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Thymeclock · 04-09-2010, 11:49 PM

Here’s an update on my A/T & city fuel economy situation on my 2009 Aveo after taking it to a Chevy dealer. They replaced my accelerator pedal assembly. They said there was a code set in the memory of the computer indicating it was not within correct spec range. Since I got it back I test drove it and here’s what I found: It now up-shifts a bit sooner into fourth gear – before it wouldn’t up-shift until about 38 MPH, and now it shifts at about 32. The shift into fourth gear feels a bit firmer (less murky) with a more noticeable drop in RPM’s when it shifts. The TPS reading I’m now seeing on my ScanGauge is slightly lower at idle, at about 15-16 TPS instead of 16-17 seen previously. So there is a perceptible difference, and marginally a slight but noticeable improvement in the way it shifts.

A few days before they changed the pedal assembly I took it for a drive on a stretch of highway with no traffic of about 10 miles. I maintained a steady 65 MPH with the A/C on the whole time (it was unseasonably warm here), and the Scan Gauge said I got 37 MPG for that highway portion! Apparently an A/T Aveo gets excellent highway mileage once the TC is in lockup mode – but short of speeds below 45, great fuel economy can’t happen.

I strongly urge anyone with the same murky shifting symptom to take your car to a dealer if it is still under warranty. Your car may have the same problem as mine and the accelerator deficiency may be more widespread than just an isolated case.

It’s too soon to tell with certainty whether our overall MPG improves any. I don’t expect to see much improvement as I’m still feeling a pronounced shift with an RPM drop into TC lockup at about 45. In other words, this probably rectified a relatively minor problem, but not the more prevalent one of the way the shifts are programmed. Unfortunately GM programmed this transaxle to delay TC lockup and treat it like a shift into overdrive. The sad and annoying thing is that there is no overdrive gear on this transmission beyond the actual fourth gear. The programming that delays the converter lockup amounts to fudging an up-shift into lockup mode, treating it as a sort of quasi-overdrive: as such, it is too little, too late.

04-09-2010, 11:49 PM	#2 (permalink)
Thymeclock Banned Join Date: Dec 2009 Location: NY Posts: 865 Thanks: 29 Thanked 111 Times in 83 Posts	Here’s an update on my A/T & city fuel economy situation on my 2009 Aveo after taking it to a Chevy dealer. They replaced my accelerator pedal assembly. They said there was a code set in the memory of the computer indicating it was not within correct spec range. Since I got it back I test drove it and here’s what I found: It now up-shifts a bit sooner into fourth gear – before it wouldn’t up-shift until about 38 MPH, and now it shifts at about 32. The shift into fourth gear feels a bit firmer (less murky) with a more noticeable drop in RPM’s when it shifts. The TPS reading I’m now seeing on my ScanGauge is slightly lower at idle, at about 15-16 TPS instead of 16-17 seen previously. So there is a perceptible difference, and marginally a slight but noticeable improvement in the way it shifts. A few days before they changed the pedal assembly I took it for a drive on a stretch of highway with no traffic of about 10 miles. I maintained a steady 65 MPH with the A/C on the whole time (it was unseasonably warm here), and the Scan Gauge said I got 37 MPG for that highway portion! Apparently an A/T Aveo gets excellent highway mileage once the TC is in lockup mode – but short of speeds below 45, great fuel economy can’t happen. I strongly urge anyone with the same murky shifting symptom to take your car to a dealer if it is still under warranty. Your car may have the same problem as mine and the accelerator deficiency may be more widespread than just an isolated case. It’s too soon to tell with certainty whether our overall MPG improves any. I don’t expect to see much improvement as I’m still feeling a pronounced shift with an RPM drop into TC lockup at about 45. In other words, this probably rectified a relatively minor problem, but not the more prevalent one of the way the shifts are programmed. Unfortunately GM programmed this transaxle to delay TC lockup and treat it like a shift into overdrive. The sad and annoying thing is that there is no overdrive gear on this transmission beyond the actual fourth gear. The programming that delays the converter lockup amounts to fudging an up-shift into lockup mode, treating it as a sort of quasi-overdrive: as such, it is too little, too late.