Problems With The Toyota A343F Transmission and The Possible Culprits

Posted by on Wednesday, April 3rd, 2013

The A343F is a four speed automatic transmission built by Aisin-Warner for Toyota. It was produced between 1993 and 2002 and used in such vehicles as the legendary Land Cruiser and the Lexus LX 450 (both were four wheel-drives). Toyota has a reputation for building great vehicles and transmissions. This transmission is pretty reliable but it does still have its share of issues. If your shop works on the Toyota A343F transmission, or you have one in your vehicle you might want to take note of these common problems.

The Toyota A343F transmission


Symptom: Lock up converter is not functioning properly. Problem: There are a few things going wrong that could be causing this problem. 1) Check the stop light switch circuit. The lock up converter is designed to disengage when the brakes are applied to stop from burning up the converter clutch. 2) Check the engine coolant temp sensor and circuit. The system is designed in such a way that the lockup clutch will not function until the engine temperature has reached a per-determined level. 3) Check the ECM (Engine Control Module – a fancy word for the vehicle’s computer) using a hand held scanner. If no code is returned try unhooking the battery for 5 minutes. This will clear the computer and allow the transmission to “learn” all over again.

diagram of the different clutch packs found in the A343F


Symptom:  No movement in any gear including both forward and reverse. Problem:  Again, this problem can be the result of a number of different failures. 1) Check the shift solenoid using an ohm meter. The resistance inside the solenoid should read between 20–30 ohms. If you get anything outside that reading I suggest you consider replacing the solenoid. 2) Check the control cable. It could be broken or just unhooked. 3) Check the manual valve in the transmission. The linkage going to the valve could be broken or the valve itself could be broken or stuck. 4) Check the operation of the O/D direct clutch (refer to the shop manual for instructions). If the clutch pack is burnt up it will prevent the vehicle from moving. 5) Check the O/D planetary gear unit. Make sure the gear housing, bushings, pins and gears are all in good condition. Excessively worn or broken parts inside the assembly may be the culprit.

View of the palentary gears


Symptom: No movement in Drive, 2nd and Low. Problem: There is only really one thing that could cause this problem. Most likely the forward clutch pack has failed. Please refer to the shop manual on how to test the forward clutch pack.

The above mentioned problems are but only a few of the problems you might experience with the A343F. There will come a time in the transmission’s life that it will need to be replaced. My suggestion is to replace it with a re-manufactured transmission, not one that has simply been rebuilt. Why you ask?

A re manufactured transmission uses parts that are re-machined to factory specs, or replaced, if that can’t be accomplished. It’s basically as good as a brand new transmission at a greatly reduced price. A rebuilt transmission usually only consists of replacing the seals, gaskets and friction material (that is done in a re-manufactured transmission, too). A re-manufactured transmission will include modifications and upgrades that are designed to make the transmission more reliable, while at the same time extending the life of the transmission. A rebuilt transmission will usually not include these additional items. A re-manufactured transmission also usually comes with a much better warranty –  three years compared to an average 90 days for a rebuilt transmission.

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