austinado16

^Update. CEL back on....EGR low flow. Damn it.

islingtonaudi

Try this #: 51731470035

kday

How does the ECU detect low flow?

austinado16

Unless I've missed the info in the Bentley somewhere?

This is one area where Bentley sucks. "It/They" assume the user has had all the up to date dealership training, so the only thing they provide is very cursory test proceedures and "If/Then" methods.

My guess is that the EGR system doesn't get activated until the coolant temp comes up and the fuel injection goes into "closed loop." Then, because one side of the EGR solenoid is hooked to manifold vacuum, it is kept "closed" at idle when manifold vacuum is high (when the throttle plates are closed. Once throttle plates are opened and manifold vacuum drops off to near zero, then vacuum from the throttle body takes over. At this same time, the computer sends a pulsing signal to the EGR solenoid (which makes it open/close fast...hence the ticking)and throttle plate vacuum is sent directly to the EGR valve, opening it. Finally, the EGR temp sensor down below the throttle body looks at how hot the incoming exhaust gasses are and this tells the computer that the EGR valve is open.

I don't know if the computer is looking for a certain temp range from the EGR temp sensor, or if it's looking for a certain temp in a certain time frame. Then, if it doesn't "see" this, it throws the code..."hey, you're not getting good exhaust gas flow through your EGR valve, pal."

Anyway, that's my theory. Anybody know for sure? It would make a nice little write up for the FAQ's.

kday

<a href="http://www.boost-instruments.com/egrcodes.png">EGR temp code page from Bentley</a>

I read that as the conditiosn for EGR activation are as described for the code -- part throttle highway cruising.

Are you getting the "EGR temp sensor implausible" code also, or just the low flow code?

I don't know why the EGR solenoid would click at idle. That seems weird.

austinado16

My EGR solenoid doesn't tick at idle. It ticks when you bring the rpms up and hold them at cruise speed.

In the section of Bentley that talks about testing the signal to the EGR solenoid, it says you should get a blinking LED signal. That tells me the computer is switching the solenoid off and on repeatedly.

kday

Have you considered connecting a vacuum gauge to the EGR solenoid vac. port and monitoring it?

austinado16

I've got all kinds of flow through the EGR valve itself and throught the port in the intake. So, I've either got a bad solenoid, or a bad EGR temp sensor. Or maybe no, or low vacuum going to the solenoid from the throttle body source. Just need to prove which.

Bmthorn

My friend who told me to get it bought it from the same dealer for $6. I got the part number from this picture.

<img src="http://pictureposter.audiworld.com/43547/bmw_vacuum_hose.jpg">

kday

P/N N203551

Haven't tried it on the A6 but it fits the hose barbs on the AAN intake.