Tacoma with P0770 code

Well, you’ve started the process, but you have a way to go. When your Tacoma threw the 0770 code it was complaining that there was a problem with another solenoid, the Lockup Converter Solenoid. Normally, the Torque Converter Lockup Clutch maintains a 1-to-1 ratio between the input shaft and the torque converter so there is an effective lock between the transmission and engine. This is similar to the lock you achieve in a manual when you shift into a new gear and let the clutch back out. In reality, the lockup torque converter allows for a slight decrease in engine rpm so that can achieve better mileage while maintaining a speed. It is what is known as the “lockup torque converter” and functions like an overdrive setting.

Because you are seeing the P0770 code, the Powertrain Control Module (powertrain converter) is seeing a difference in the rotational speeds of the torque converter and the input shaft. The P0770 code appears when the difference between the settings is 200 rpm.

There are several possible causes of this problem. First, the torque converter lockup solenoid may be bad. Second, it may be a bad engine coolant temperature sensor. Third, it could be a bad torque converter clutch. Fourth, it could be a defective valve body or the tranny fluid may be dirty and the dirt is restricting its flow.

As to the specific cause of your problem, I would have you check the lockup solenoid. They should do more than just cycle the solenoid. Instead, your technician should monitor the solenoid in action during either a dyno test where the tranny goes through the gears or during a road test with you at the wheel. If that is working, then you will have to have them look at the engine coolant temperature sensor. Finally, I would urge you to have the converter clutch checked as well.

I honestly suspect the problem could be in one of the areas I mentioned. Indeed, I think you should swap out all three, if you can afford it. Make no mistake about it, this isn’t a $150 repair. Given the amount of teardown — the primary reason you do all three fixes at once — your technician will have to do, you are looking at a $1,750 to $2,150 bill. If you swap out all three parts while the transmission is open you will be taking care of the problem, whether it’s only one of the parts mentioned or all three.