Mercedes-Benz 722.8 TCU | Speed Sensor Faults

Common Issues and Solutions

If you're experiencing issues with your Mercedes-Benz transmission, particularly with the Mercedes-Benz Temic VGS (722.8) CVT / FCVT TCU, faulty speed sensors may be the culprit. Below, we highlight the common fault codes you should look out for and the steps to resolve the problem.

Common Fault Codes Related to Speed Sensor Issues

When your transmission control unit (TCU) encounters faults, it often generates specific diagnostic trouble codes (DTC) related to speed sensors. Here are the most frequently seen codes:

• P0720 – Speed Gradient nPrimGrd > nPrimGrdMax

• P0722 – No RPM signal from CVT output RPM sensor (component Y3/9b5)

• P0793 – Intermediate Shaft Speed Sensor Circuit No Signal

• P0794 – Intermediate Input Shaft Speed Sensor Signal Error

These codes typically indicate speed sensor faults within your Mercedes-Benz TCU.

Vehicles at Risk for TCU Speed Sensor Faults

These speed sensor issues commonly affect the following models:

• Mercedes-Benz A-Class W169 (2004 – 2012)

• Mercedes-Benz B-Class W245 (2005 – 2011)

If your vehicle is in this range and you're seeing related error codes, a faulty TCU or speed sensor failure could be the cause.

Causes of TCU Speed Sensor Faults

The primary cause of these issues stems from the Mercedes-Benz 722.8 transmission system, where the TCU relies on speed sensors (Y3/9B4 and Y3/9B5) that are controlled by the main circuit board. If the sensors are faulty or damaged, replacing them on their own may not solve the problem. In many cases, the issue lies deeper within the circuit board of the transmission control unit, requiring specialized repair techniques.

What to Do if You Encounter P0720, P0722, P0793, or P0794 Fault Codes

If you're dealing with P0720, P0722, P0793, or P0794 fault codes, the best solution is to opt for TCU remanufacturing. This approach is cost-effective and quicker than ordering brand-new parts. Remanufacturing addresses deeper issues within the TCU, including problems buried within the printed circuit board (PCB). Simply replacing sensors may not resolve these underlying problems.

The Vehicle Check offers a plug and play solution for remanufactured TCUs, and all our products come with a two-year warranty for your peace of mind.

Need Help with Your TCU or Speed Sensor Issue?

If you're experiencing speed sensor faults or need assistance with your Mercedes-Benz TCU, don’t hesitate to reach out to The Vehicle Check. We’re here to help with expert TCU repairs, remanufacturing services, and advice.

Contact us today at 0203 489 2610 to speak with one of our specialists and get your transmission control unit fixed quickly and reliably.