1991 Mercedes-Benz 420SEL Air Pump Replacement Cost

Illumination of the check engine light would lead to retrieval of a fault code indicating a problem with the Secondary Air Pump. An abnormal noise from the pump would also indicate a problem.

Once the belt is removed or the electrical connector is disconnected, the pump is unbolted from its mount and the new pump is installed. If the pump is belt driven, the belt will then be installed and adjusted as necessary (replace the belt if an inspection deems it necessary). With an electric pump, the electrical connector should be checked for any damage and repaired as necessary prior to reconnecting it. Here are the full steps to replace each type of air pump: Electric Air Injection Pump

1. Disconnect the negative battery terminal
2. Remove any components that obstruct access to the electric air pump
3. Disconnect any air hoses and electrical connectors
4. Remove the fasteners that secure the air pump
5. Remove the air pump and install the new one
6. Secure the new air pump with its fasteners
7. Reconnect all electrical connectors and air hoses
8. Install any other removed components
9. Reconnect the negative battery terminal and clear any codes
10. Perform a Drive Cycle Test Drive to verify the repair

Belt Driven Air Injection Pump

1. Disconnect the negative battery terminal
2. Remove any drive belts that block access to the air pump
3. Disconnect any air hoses and electrical connectors
4. Loosen the air pump fasteners and remove the air pump
5. Install the new air pump and secure its fasteners
6. Reconnect any air hoses and electrical connectors
7. Install any removed drive belts and reconnect the negative battery terminal
8. Clear any codes and perform a Drive Cycle Test Drive to verify the repair

Excessive noise from the air pump indicates a problem that should be addressed. If a pump is damaged due to water intrusion determine the case and correct it. A service bulletin search could turn up a revised intake hose and/or baffle. When replacing an electric Air Pump always check the electrical connector for heat damage and repair or replace it as necessary.

An Air Pump can be damaged by water intrusion. When replacing a pump with this type of failure it is critical that all of the correct inlet hoses and baffles(s) are in place. A service bulletin search should be performed to check to see if revised parts of the Air Pump intake are available. High current flow can damage the connector of an electric Air Pump. When replacing the pump the electrical connector should be checked for heat damage and repaired as necessary.

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. Take note of any components that would need to be removed to replace the air pump. Make sure you have the tools and knowledge to remove and properly replace all that are required. Be prepared to check the entire Secondary Air Injection System for proper operation after replacing the pump. Special care should be taken to be sure all intake hoses and /or baffles are in place and on electric pump, the electrical connector is sound.