Shifting issues

[kstigler]

Good day..

'06 Aveo. a few weeks back, my son was driving it and it started to shift oddly.

He gets it towed to the house, we start digging in. Plenty of A/T fluid, idles fine. When running, it shifts "late" like in the 3,500-4,000 RPM scale. And when it shifts from 2nd to 3rd, 3rd seems to "shudder" almost like it's not sure it wants to be in 3rd.

scanned the engine, had some throttle position sensor errors, figured it was time to change out the throttle body. Throttle body switched out.. Idles better, still does not shift right.

Took some time to look at vacuum hoses. Found a couple of questionable hoses, replaced them. Small hoses, nothing much. took it out for a test. Seems to like 3rd gear better, but still shifts late.

had the transmission scanned by a friend who has a shop and offered to scan it. no transmission codes.

any thoughts? MAP sensor? PVC valve? Anything?

TIA

Ken

[avguy]

There was a recent no spark issue with this vehicle that you didn't follow up on. Checking on what was done to fix that problem, and if it's possible that something you did previously could be causing this latest episode.

[kstigler]

There was a recent no spark issue with this vehicle that you didn't follow up on. Checking on what was done to fix that problem, and if it's possible that something you did previously could be causing this latest episode.

Hmm.. Thought I did reply to that.. it was a fuse of all things.. Thought I had checked them all, but I missed one. What was weird is I found it while doing a voltage check around various components based on the schematic.. found one point of no voltage.. followed that back to a fuse with an odd label.

Replaced the fuse, the car started and ran for a few weeks..

[avguy]

Which fuse did you replace, and which TB codes were read? Fuses don't normally blow unless there is some underlying reason, so I suggest checking everything you can related to all of the circuits which are protected by that fuse. One possibility that comes to mind is wiring rubbed, scraped, or chewed, and causing a high draw. And that in turn could be affecting one or more components that the ECM and TCM are processing data to and from. Everything depends on specific voltages, and it doesn't take very much to throw off those computers.

[kstigler]

So, turns out the shifting issue was the catalytic converter melting.

I checked vacuum lines and replaced the intake hose, took it for a drive, the car couldn't even get past 20 MPH no matter how far the accelerator was depressed..

Got back to the driveway to smoke under the hood, popped the hood and the CC was on fire.. literally.. I put it out with a fire extinguisher and then promptly ordered a replacement online.

Showed up a few days later, I replaced the CC and the car drives like a scared rabbit now. After that I replaced the valve cover gasket and had him on the road..

[avguy]

Thanks for following up with the resolution to your problem. Did you also replace the O2 sensors? I'd be wondering if one of them got hot enough previously to melt enough insulation, causing a short which blew the fuse that you had to replace.