owners and problematic vehicles.
While driving along at a regular pace and once the vehicle hits say 45 MPH or 2500 to 3000 RMP just quickly turn the ignition key on and off while driving and it will reset the TPS for some reason and shift into 4th gear or OD. I found this on my own and the GM dealer has no fix for the problem. This will save everyone a great deal of gas and also make your engine last longer because its RMP's are lowered. The next thing I might try on my own is to buy an EVEO Chip to see iof it will reprogram the shift points and I won't have to use my manual method of shifting into 4th gear. The Chip is only worth about $80. I will let everyone know if it works and good luck to all with the temporary fix. Please let me know if it also works for everyone out there.
Cheers Brian