Overdrive switch

I have owned my 2002 Toyota Corolla Verso 1.8 auto for almost seven years and it has a threespeed + overdrive autobox. It sometimes hesitates in changing into overdrive from third gear. If I switch the overdrive button on the gearstick to ‘Off’ and then immediately back ‘On’ again, the ’box changes up into overdrive without any hesitation.

Is there a sensor that controls this action? I have had the gearbox oil changed by the main dealer, but they cannot find any fault with the ’box – but given that it is intermittent, this doesn’t surprise me. I am aware that the autobox will not change up into overdrive until the car has warmed up, as stated in the owners manual.

I would appreciate your thoughts on this. Geoffrey Allen

The overdrive control is regulated by the transmission control unit. When the overdrive switch on the gearlever is in the ‘On’ position, the contacts are open; when it’s in the ‘Off’ position, the contacts should be closed. I would check the operation of the switch using a test lamp and also inspect the OD2 terminal on the TCU. If no external fault can be found, the problem is most likely the TCU itself and the action of operating the switch when the overdrive conditions are met is triggering the action. When the switch is left in position, the TCU doesn’t trigger the operation once the conditions (speed, temperature, etc) are met.