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Thymeclock · 03-11-2010, 08:04 PM

I think I now know why Aveos with automatic transmissions get such disappointing FE in city driving.

I recently found the service manual for the four speed Aisin 81-40LE. It can be found on-line at: http://www.anagabriela.ro/Manuale%20...0TRANSAXLE.pdf

The graph on page 5A2-12 shows the 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 reading. On my car the TPS reading at idle is about 16; very conservative (slow) acceleration would be about 25; normal or average acceleration would be about 32.

According to the graph, at 25 TPS the shift points should be at about 11, 20 and 27 MPH. At 32 TPS it should shift at about 12, 22, and 32 MPH. I compared what I am actually getting on my car, at about 32 TPS, which would be considered normal or moderate acceleration. I found it actually shifts at about 15, 25, and 45 MPH. In other words, the upshift into the highest gear (fourth) is too late. The delayed shifting into high gear at around 45 is a major reason for delivering poor city FE. My old Celica had a 5 speed automatic, and it would shift into fifth (overdrive) at about 38-40 MPH.

I live in suburbia. On local streets I am finding that it helps to accelerate to 15 MPH ASAP to get into second gear and then glide to the inevitable stop sign at every corner. 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.

Would anyone know what is involved in reprogramming the TCU?

03-11-2010, 08:04 PM	#1 (permalink)
Thymeclock Banned Join Date: Dec 2009 Location: NY Posts: 865 Thanks: 29 Thanked 111 Times in 83 Posts	Aveo automatic transaxles and fuel economy I think I now know why Aveos with automatic transmissions get such disappointing FE in city driving. I recently found the service manual for the four speed Aisin 81-40LE. It can be found on-line at: http://www.anagabriela.ro/Manuale%20...0TRANSAXLE.pdf The graph on page 5A2-12 shows the 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 reading. On my car the TPS reading at idle is about 16; very conservative (slow) acceleration would be about 25; normal or average acceleration would be about 32. According to the graph, at 25 TPS the shift points should be at about 11, 20 and 27 MPH. At 32 TPS it should shift at about 12, 22, and 32 MPH. I compared what I am actually getting on my car, at about 32 TPS, which would be considered normal or moderate acceleration. I found it actually shifts at about 15, 25, and 45 MPH. In other words, the upshift into the highest gear (fourth) is too late. The delayed shifting into high gear at around 45 is a major reason for delivering poor city FE. My old Celica had a 5 speed automatic, and it would shift into fifth (overdrive) at about 38-40 MPH. I live in suburbia. On local streets I am finding that it helps to accelerate to 15 MPH ASAP to get into second gear and then glide to the inevitable stop sign at every corner. 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. Would anyone know what is involved in reprogramming the TCU?