Mass Air Flow Sensor

This procedure covers the removal and replacement of the mass air flow (MAF) sensor on the 2019 Mercedes-Benz G-Class with the 4.0L twin-turbo V8 engine.

Warnings

Tools required

Parts

• Mass air flow sensor × 1 — A0009053603 or equivalent OEM
• MAF sensor O-ring seal × 1 — Use OEM specification

Preparation

1. Park the vehicle on level ground and apply the parking brake.
2. Turn off the ignition and remove the key from the vehicle.
3. Allow the engine to cool for at least 30 minutes if recently operated.
4. Open the hood and secure it in the raised position.

Procedure

1. 1

   Disconnect the battery negative terminal
   Locate the battery in the engine compartment. Using a 10mm socket or appropriate tool, loosen the negative terminal clamp nut and disconnect the negative cable. Secure the cable away from the battery terminal to prevent accidental reconnection during the procedure.
2. 2

   Locate the mass air flow sensor
   The MAF sensor is located in the air intake tract upstream of the turbocharger inlet, downstream of the air filter housing. On this twin-turbo V8, the engine typically uses two MAF sensors — one for each cylinder bank/air filter box. Verify which sensor(s) require replacement based on the diagnostic trouble codes, and confirm sensor location for each bank before beginning removal.
3. 3

   Disconnect the MAF sensor electrical connector
   Locate the electrical connector on the MAF sensor housing. Press down on the locking tab (typically red or gray) while pulling the connector straight away from the sensor. The connector may be tight due to the O-ring seal; gentle wiggling while pulling will help release it. Do not pull on the wiring harness itself.
4. 4

   Loosen the upstream intake clamp
   Determine the sensor mounting style. If the MAF is a plug-in unit inserted into the airbox/intake tube, remove the retaining screw(s) (typically Torx) and withdraw the sensor. If the sensor is an in-line housing clamped between two ducts, identify the upstream hose clamp (toward the air filter box) and loosen it: compress a spring clamp's ears with pliers or loosen a worm-drive clamp with a flathead screwdriver or socket, then slide it away from the sensor junction.nction.
5. 5

   Loosen the downstream intake clamp
   Locate the hose clamp securing the air duct to the downstream side of the MAF sensor (toward the turbocharger inlet). Using the same technique as the upstream clamp, loosen and slide this clamp away from the sensor junction. Keep track of clamp orientation for reassembly.
6. 6

   Remove the MAF sensor from the intake duct
   With both clamps loosened, gently twist the MAF sensor housing to break any seal between the rubber duct and sensor body. Pull the sensor straight out of the intake duct, being careful not to touch the sensor element inside. Inspect the sensor mounting area in the duct for debris, cracks, or damage. If the rubber duct shows signs of cracking or deterioration, note this for future service.
7. 7

   Inspect the old MAF sensor and O-ring
   Examine the old sensor for oil contamination, debris, or physical damage to the sensor element. Check the O-ring seal(s) on the sensor body for cracks, flattening, or deterioration. Compare the old sensor with the new unit to verify correct replacement part before proceeding.
8. 8

   Prepare the new MAF sensor
   Remove the new MAF sensor from its packaging, handling only by the plastic housing. Verify that the new O-ring seal is properly seated in the groove on the sensor body. Do not lubricate any seal with oil or petroleum-based products. Confirm the sensor's mounting method (plug-in with retaining screw versus in-line duct with clamps) before installation; if a seal requires lubrication, use only a manufacturer-approved silicone lubricant.
9. 9

   Install the new MAF sensor
   Align the new MAF sensor with the intake duct opening, ensuring proper orientation (the electrical connector should face the same direction as the original). Insert the sensor into the duct, twisting gently to seat the O-ring. Push firmly until the sensor is fully seated against the duct stop. The sensor should sit flush with no gaps visible between the housing and duct.
10. 10

    Secure the intake clamps
    Slide the downstream clamp into position over the junction between the sensor and intake duct. Tighten the clamp securely (if worm-drive, snug firmly but do not overtighten to avoid damaging the rubber duct). Repeat for the upstream clamp. Ensure both clamps are positioned squarely over the duct-to-sensor junction, not on the duct alone or sensor housing alone.
11. 11

    Reconnect the electrical connector
    Align the electrical connector with the MAF sensor terminal and push firmly until you hear or feel a distinct click indicating the locking tab has engaged. Gently tug on the connector body (not the wires) to verify it is locked in place. Inspect the connector boot to ensure it is fully seated with no gaps.
12. 12

    Reconnect the battery negative terminal
    Return to the battery and reconnect the negative cable to the negative terminal. Tighten the clamp nut securely using a 10mm socket or wrench. Ensure the connection is tight to prevent voltage drop or starting issues.

Reassembly

1. Reassembly is covered in the installation steps above, as this is a direct component replacement.
2. Ensure all intake clamps are tight and properly positioned to prevent air leaks that would cause false MAF readings.
3. Verify the electrical connector is fully locked before closing the hood.

Verification

• Start the engine and let it idle for 2-3 minutes. Listen for any air leaks (whistling or hissing sounds) around the MAF sensor area.
• Check for diagnostic trouble codes using an OBD-II scanner. The MAF sensor should register proper airflow values at idle (typically 3-7 g/s for this engine at idle, increasing with throttle).
• Test drive the vehicle and verify smooth acceleration with no hesitation or check engine light. The engine should respond cleanly to throttle input without stumbling.
• After the test drive, inspect the MAF sensor area once more for any signs of air leaks or loose connections.

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