Help diagnose shifting problems

[AndyE62]

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!

[RX400h]

Did you check the transmission fluid level? Was the fluid ever changed?

[JennB]

Any solutions to this issue?

[RX400h]

7 hours ago, JennB said:

Any solutions to this issue?

Quote

t sounds like you’ve encountered a frustrating issue with your 2008 Lexus GX470. Let’s dive into this and explore some possible causes and solutions:

1. Codes P1441, P2440, and P2441: Secondary Air Injection System:

   • These codes relate to the secondary air injection system, which is part of the vehicle’s emissions control system.
   • The secondary air injection system introduces fresh air into the exhaust stream to help reduce emissions during cold starts.
   • The valves associated with this system may be stuck open or closed, causing the check engine light to illuminate.
   • While these codes are related to emissions, they might not directly impact transmission shifting.

2. Transmission Shifting Issue:

   • Given your symptoms (staying in 1st gear, difficulty shifting, and high RPMs), it’s essential to address the transmission issue.
   • The fact that the problem resolved temporarily and then recurred suggests an intermittent issue.
   • Here are some steps to consider:

3. Check Transmission Fluid:

   • Ensure that your transmission fluid level is correct. Low fluid levels can lead to shifting problems.
   • If you haven’t already, check the transmission fluid level and condition. If it’s low or discolored, consider a fluid change.

4. Transmission Fluid Change:

   • Regular transmission fluid changes are crucial for maintaining proper function.
   • If you haven’t changed the fluid recently, consider doing so. Use the recommended fluid type for your GX470.
   • A fluid change might help if there’s any contamination or wear affecting the transmission.

5. Transmission Control Module (TCM):

   • The TCM controls transmission shifting based on various inputs (speed, throttle position, etc.).
   • Intermittent TCM issues could cause erratic shifting behavior.
   • Consider having the TCM checked for any fault codes or issues.

6. Valve Body Inspection:

   • The valve body inside the transmission contains solenoids that control gear changes.
   • A malfunctioning solenoid or valve could cause shifting problems.
   • An experienced mechanic can inspect the valve body and perform necessary repairs.

7. Electrical Connections and Wiring:

   • Inspect all electrical connections related to the transmission, including sensors and solenoids.
   • Loose connections or damaged wiring can lead to communication errors between the TCM and transmission components.

8. Professional Diagnosis:

   • Given the complexity of modern transmissions, I recommend having a professional technician diagnose the issue.
   • They can use specialized diagnostic tools to pinpoint the exact cause.
   • Share the history of your symptoms and the codes you’ve encountered.

Remember that addressing transmission issues promptly can prevent further damage and potentially save you from costly repairs down the road. If you’re not comfortable diagnosing the problem yourself, seek professional assistance.