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since as mentioned the ECM "monitors the voltage on it's outputs" is there a possibility that ,I think it is the N249 vacuum solenoid valve under the intake manifold which opens the combi has failed electrically, thus since combi would be closed not allow the SAIP to activate since SAIP blockage might cause blower/motor to overheat. Sort of a failsafe ....valve not open ,pump no turn on
 

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Discussion Starter #42
I'd do this:
1) turn the key on (don't start the engine) and measure voltage between relay socket terminal 86 and ground. Should be ~12V. I doubt this is the problem.
2) if you can round up a piece of small gauge stranded wire, stick it in terminal 85 (with the blue/gray wire) and plug the relay in. Now, turn the key on (again, no start), then touch the small wire to ground for a few seconds. The relay should energize and the SAIP run. That proves the relay and SAIP both work.
Wow! Thanks for this writeup Fresco, I'll run through this tomorrow and hopefully we'll have hard evidence about what's working and/or what's not. I live just north of the SF Bay Area, it's been fairly mild lately, and the car's been started in early mornings, so I'm actually wondering if it's not the valve Cchief mentioned.

When I had it checked, the only code was "P0411 SAIP incorrect flow" or something like that, no mention of grounds, but now that you mention it, I'm reading about P0411 being a generic code.

Do you have VCDS? There may be a way to engage the SAIP manually via VCDS which could make trouble-shooting a bit quicker...
No, but I see there's a limited shareware version that can work with bring-your-own hardware. Is any of that stuff worth trying? Could be a last resort step? Buying the official stuff from Ross-tech looks like it would just be sinking too much money into this beater, and I'd be better off just taking her to a shop.

...is there a possibility that ,I think it is the N249 vacuum solenoid valve under the intake manifold which opens the combi has failed electrically
Well, looks like that'll be the next thing I look at if Fresco's process shows me the SAIP and relay work. Here's hoping it's not the valve itself, they're $75! Either way I'll be pleased to see anything fix this problem.
 

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I expect you could pickup a used valve fairly cheap at a junkyard.
 
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Beware the P0411 code is set by a performance test: during the SAIP test run, the O2 sensor reading should spike from the fresh air introduced to the exhaust. The code doesn't really single out one root cause.

For the O2 spike to happen:
  • The SAIP has to run, so the relay and fuse have to be good, and the SAIP to combi hose & pipe can't leak much
  • The combi valve(s) have to open, so they can't be carboned up and the vacuum lines to them can't leak and the N75 solenoid valve has to work.
The N75 valve is the least likely thing to fail. I've replaced the relay and the vacuum lines in my Passats and been fortunate with the combi valves, but many others have had to clean them. An expensive side effect of combi valves sticking open is exhaust flowing backwards in to the SAIP. Eventually enough moisture condenses in the SAIP to freeze in winter, splitting the SAIP housing. Argh!
 

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Discussion Starter #45
UPDATE:
Just ran out and went through these as descibed by Fresco and found an issue-

1) turn the key on (don't start the engine) and measure voltage between relay socket terminal 86 and ground. Should be ~12V. I doubt this is the problem.
2) if you can round up a piece of small gauge stranded wire, stick it in terminal 85 (with the blue/gray wire) and plug the relay in. Now, turn the key on (again, no start), then touch the small wire to ground for a few seconds. The relay should energize and the SAIP run. That proves the relay and SAIP both work.
I'm using the little red cen-tech digital multimeter harbor freight special set to 20 DCV.

-Measured voltage (with relay uninstalled) from socket terminal 86 plug to ground = 1.44
-Attached a small piece of electrical wire from socket terminal 85 (with relay installed) to ground = nothing happened

OK, so does this mean the ECU is not throwing enough power at the relay to run the SAIP?

The N75 valve is the least likely thing to fail. I've replaced the relay and the vacuum lines in my Passats and been fortunate with the combi valves, but many others have had to clean them.
The more I've read about combi valves, the more I'm suspecting they might be up to some trickery. I do get some exhaust smell every now and then, which others on this forum have tracked down to be combi valve related.

I'm planning to throw some new high temperature silicone vacuum lines on my car as this seems to be an easy $15 preventive thing, and will probably check out/clean the combi valve at the same time.
 

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FrescoGreen01.5 is the expert but my understanding is that pin 86 should always have 12V applied. The ECM pulls terminal 85 to ground to energize the relay and turn on the SAIP. So the good news is that it isn't probably a ECM problem. I think the problem is that you don't have 12V at terminal 86. There is a 40A fuse in the ECM box of course, but that is for the SAIP. There must be another fuse to supply 12V to terminal 86. If that is OK you'll have to start tracing backwards to see why there is no 12V present.
 

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You should not short any of those wires to ground, you could damage the ECU.

The Red/Black wire to the relay should always be 12V.
The Green/Yellow wire should be 12V when the ignition is ON. fuel pump relay is energised, (engine running)
The Black wire from relay to SAIP should be 12V when the relay is activated.
The Blue/Grey wire should be about 12v when ignition is on and relay is NOT activated, it should go close to 0V when the relay is activated.
Everything must be connected during above checks.
 

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Stop the presses!

Double checking the schematic, the green/yellow wire, relay terminal 86, is only hot when the fuel pump relay is energized. So, sorry, the engine has to be running. This is the same circuit that powers the O2 sensors, MAF, and several solenoid valves, all from fuse 34.
The ECM switches the negative side of the relay coil (blue/gray wire). The positive side of the relay coil is hot all the time, but only when the fuel pump relay is energized.
Ref: Bentley schematic 49/4, /5, /6.
 

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Discussion Starter #49
UPDATE:
Just ran out and checked relay terminal 86 with the car running. Got a cool ~12-13V! Thank goodness!

Took a quick peak at the vacuum lines that you can see easily. One of them looks a little rough, but can't tell if it's actually cracked or anything. They seem to all be the old braided hose type, so I'm just going to change them all anyhow.

Ordered some 3.5mm silicone a few days ago, should be here next week and once that process has taught me where the combi valve is, I can pull that off if the hoses don't fix anything.

Thanks for all your help guys! Will report back with success updates and/or more advice when I get stumped again.
 
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