Car: 1998 a4 2.8 Quattro

Hey there guys, I'm new to the forum, I usually frequent turbobricks.com but my wife and I just bought an A4 to enjoy. Hope to make good friends here and return the support the best I can.

Just yesterday, a CEL code p0411 popped up. I've read up a ton on it, but my problem is a bit different:

1. I already bench tested the pump itself... it works great

2. I've checked and tested the relay... no problem there

3. The fuse is ok too.

The problem I am having is that it will not come on in the morning. It seems like there is no signal from the ECU, car, whatever, to turn the device on.

You may have noticed my last post about my hard start issues in the morning. Could these two things be related since from what I hear the SAI pump only comes on when cold? I've already changed out the coolant temperature sensor, but no difference.

I'd like any advice you guys can offer. Also if anyone knows where I can flash the ECU to set the SAI sensor to ready, that's good info too... but I'd rather solve the problem than bypass it.

Cheers and thanks!

(P.S) ... Between my front bumper and radiator, with the hood open, there is a sensor in from of the radiator of some sort with two wires going to it. The sensor seems broken or missing. The wires and plug is plugged into a short bit of plastic that seems incomplete. Anyone know what this is and what it does in this vehicle? Temperature sensor? Could it be related to my issue?

 

The sensor in front of the radiator (usually held by the power steering cooler lines) is the ambient temperature sensor. Makes sense that the car would act like it's cold if the temp sensor is gone.

 

I appreciate your reply, however the car acts like it thinks it is warm in the morning, not cold, hence the hard start.

 

Have you replaced your vacuum lines? I'd start there. Chances are that'll fix your problem.

 

The issue is, the pump is not getting power when it needs it despite the fuse and relay being good. I don't understand why changing the vacuum lines would do anything. The issue isn't that the system leaks, it is that the pump won't even turn on even though like I said, the pump, relay and fuse are all fine when bench tested.

 

I'm focusing on fixing the p0411 code. If you fix that, maybe it'll indirectly fix the SAI pump "problem". (the pump is freaking annoying and I'd like to get rid of it).

I fixed my P0411 code when I replaced my vacuum lines. Thats why I asked if you did it. It can't hurt either.

"The P0411 has to do with the SAI pump on a cold start. Incorrect flow indicates that the extra air isn’t making it to the front O2 sensor. It doesn’t have anything to do with the PRV valve (the round black valve on the back of the valve cover). On a cold start the N112 valve located underneath the intake manifold sends a vacuum signal to the combi valve (the silver metal disc valve at the back of the motor). The vacuum causes the combi valve to open. At the same time the SAI pump starts to run and injects the extra air into the exhaust port underneath the combi valve. This extra air serves to bring the catalytic converter up to temperature faster.

You need to examine both sides of the system. First make sure the vacuum line is intact from the N112 to the combi valve. Next make sure the air injection lines are intact from the SAI to the combi valve. You probably have a break on one side or the other."

 

And if the ambient temp sensor is shot, definitely replace it with a working sensor.

 

Does the ambient temp sensor do anything aside from telling you the outside temp?

 

Swapped ecu out and now the pump comes on in the morning and code is gone. Sheesh, right?

 

That's weird..