P0731 on Mercedes-Benz
Gear 1 Incorrect Ratio
P0731 on Mercedes-Benz vehicles indicates gear 1 incorrect ratio. Au7o has documented this code across 4 Mercedes-Benz models — most commonly on C-Class, CLS-Class, GLS. This code means the Transmission/Powertrain Control Module detected an incorrect gear ratio in 1st gear. The module compares input (engine/turbine) speed to output shaft speed; when the car is commanded into 1st but the calculated ratio doesn't match the expected value, P0731 sets. This points to slipping, an incorrect shift, or a hydraulic/mechanical problem rather than just an electrical fault. You may feel slipping, harsh or delayed engagement, or the transmission may go into a limited 'limp' mode. Typical repair costs on Mercedes-Benz range from $150 to $4,000, depending on the specific model and root cause.
Common Causes of P0731
- •Low or degraded/burnt transmission fluid
- •Slipping clutch packs or worn friction components
- •Stuck or faulty shift solenoid affecting 1st gear
- •Internal hydraulic leak / valve body fault
- •Worn or failing torque converter
- •Faulty input or output speed sensor
- •Mechanical wear (planetary gears, bands) inside the transmission
P0731 on Mercedes-Benz by Model
Mercedes-Benz C-Class(1 issue)
- 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 CLS-Class(1 issue)
- 7G-Tronic Transmission Valve Body Failure2005-2014
The 722.9 7G-Tronic automatic transmission in CLS models suffers from valve body conductor plate failures. The electronic conductor plate controls shift solenoids and develops internal short circuits or loses communication, causing harsh shifting, getting stuck in limp mode, or refusing to shift out of park. This is one of the most common transmission failures on Mercedes vehicles of this era.
Mercedes-Benz GLS(1 issue)
- 9G-Tronic Harsh Shift2017-2023
The 9G-Tronic nine-speed automatic exhibits harsh low-speed shifts and hunting between gears on inclines. The transmission software struggles to select the optimal gear among nine ratios, particularly noticeable in stop-and-go traffic.
Mercedes-Benz Metris(1 issue)
- Harsh Shifting and Delayed Engagement in 7G-Tronic Transmission2016-2023
The 7G-Tronic automatic transmission in the Metris exhibits harsh shifts, particularly the 2-3 and 4-5 upshifts, along with delayed engagement when shifting from park to drive. The issue worsens as the transmission fluid ages and the valve body accumulates debris from clutch material.
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View P0731 across all makes →Frequently Asked Questions
What does P0731 mean on Mercedes-Benz?▼
P0731 stands for "Gear 1 Incorrect Ratio." This code means the Transmission/Powertrain Control Module detected an incorrect gear ratio in 1st gear. The module compares input (engine/turbine) speed to output shaft speed; when the car is commanded into 1st but the calculated ratio doesn't match the expected value, P0731 sets. This points to slipping, an incorrect shift, or a hydraulic/mechanical problem rather than just an electrical fault. You may feel slipping, harsh or delayed engagement, or the transmission may go into a limited 'limp' mode. On Mercedes-Benz specifically, this code is documented across 4 models.
What causes P0731 on Mercedes-Benz vehicles?▼
Common causes on Mercedes-Benz: Low or degraded/burnt transmission fluid, Slipping clutch packs or worn friction components, Stuck or faulty shift solenoid affecting 1st gear, Internal hydraulic leak / valve body fault, Worn or failing torque converter. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0731 on a Mercedes-Benz?▼
Repair costs on Mercedes-Benz range from $150 to $4,000, depending on the specific model and root cause.
Which Mercedes-Benz models have P0731 documented?▼
Au7o has documented P0731 on 4 Mercedes-Benz models: C-Class, CLS-Class, GLS, Metris.