In this guide, we will show you how to replace the air suspension control module (airmatic control unit) or M51 on a Mercedes Benz S-Class W221.
Replacing the airmatic control unit on a Mercedes Benz is relativity easy and takes about 1 hour.
This module was replaced because it was displaying a fault code for a faulty air strut ADS valve. The suspension was stuck in SPORT mode and ride quality was very rough.
Even after replacing the "faulty" strut, the code was still showing as current in the airmatic control module. Wires from air strut to airmatic moduel where tested.
Replacing the airmatic module itself fixed the problem.
What you will need
- Mercedes Airmatic control unit
- Used modules can be installed but ensure that you are using the correct part number.
Follow these steps to replace the airmatic control unit on a Mercedes Benz S-Class W221.
- Disconnect the negative terminal on the battery. The battery on W221 is located behind the rear seat and can be accessed via the trunk.
- Locate the airmatic control module in the passenger footwell.
- Grab one side of the carpet and pull it towards you, and push the carpet down.
- Remove the 10mm plastic nuts of the module frame, and pull down the metal plate.
- Using a 10mm socket remove the bolts on the metal bracket that is holding the control module.
- To disconnect the connectors from the control module, you just have to pull the connector lock and separate the connectors.
- Align the connectors to the control module and push the tab to lock.
- Install the metal bracket and tighten the bolts.
- Return the metal plate, and tighten the plastic nuts.
- Install the scanner and program the module.
Even though the module functioned properly without any programing, it is recommended to transfer the coding from the old control unit when possible.
- Make sure to disconnect the negative terminal of the battery every time you are performing a module replacement.
- Make sure to scan the vehicle before you perform the module replacement to have an idea about what codes are already in store before replacing the module, and what occurred after replacing the module.
- Back up the coding of the airmatic control module and restore to the unit.