Toyota Tundra: Transmission Diagnostic Guide
The automatic transmission in the Toyota Tundra is generally very reliable; however, some problems may arise. Thankfully, they are well documented and most are easy to solve!
This article applies to the Toyota Tundra (2000-Present).
The Toyota Tundra has gained a great reputation of being a reliable truck; however, all trucks can face transmission problems after years of use and abuse. Some common issues that you might face are transmission fluid leaks, lack of response, refusing to shift, and whining from your transmission. The solutions to these issues can be very simple or complicated and expensive. The only way to find out is to diagnose the problem further and get to the bottom of the issue!
Materials Required
- Transmission fluid
- Flashlight
- Jack and stands
Step 1 – Check your transmission fluid level
A low transmission fluid level can lead to catastrophic failure, so make sure your fluid level is right.
The transmission fluid is essential to making sure your transmission is working correctly. It functions as a lubricant, cleans and conditions the seals, as well as acts as a hydraulic fluid inside your transmission fluid. All of these functions are dependent on your transmission fluid being clean and being filled to the right level. First, inspect for transmission fluid leaks by looking for reddish fluid on truck's undercarriage. Transmission fluid is generally not consumed like motor oil, so fluid levels do not drop over time, unless there is a leak. If there is a leak, then find the source and fix it. If you cannot fix the leak immediately, then add some fluid to make sure your transmission is not running low. If you are replacing your fluid, make sure to replace the filter as well.
Figure 1. Transmission fluid level. 
Figure 2. Transmission fluid leak.
Pro Tip
Do not overfill your transmission fluid, as this can cause many more issues than a low fluid level.
If your transmission fluid is clean, the level is good and you see no leaks, then proceed to the next step.
Step 2 – Check to see if your transmission slips
Worn clutches and a bad torque converter can cause your transmission to slip!
If you notice that your RPM's are climbing but your car doesn't move forward or accelerate, then your transmission is slipping. There are many reasons why the transmission might slip, but the underlying cause is that the internal components aren't meshing together like they are supposed to. The slipping increases friction inside the transmission, therefore the transmission heats up and more damage can occur. Unfortunately, just driving for a short time with a slipping transmission can cause major problems for your transmission. If the fluid level is not the issue, then seek a professional for a rebuild.
Figure 3. Torque converter replacement. 
Figure 4. Transmission rebuild kit.
Step 3 – Check if transmission refuses to change gears
An automatic refusing to change gears can be caused by many issues, so read below to find out some common causes.
It is possible to become locked out of a certain gear, or have one gear fail in your transmission. The most common cause of this problem is a low fluid issue; however, internal parts as mentioned above can cause your transmission to refuse to changes or go into drive. This is inevitably and expensive repair. One more issue that could cause your transmission to not change gears is a failed shift linkage. Refer to Figure 5 to locate your shift linkage. Have someone shift gears with the gear selector and make sure that the shift linkage is working properly. After thousands of cycles, the shift linkage can get damaged or bent, which doesn't allow it to function anymore.
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