Ask a Mechanic: The touchy reality of some transmissions

Dear Ask a Mechanic,

I bought my Toyota RAV4 new, and it now has 180,000 kilometres on it. A couple of years ago, I took it to the dealer to have the transmission flushed as part of its regular servicing. Shortly afterward, the car started to jerk and hesitate when going into third gear.

The dealer recalibrated it and it worked great for three weeks but the issue came back. I then took it to a transmission shop, where they dropped the transmission pan and found nothing abnormal. After, a second recalibration was done, and the vehicle worked perfectly again for five months.

Now, the issue is back, and a third recalibration has done nothing to fix the problem. If I accelerate slowly or quickly, it doesn’t hesitate to go into third gear. But it does hesitate if I am accelerating ‘normally.’ I have been told possible fixes include valve body replacement, third gear shift solenoid replacement or transmission control module replacement. Have you seen this issue before? – Troubled Transmission

I’ve seen something as simple as a multipurpose transmission fluid causing shifting problems in vehicles after they are serviced. I don’t believe the dealer you originally brough your RAV to would have used anything other than genuine Toyota approved fluid, I only mention it to illustrate just how sensitive modern transmissions can be.

Although most automotive service technicians (included me) will maintain and repair certain parts of an automatic transmission, diagnosing and rebuilding them is a specialty. I raised your question with transmission service technician Eric Vandepol, who has 30 years of experience in the field.

While the reader does not mention what year their vehicle is, Vandepol said early generation RAV4s, those from 2012 and earlier, are among the Toyota models known for engine control module faults. In these models, the module handles the transmission shift control and may, or may not, be able to recognize and flag a problem with the system. The reader does not mention whether any error codes have been reported.

Vandepol said the valve body would need to be removed to perform tests on it, but this will only prove if it is bad. It may also test fine while the vehicle is not running and cold but act up when it is in use. He said the same is true of the solenoids, but those should set off an error code if they fail.

Given the costs involved in fixing the issue, Vandepol said he is hesitant to say that the engine control module is definitely the issue without having inspected the vehicle himself.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to wheels@thestar.ca. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.