Automatic transmissions are often seen as the most intricate components in automotive engineering. While designing a reliable automatic gearbox is already a complex task, achieving it can be particularly challenging. Many manufacturers, including Volvo, rely on specialists like Aisin for their transmission systems. Unfortunately, this collaboration also leads to unique issues, such as the notorious Volvo S60 transmission problem.

The Aisin Episode

Aisin Seiki is a respected name in the automatic transmission industry, trusted for its long history and reliable products. This company has been a key player for over 71 years, contributing to the evolution of automatic gearboxes and dispelling the myth that they are inherently less reliable than manual systems. However, even the best can encounter pitfalls.

Aisin AF33 Gearbox

The majority of Aisin's gearboxes are designed for a range of vehicle makes and models, with few being exclusive to a single brand. The AF33 gearbox project is a prime example of this approach. In the early 2000s, Volvo collaborated with Aisin to create a new generation of automatic gearboxes intended for future vehicle platforms. This collaboration resulted in the AW55-50/51SN gearbox, which, at first, met all expectations. Unfortunately, issues soon emerged, with reports of gearbox failures occurring in vehicles with less than 50,000 miles. As warranty claims surged, it became evident that the AW55-50/51SN had inherent flaws.

The Volvo S60 Transmission Problem – Slush Box Strikes Again!

The S60 model was particularly impacted by these transmission issues, although the AW55-50/51SN gearbox affected several Volvo models. A comprehensive list of these models includes:

• 2000–2004 Volvo C70
• 2006–2013 Volvo C70
• 2000–2013 Volvo S40
• 2000–2007 Volvo S60
• 2000–2006 Volvo S80
• 2000–2004 Volvo V40
• 2004–2013 Volvo V50
• 2000–2007 Volvo S/V70
• 2000-2002 Volvo V70XC
• 2003-2005 Volvo XC70
• 2003-2006 Volvo XC90

Symptoms of transmission issues with the AW55-50/51SN are often clear-cut. Drivers have reported rough or erratic shifting, loss of gears (particularly the 4th gear and reverse), and fluid leaks. When these issues arise, they are hard to overlook.

It took Volvo approximately four years to acknowledge the problem and develop a solution, known as the B4 Servo Update.

B4 Servo Update and Other Solutions

The delay in providing a comprehensive fix stemmed from the sporadic nature of the initial gearbox issues, which were sometimes resolved through simple fluid flushes. Other shops attempted to solve the problems with software reflashes, which yielded mixed results. Ultimately, these were temporary fixes.

After extensive trial and error, Volvo developed a mechanical solution—the B4 Transmission Servo Update. This update kit includes several O-rings and a redesigned valve cover for one of the primary servos responsible for controlling hydraulic pressure and ensuring smooth shifts.

The original component sent by Aisin was under-engineered, leading to significant issues. Fortunately, the B4 update proved effective for many gearbox problems.

How to Fix the S60 Transmission? – The DIY Approach

For those inclined to tackle repairs themselves, the B4 update can be performed at home. Access to the servo cover is straightforward through the driver-side wheel well, held in place by two O-rings and a snap ring. The update kit comes with all necessary parts, but you will need fresh Genuine Volvo transmission oil for a complete oil flush, which should be done every 50,000 miles as part of regular maintenance.

After flushing the oil, it’s important to reflash the Transmission Control Unit (TCU) with the latest software. If you are not comfortable with this step, seek professional assistance.

The Not So Lucky Ones

While the B4 update has resolved many issues, it may be too late for some transmissions. If problems persist after the update, oil flush, and TCU reflash, a new transmission valve body or even a complete gearbox replacement may be necessary. Those who were able to address their gearbox issues under warranty were fortunate, as the AW55-50/51SN can fail unexpectedly.

If you're considering purchasing a used S60, be aware that many of these vehicles are priced low due to transmission issues. Ensure that the gearbox has been serviced with the B4 update before making a purchase. The cost of a new gearbox can exceed the vehicle's value, making the B4 update kit a wise investment.

Transmission Issues Prevention?

Preventing servo cover failure is challenging, but regular maintenance is key. Flush the transmission fluid every 30,000 to 50,000 miles to help prolong the life of the gearbox. Be vigilant with symptom detection; if you notice your gearbox hesitating or struggling to shift, consult a mechanic immediately. Early detection can prevent further damage to the valve body.

As you move away from 2004 models, the likelihood of encountering servo cover issues decreases. Volvo has made significant improvements in later models, reducing the risk of hard shifts. Still, checking the service history of any used vehicle on the list is essential—look for prior transmission issues and maintenance records.

Where to Find the B4 Update Kit?

The B4 update kits remain available almost two decades after the initial issues surfaced. As a leading supplier of Genuine Volvo parts, we have the kits in stock. If you're uncertain about compatibility or need assistance, our customer support team is ready to help. Reach out via our contact form for more information.

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