Originally posted by earossi
Can you explain the function of the SOV you mentioned above?
The egr needs some vac applied to it in order to open..
So, that plastic line up front that I mentioned earlier supplies some engine vac to the egr SOV . The SOV is simply an air flow valve [ in this case -vac flow] that opens when an electrical sig is sent to it from the ECU [ telling the valve to get some vac over to the egr.]
So, the system works like this :
ECU decides it is egr time , sends 12 volts over to the SOV. That opens SOV [ solinoid/coil/plunger arrangement all contained in SOV] and allows engine vac to pass through the SOV to the egr
[ through the small line you referred to before]...
So, this is how the ECU "CONTROLS" the working application of the egr ..
When the vac gets to egr , it pulls a diaphragm up and that opens the egr , allowing exhaust gases to recirculate back to the intake side of the engine.
That's about it....
The reason we apply eng vac to the egr valve with a hand pump to test it is b/c this ELIMINATES the CONTROL system of the egr circuit and narrows down the diagnosis from controls to EGR and plumbing..
It takes both to make the entire system work, and any one defect will throw the CE/EGR fault code...
A little more info for all interested.....
How does the ECU know it is time to CE/fault the system..????
Well. there is a little engine vac reader in the diagnostics system that , when ecu is sending its electric sig to egr , it also looks for a vac differential spec. If it see no change/little change, it knows something is not working..
So, is it just plugged at the tube ,not allowing flow, or egr sticking, or maybe the SOV ain't [ boy, I hate that word] got no vac to it from the broken line , or mabe the connector is unplugged ..ETC.
That is where you and common sense come to the rescue...
Again, the more you know of how things work, the easier they are to figure out and fix...