While the pictures in this guide are from an S-Class, these instructions will help you learn how to change a catalytic converter on Mercedes-Benz C, E, CLK, CLS, GL, ML, GLK, and other models required with V8, V8, and V12 engines.
What you will need
Allow the car to cool down. The exhaust system can get very hot and may remain hot even after the engine cools down. Jack up the vehicle front and back on the side that you will be changing the catalytic converter. Make sure to secure the vehicle with jack stands. Set the parking brakes and block the wheels on the opposite side. Do not get under a vehicle that is not secured with jack stands.
- Remove all the splash shields from under the engine. The splash shield is held in place with several 8mm screws.
- Disconnect both oxygen sensors cables. We were able to disconnect both the upstream and downstream from the top. In some cases, it is easier to disconnect the downstream from under the car.
- Spray penetrating oil on the bracket at the middle of the vehicle and let it penetrate the bolt for at least 15 minutes or longer. Loosen the nut using an E10 socket and slide the bracket off.
- Remove two 10mm nuts. Remove the bracket from the car.
- Remove the two 13mm bolts at the flange above the catalytic converter.The upper bolt was easier to remove from above the engine. The lower bolt we were able to remove from under the vehicle. To access it, we had to use a couple of 8" ratchet wrench extensions.
- Carefully lower the catalytic converter and remove it from the vehicle.You may have to remove the oxygen sensors to make room to pull down the old catalytic converter. In this S-Class, we were able to remove the passenger catalytic convert with the oxygen sensors still attached. Once you have the catalytic converter of the vehicle, it is a lot easier to remove the oxygen sensors.
- Reinstall the catalytic converter in reverse order.
Replacing a Mercedes cat converter is relatively easy. The main challenge is when a bolt refuses to come off, and that happens quite a bit. What we have found to be very helpful is to spray penetrating oil on the bolts that need to be removed a couple of times the night before you plan on replacing the catalytic converter.
If you have a new OEM catalytic converter, the procedure is very straightforward and can be completed in your driveway. Just make sure to secure the vehicle with jack stands, as you will spend quite a bit of time under the car.
When it comes to installing a universal catalytic converter, it may be better to leave it to the professionals. Installing a universal catalytic converter may require cutting the old cat converter and welding. We would recommend finding a muffler shop in your area and have them install the catalytic converter. We have installed universal catalytic converters on Mercedes-Benz in the past, and they performed just as well as the OEM cat.
The average cost to replace the catalytic converter at a Mercedes-Benz dealership is around $1400-$1800.
A less expensive alternative is to find a muffler shop that will install a universal catalytic converter. The cost to install a universal catalytic converter ranges between $400 and $800. A universal catalytic converter works the same as the OEM cat converter, and all the oxygen sensors still work properly.