722.6 Gearbox: 5G-Tronic Problems, Codes and Replacement

The 722.6 gearbox is Mercedes-Benz's 5-speed automatic, often called the "5G-Tronic", and the predecessor of the 7G-Tronic 722.9. The most frequently reported 5G-Tronic problems are a leaking connector, which lets transmission fluid travel along the wiring harness into the control unit, and faults in the conductor plate that carries the speed sensors. The typical result is limp mode, where the gearbox only drives in 2nd gear and reverse.

What is the 722.6 gearbox?

722.6 is the series designation of the Mercedes-Benz 5-speed automatic transmission. It is a conventional torque converter automatic: a hydrodynamic torque converter with a lock-up clutch transmits the power, and the gears are selected through planetary gear sets, clutches and brakes. It was fitted for many years across a wide range of models, including the C-, E- and S-Class, the CLK and the SLK. Other manufacturers such as Jeep and Chrysler used it too, where it is often known as the NAG1. Its successor is the 7-speed 722.9.

One key difference from the 7G-Tronic: on the 722.6 the electronic transmission control unit is not inside the gearbox but mounted elsewhere in the vehicle. It is linked to the electronics inside the gearbox by a wiring harness and a connector on the transmission case. Inside the gearbox sit the valve body with its solenoid valves and the conductor plate with the speed sensors. Most complaints start at exactly these points.

Where is the transmission number?

The transmission number starts with 722.6 followed by two more digits, for example 722.618 or 722.699. You will find it on the identification plate on the gearbox casing. Listings usually write it without the dot (722618). The last digits identify different versions, which must match the engine and torque rating, among other things. If the plate is unreadable, a Mercedes workshop or parts supplier can identify the fitted gearbox from the vehicle identification number (VIN). Our guide on how to find your engine code explains where engine and gearbox codes are located for each make.

5G-Tronic problems: typical symptoms and causes

Specialist workshops and repair reports mention the following complaints on the 722.6 time and again:

• Leaking connector: the electrical plug on the gearbox case is sealed by a connector sleeve (also called a pilot bushing) with O-rings. Once these start to leak, fluid escapes and can wick through the strands of the wiring harness all the way into the transmission control unit. The results are poor contacts, fault codes for solenoid valves or speed signals and, in the worst case, a damaged control unit.
• Conductor plate and speed sensors: the speed sensors are part of the conductor plate inside the gearbox. Metal particles in the fluid can collect on the sensors, which then send implausible readings.
• Limp mode: when the control unit detects a fault, it switches to limp mode. The car will then only drive in 2nd gear and reverse.
• Harsh shifts and a shuddering converter lock-up: rough gear changes or judder at steady speed are often linked to aged transmission fluid.

None of these symptoms points to a single cause. Always have the fault memory read first, check the fluid level and condition, and inspect the connector on the gearbox for traces of oil. Whether a repair makes sense or a replacement gearbox is the better option depends on the findings. One important point when swapping the gearbox: if fluid has already reached the wiring harness, the harness and control unit should be checked as well. Otherwise the fault may return even with a different gearbox.

Maintenance: fluid and filter as specified

The 722.6 has a fluid filter in the oil pan, so a transmission fluid service usually covers fluid, filter and pan gasket. Keep the following in mind:

• Only use automatic transmission fluid with the Mercedes approval specified for your vehicle.
• Follow the service schedule. Even though the fill is described as long-life, many specialists recommend changing it regularly, because fluid ages over time.
• The fluid level is checked at operating temperature (around 80 °C) with a dipstick, as the manufacturer specifies. Too much or too little fluid can cause shifting problems in its own right.
• Use the fluid service to check the connector for leaks at the same time.

722.6 or 722.9: differences and interchangeability

The 722.6 and the 7G-Tronic 722.9 are often confused, but they are different gearboxes:

The two are not interchangeable: you cannot simply fit a 722.9 in place of a 722.6, or the other way round. Read more about the successor in our guide to the 7G-Tronic 722.9.

Finding the right replacement gearbox

Within the series, too, one 722.6 is not the same as another. This is how you find the right version:

1. Read the full transmission number from the identification plate, or have it looked up from the VIN.
2. Search for that exact number, for example 722618, 722699 or 722640.
3. You will find all 5-speed automatics of this series in our 722.6 category, and more Mercedes transmissions under Mercedes-Benz gearboxes.
4. Check in the listing whether the torque converter is included. This is stated in the title or description.
5. Compare condition and mileage, and if in doubt, ask us with your VIN.

Used or remanufactured?

We offer 722.6 gearboxes in different conditions, and the condition is stated in every listing:

• Used: removed from a vehicle, checked before dispatch, mileage stated in the listing. 12-month warranty.
• Remanufactured: professionally dismantled, cleaned, wear parts replaced and then tested. 12-month warranty.
• New: new part with 0 km. 24-month warranty.

The warranty has no mileage limit. What the total cost depends on, such as condition, mileage, labour and additional parts, is explained in our guide used, remanufactured or new; the same applies to gearboxes as to engines. Gearboxes usually carry a core deposit of €250, which is added to your basket automatically. You get it back in full once your identical, complete old gearbox has arrived and been checked, most easily by handing it to the haulier on the same pallet. Delivery is by freight forwarder on a pallet, usually within 3–7 working days. Have the gearbox fitted by a professional workshop and the fluid checked to the manufacturer's specification; that way your warranty remains fully valid.

Need help choosing?

Not sure which 722.6 version fits your vehicle? Call us on +49 4950 93890 (Mon–Fri 8:30–12:30 and 13:30–17:30) or email info@motoren-dejong.de, ideally with your transmission number or VIN. Or browse our 722.6 gearbox category directly.