The ECM or ECU is the electronic module at the heart of the Rav 4’s transmission system. In this instance, ECM stands for Electronic Control Module. You may also hear the item referred to as the Electronic Control Unit, which is shorthand for the same thing.
It is unhelpful, but true, that there is no such thing as a single ECM (or ECU) in a Rav 4. The two contractions are generic motor industry terms for the electronic modules or components specifically installed to perform a number of engine management functions. Therefore, if you were to call a garage and tell them you wanted a Rav 4 ECM repair, they’d ask you what unit you were referring to, and for a much more specific description of the problem.
Symptoms of Faulty ECM
The transmission ECM is known to fail on Rav 4 models released between the years 2000 and 2005. Symptoms of a faulty ECM include knocking when the gearbox is used; a clanking sound in reverse; jumping and bouncing; harsh gear changes; and loss of power through second, third or fourth gears. If left to fail, a replacement ECM can cost more than the value of the car itself. If left until the transmission is ruined, the cost of a fix can be even more.
The failing ECM is essentially losing control of the smoothness of the vehicle’s gear changes. This causes mechanical issues with the moving parts of the transmission – hence the sounds alluded to above.
It must be noted that failing gears and noises attributed to gears are not only symptoms of a faulty ECM. Before you diagnose the requirement for a Rav 4 ECM repair it may be necessary to eliminate other causes of poor gear change from the field. These include concomitant known issues with early model Rav 4s – for example, the known issue with early diesel versions whose flywheels cannot cope with heavy off road or dragging work.
In this instance, the flywheel begins to spin out of synch and the bolts loosen, causing slippery or juddery gear changes and loss of power. The fix is purely mechanical and may, if caught early, be less expensive than a new transmission – though a partial transmission rebuild is still quite a costly job.
Some five gear models in the catchment years alluded to above also have problems with rough gear changes, which are caused by a gear nut coming loose in fifth gear. Again, this problem is purely mechanical and may have nothing to do with the ECM.
The Toyota warranty applicable to gearbox issues in these early Rav 4 models has now expired, meaning that official Toyota dealers are no longer able to repair the vehicle without charge. It is possible that removal and repair of the ECM itself may correct the issue of harsh changes, though any actual mechanical damage caused by the harsh changing cannot be reversed without replacement of the affected parts.