Working on A 6T40 Transmission? You Will Want To Read This!
Posted by Regis on Wednesday, June 5th, 2013
The 6T40 is a six speed automatic transmission made by General Motors. It is designed to be used in transversely mounted applications and is part of a family of transmissions that also includes the 6T45 and 6T30. This transmission was first put into production in 2008 and remains in production today. It was used in the Chevrolet Cruze, Malibu, Epica, Tosca, Aveo, Sonic and Equinox. It was also used in other GM brands Saturn, Buick and Holden. In addition, it was used in select Daewoo vehicles. The 6T40 transmission is used mainly behind smaller four cylinder engines and is considered a lightweight design. The fact that it was used in so many different brands of automobiles means that it is likely that one will eventually show up in your shop for repairs. Let’s take a look at a couple of common problems associated with this transmission.
Symptom: The transmission starts to shift erratically. Possible cause: One of the issues include taking higher rpms, many times over 3000 rpms, to shift between gears 1st and 2nd gear, and 2nd and 3rd gear. Another one involves hard, jerky shifts. The factory recommends that you re-program the computer up to three times in a row to get the problem to stop. Then they recommend having you let the customer drive it for a couple of weeks to see if the problems go away.
You might also want to change the transmission fluid. There are reports of this helping to cure the symptoms.
Symptom: Shifting problems between gears. Possible cause: This transmission is very advanced and full of electronics. This includes electrical solenoids that are designed to electronically shift the transmission. The solenoids contain a coil of wire that when energized, creates a magnetic field. This magnetic field then moves a plunger that is attached to a valve in the valve body. When the solenoids fails, it can usually be traced back to the coil of wire that makes up the electrical magnet. The wire has a tendency to either completely break or internally short out. Many times, this is caused by excessive heat in the transmission.
To check the operational condition of a given solenoid, all you need is a hand held ohm meter. Connect the lead from your ohm meter to the two wires coming off the solenoid. A properly working solenoid will usually return a reading somewhere between 20 – 30 ohms. A reading outside this range might indicate a problem with the solenoid. If a solenoid is found to be defective, they are easily replaced and fairly inexpensive.
If you find your customer’s vehicle is past the factory warranty period and not easily or economically fixed, you should strongly consider replacing it with a re-manufactured transmission over one that was simply rebuilt.