P0720 on Mercedes-Benz
Output Speed Sensor Circuit Malfunction
P0720 on Mercedes-Benz vehicles indicates output speed sensor circuit malfunction. Au7o has documented this code across 3 Mercedes-Benz models — most commonly on C-Class, E-Class, SLK-Class. P0720 indicates a malfunction in the transmission output speed sensor circuit. The output speed sensor measures how fast the transmission's output shaft is turning, which the computer uses to calculate vehicle speed, control shift timing, and manage torque converter lockup. When the signal is missing or implausible, the transmission may shift harshly, get stuck in one gear (limp mode), or the speedometer may read incorrectly. The fault is usually in the sensor, its wiring, or the connector, though internal transmission issues can also be responsible. Typical repair costs on Mercedes-Benz range from $500 to $3,000, depending on the specific model and root cause.
Common Causes of P0720
- •Failed output (vehicle) speed sensor
- •Damaged wiring, connector, or corrosion in the sensor circuit
- •Metal debris on the sensor tip or damaged reluctor ring
- •Open or short in the signal circuit
- •Low or contaminated transmission fluid affecting components
- •Poor ground or reference voltage to the sensor
- •Faulty transmission control module (TCM/PCM)
P0720 on Mercedes-Benz by Model
Mercedes-Benz C-Class(2 issues)
- 7G-Tronic Valve Body Failure2005-2013
The 722.9 7G-Tronic automatic transmission develops valve body issues causing harsh or delayed shifts, particularly the 2-3 and 4-5 upshifts. The conductor plate (electrical connector inside the valve body) is also failure-prone.
- 722.6 5G-Tronic conductor plate failure (limp mode, stuck in 2nd gear)1996-2002
The 722.6 five-speed automatic (fitted to W202 facelift cars from ~1996 onward and all 2001-2002 W203s) uses an electronic conductor plate mounted on top of the valve body that integrates the speed sensors and routes signals to the solenoids. The plate fails for two reasons: (1) the internal RPM sensors get coated by ferrous wear particles when the fluid is never changed, producing implausible-slip codes, and (2) the soldered traces and embedded capacitor crack from heat cycling. Failure puts the transmission into limp-home mode — stuck in 2nd gear, harsh 1-2 and 2-3 shifts, or no upshift at all. Often accompanied by codes P0717, P0720, P0731-P0736 and a transmission warning light. This is the single most common 722.6 failure across every Mercedes chassis that uses it.
Mercedes-Benz E-Class(1 issue)
- 7G-Tronic Conductor Plate Failure2003-2012
The 722.9 7G-Tronic transmission conductor plate (internal electrical board with speed sensors) fails, causing limp mode, harsh shifting, and loss of gears. The electrical connector corrodes or the sensors crack from heat cycling.
Mercedes-Benz SLK-Class(1 issue)
- 7G-Tronic Conductor Plate / Speed Sensor Failure2005-2011
The 722.9 7G-Tronic automatic transmission used in later R171 models is known for conductor plate and internal speed sensor failures. When the plate or sensors fail, the transmission may enter limp mode, shift harshly, or get stuck in one gear due to loss of accurate input/output speed data.
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View P0720 across all makes →Frequently Asked Questions
What does P0720 mean on Mercedes-Benz?▼
P0720 stands for "Output Speed Sensor Circuit Malfunction." P0720 indicates a malfunction in the transmission output speed sensor circuit. The output speed sensor measures how fast the transmission's output shaft is turning, which the computer uses to calculate vehicle speed, control shift timing, and manage torque converter lockup. When the signal is missing or implausible, the transmission may shift harshly, get stuck in one gear (limp mode), or the speedometer may read incorrectly. The fault is usually in the sensor, its wiring, or the connector, though internal transmission issues can also be responsible. On Mercedes-Benz specifically, this code is documented across 3 models.
What causes P0720 on Mercedes-Benz vehicles?▼
Common causes on Mercedes-Benz: Failed output (vehicle) speed sensor, Damaged wiring, connector, or corrosion in the sensor circuit, Metal debris on the sensor tip or damaged reluctor ring, Open or short in the signal circuit, Low or contaminated transmission fluid affecting components. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0720 on a Mercedes-Benz?▼
Repair costs on Mercedes-Benz range from $500 to $3,000, depending on the specific model and root cause.
Which Mercedes-Benz models have P0720 documented?▼
Au7o has documented P0720 on 3 Mercedes-Benz models: C-Class, E-Class, SLK-Class.