I have a 2008 GX470 with 115k miles on it.

Last winter (9 months ago, 5*F outside), I started a 30 mile trip home. The check engine light came on and the transmission would not shift properly, particularly if under load (accelerating / uphill). As I would accelerate normally (from a stop), the transmission would stay in 1st gear to 3500 RPM or so and stay at those RPM if I kept the accelerator steady at that position. If I let off the gas, it would shift a gear and this process would repeat, and I could get it up to about 50mph before it would no longer shift to a higher gear and rather the RPM's would just climb with no additional power through the tranny. I had driven 30 miles that morning with no issues, so the climate/cold was evidently not a factor.

I purchased a BlueDriver code scanner and drove the short distance to work the following week as the slower speeds on side streets weren't so much an issue. By the end of the week the vehicle was driving normally again. The codes that came up were P1441, P2440, and P2441 (air system switching valves stuck open/closed). Since the vehicle started driving normally I cleared the codes and moved on.

Today, (9 months later, 55* outside) I have the same problem and same codes. I drove a few thousand miles this summer and towed a 24' boat with no problems, so it must not be a mechanical issue with the transmission. It would seem to be some sort of computer problem controlling the transmission telling it when to shift, but there are no codes to that order. Having those same codes as listed above, I read up on them a little and it appears they are basically just a smog function injecting air to the catalytic converter so I wouldn't think that would have anything to do with the transmission shifting.

Has anybody had this problem? What was the cause & what was the fix?

Thanks!

 

Those codes point to part of the emissions system and are common on old vehicles with secondary air injection. If you don't have emissions inspections in your part of the country you can install a bypass system. Lots of people use the Hewitt one.

If you have never changed the transmission fluid, and you're over 100k, don't do a flush. Start doing drain + fills every 30k miles. This will get about 25-30% of the old fluid out. Be sure to use the exact same amount of new fluid to replace it - the transmission is sensitive to fluid levels.

Chip H.

 

Also check the transmission cooling lines for leak. My one rusted out and leaked.

 

https://hewitt-tech.com/