What is the fan that runs by itself in the front of the intake system and connects to the egr Valves 2001 S430, fan was running after shut off for about an hour two tubes do connect to the egr valves from this fan does anyone know what it is and why does it run by itself with engine warmed up and is shut off???? / Had someone look at my 2001 S430 and they said the relay stuck and cuased the secondary air pump to burn up have anyone heard of this problem before and how many electrical problems can i expect with this BENZ / am still ASE cert. have been in the service industry fro over 30 years. need some help here. thanks

I would be at a loss with the original post. From the reply, I agree you are probably talking about the secondary air blower. It does not blow into the EGR though. The EGR takes exhaust and allows it into the intake. The secondary air pump blows air into the exhaust near the valves. Two entirely separate systems dealing with different emmissions issues.

Secondary air is only used during warm-up to burn excess hydrocarbons in the richer cold running mixture. It also works before closed loop as excess air in the system would affect the mixture if the O2 sensor was working. Its main purpose is cleaning the exhaust and warming the O2 and cat.

The EGR on the other hand is used especially when hot to lower the burning temp by introducing an inert gas (all O2 has been previously burned) to displace air containing O2 and cool the flame. This is specifically used to reduce the formation (oxidation) of oxides of nitrogen NOx.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician