1994 Mercedes-Benz S420 Air Injection System Check Valve Replacement Cost

Most commonly an illuminated check engine light would lead to retrieval of a fault code indicating a problem with a Secondary Air System check valve. A suspect valve would then be tested for proper operation, unrestricted flow in one direction and no flow in the other. Heat damaged Secondary Air Injection hoses and/or components would also lead to inspection of the check valve(s) for proper operation.

A Secondary Air System Check Valve will either screw directly onto a pipe connected to the exhaust system or bolt onto a metal flange that is part of the exhaust system. On some models, various components my need to be removed to gain access to the valve. A bit of penetrating oil on the mounting threads or bolts can greatly aid in removal of the old valve.

Care should be taken when working around hot exhaust system components. Threads should be treated with a penetrating oil prior to removing an AIR System Check Valve. It may be a bit easier to remove a check valve when the engine and components are warm as opposed to stone cold. Always try and confirm you have the correct part prior to removing the old one. Additional parts of the Secondary Air System can be damaged if the engine is run with a failed check valve that is allowing hot exhaust gases to pass through it.

Rust can develop on exhaust system components making disassembly difficult. Penetrating oil should be used on threads prior to removal of any components. Care should be taken when working around a hot exhaust system.

Repairing your own car is an extremely rewarding process that can also save you money. But before you dive in, it’s important to be sure the issue has been properly diagnosed. Seemingly obvious symptoms can lead the inexperienced down a rabbit hole of replacing parts that don’t fix the problem. Proper diagnosis can save more money than guessing at what’s broken! If you're unsure you have the right tools or experience to diagnose a problem, consider reaching out to a RepairPal Certified Shop. Care should be taken when working around a hot exhaust system. Take note of any components that would need to be removed to replace the check valve. Make sure you have the tools and knowledge to remove and properly replace all that is required.