Automatic gearboxes – Fault detecting

Posted on May 3rd, 2018 by GEM Motoring Assist

Automatic gearboxes - Fault detecting

While space precludes listing common failures for every automatic gearbox made in the last twenty years, the following five points are typical symptoms of a worn, or failing, automatic gearbox that are detectable while driving:


  • Slipping gears, to sudden rising engine revs between shifts (‘flare’) – This tends to be caused by low oil pressure, or incorrect (maybe even poor quality) fluid being used. Look for incorrect fluid levels, as well as a blocked oil filter.


  • No clutch lock-up from the torque converter – tends to be caused by an electrical problem and not the transmission. Check the brake pedal switch, as lock-up should cancel, when the pedal is depressed. As lock-up functions only at normal operating engine temperatures, a faulty coolant temperature sensor might be responsible.


  • Delayed engagement after selecting ‘Drive’ or ‘Reverse’ – look for a worn, or damaged, gear selector cable, or loose linkages. Dropping food, or drink, into the gear selector mechanism can affect the electrical contacts and all that may be needed is a degree of interior trim dismantling and a good clean.


  • Missing gears, or no drive – Most commonly, this is caused by faulty gear-speed sensors mounted on the transmission. It is possible, with some gearboxes, to mix the connectors around by accident. Have a live diagnostic check conducted to evaluate the readings, before suspecting that the more expensive gearbox internals are the cause of the problems.


  • Noise – any new sounds indicate a problem and should be investigated immediately, not only for safety but also to prevent catastrophic damage that results in expensive repairs.