The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0720.
DTC/P0720·Mercedes-Benz
P0720 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
High SeverityNot safe to driveMercedes-Benz
P0720 on a Mercedes-Benz means the transmission control module is not receiving a proper signal from the output speed sensor. This sensor measures how fast the transmission output shaft rotates, which determines vehicle speed and helps the TCM calculate gear ratios and shift points.
Typical repair cost, all makes€85 - €350
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Mercedes C-Class (722.9)
2007-2024On the W204 and early W205 C-Class with the 722.9 (7G-Tronic) transmission, the output speed sensor (Y3/8n3) sits on the conductor plate inside the gearbox together with the control unit, so it is not an external sensor you can unbolt. P0720 on these models usually means a conductor plate repair or replacement.
What causes P0720 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0720 page, these are the patterns noted for Mercedes-Benz models:
Mercedes C-Class (722.9)722.9 conductor plate integrated sensor failure
Mercedes C-Class (722.9)Conductor plate electrical connector degradation
How to diagnose P0720 on a Mercedes-Benz with OBD2
Follow these steps to pinpoint the root cause of P0720:
- Check if the speedometer is working. A dead speedometer alongside P0720 strongly points to the output speed sensor, since both the transmission and instrument cluster rely on this signal.
- Locate the output speed sensor on the transmission housing (typically near the tail shaft or differential housing). Inspect the connector for corrosion, loose pins, or damage.
- Measure sensor resistance with a multimeter and compare to manufacturer specifications (typically 300-1200 ohms for a magnetic sensor). With the car safely raised and the gearbox in neutral, turn a drive wheel by hand and check that the sensor produces a signal.
- Compare input and output speed readings. Vehicle speed is standard OBD2 live data, but transmission input and output speeds usually need manufacturer-level software. The output speed should correlate with vehicle speed and the current gear ratio.
- If the sensor and wiring test normal, inspect the transmission fluid for metal contamination. Debris on the magnetic sensor tip can cause signal distortion.
How much does P0720 cost to fix on a Mercedes-Benz? (EUR)
Estimated repair costs for P0720 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Codes related to P0720
These codes are often seen alongside P0720 or point to related issues, on any make:
Looking for the full P0720 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0720 guideSkanyx · Mercedes-Benz
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