NTK 27057 Air / Fuel Ratio Sensor - Upstream

NTK Direct Fit Air/Fuel Ratio Sensor

NTK 27057 is a direct fit heated air/fuel ratio sensor built for specific Mercedes-Benz applications that require an upstream OE-style replacement. It uses a 5-wire design with a 29.5-inch harness and 18 mm thread diameter for a precise match to the original sensor layout.

As part of NTK’s Direct Fit 5-Wire A/F Sensor line, this sensor is engineered for exact application coverage and OE-equivalent fit, form, and function. NTK applies ceramic sensor manufacturing expertise and extensive production testing to support consistent signal performance and reliable emissions control service.

Key Features

• Direct fit heated air/fuel ratio sensor for upstream placement
• 5-wire configuration for OE-style signal and heater control
• 29.5-inch wiring harness length
• 18 mm thread diameter with 0.38 thread length
• Specific fit for select Mercedes-Benz diesel applications
• OE-equivalent design for factory-style replacement

Detailed Description

NTK 27057 is an upstream air/fuel ratio sensor for select Mercedes-Benz models, including the Mercedes-Benz GLE300d, E250, GLK250, ML250, and S350. This part number is built for vehicles equipped with one upstream sensor only and is listed as a direct fit replacement for the original sensor location. If you are replacing a Mercedes-Benz upstream A/F sensor and need an OE-style match, NTK 27057 provides the correct connector and sensor configuration for the application.

This part cross-references Mercedes-Benz 0075421618 for the same application.

What This Sensor Helps Address

• Check engine light related to upstream air/fuel ratio sensor performance
• Incorrect fuel trim readings from a failing sensor
• Slow or unstable sensor response during closed-loop operation
• Emissions control faults tied to the upstream sensor circuit
• Driveability issues caused by inaccurate exhaust oxygen feedback

Installation Notes and Tips

• Verify the vehicle is equipped with the upstream sensor configuration listed for this part.
• Confirm connector style, thread diameter, and harness length before installation.
• Inspect the exhaust bung and wiring route for heat damage or corrosion before fitting the new sensor.
• Use the correct sensor socket and follow factory torque specifications during installation.
• Clear diagnostic trouble codes and verify live data after replacement.

Quality Assurance

NTK manufactures oxygen and air/fuel ratio sensors with OE-level application coverage and production testing to help meet or exceed original equipment specifications. The brand’s sensor-focused engineering and ceramic manufacturing background support consistent quality for emissions control service.