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Secondary Air Sensor Not Ready--need some help diagnosing
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menko
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PostPosted: Thu Jun 30, 2022 12:40 pm    Post subject: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

Hi everyone,

Last week my 2003 VR6 Eurovan failed CA smog. On a 100F day, I drove the van 2 miles to the smog place and parked it. They hooked up their scanner, turned the car on and walked over to say "your Check Engine light is on." I was pretty mystified, as I had just taken the van on a 1200 mile trip the previous weekend and the CEL wasn't on, but I have had a P0171 code flash maybe once every year or so at the end of a long trip when we were heavily loaded. So I cleared the code which of course put all my OBD sensors to not ready.

After several day of cold start cycles, I still cannot get the Secondary Air Monitor to get ready. I pulled out VCDS and ran an autoscan, only to discover my ECU is only reporting back from the 01 engine, and timing out on everything else. So I wasted 2 days trying to get that working, to no avail. I am in the weeds trying to determine how to check the vacuum lines and just need some help.

What is the Readiness Sensor checking for and failing to find? I wasn't sure how to test the solenoid, but I figure if that isn't working, the SA pump still comes on, but the combi valve never opens.

Steps I've taken so far:
    Started the van cold, verified the SA pump is running for the first 60-90 seconds)
    Checked the pump for cracks (none)
    Pulled the hose from SA pump and found no water
    Ran Output Tests with VCDS: Pump goes on and off just like with the car
    Secondary Air Injection Solenoid Valve (N112): I don't hear it clicking or anything with VCDS
    Secondary Air Pump Relay (J299): Pump cycles on and off when testing


So I'm now stuck trying to deal with the vacuum lines on the solenoid and combi valve. They look ok but are rubber at the ends and slimmed down plastic in between. The rubber on quick inspection is old and crumbly, which I'm afraid will break if I try and remove them. I'm not sure if I can just replace the rubber ends, or the entire lines, and need some advice on this part before I try to remove them for testing.

Based on my VCDS testing and a look at the system online, it seems I need to first verify that the solenoid is opening to let vacuum from the manifold activate the combi valve, and if that is working verify the Combi valve is opening and closing correctly. If I can get the combi valve hose off, and use a vacuum pump on it while running the car, I should be able to disconnect the SA hose to the combi valve and hear that it is opening and closing to the exhaust.
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gesoffen
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PostPosted: Thu Jun 30, 2022 2:02 pm    Post subject: Re: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

menko wrote:

So I'm now stuck trying to deal with the vacuum lines on the solenoid and combi valve. They look ok but are rubber at the ends and slimmed down plastic in between. The rubber on quick inspection is old and crumbly, which I'm afraid will break if I try and remove them. I'm not sure if I can just replace the rubber ends, or the entire lines, and need some advice on this part before I try to remove them for testing.


Off the top of my head, I can't help with the VCDS readiness issues.

Regarding the vacuum hoses, I would suggest vacuum testing them and see if they hold for a period of at least several minutes (~10). If they visually appear old and crumbly, they are likely leaking (vacuum hoses tend to always "look" in better condition than they actually are).
Regarding your specific areas of concern:
- the rubber ends with the plastic in between is just that. With a pick or a small screw driver (think jewelers or eyeglass size), you should be able to gently separate the rubber hose ends from the plastic tubing (as well as other fittings) and remove. Over time, they've developed a slight adhesion so the pick/screw driver will be needed to help get them off. Be patient, be gentle.
- you can replace with similar diameter lines from your FLAPS, though if the original german braided lines have lasted ~20yrs, I'd get a new length of the german stuff and trust it to last another 20yrs.
- the small plastic tubing was there to help more cleanly route lines throughout the engine compartment (molded bends, less chance of kinks, thinner than the vacuum hose). Also probably a cost/emissions warranty measure by VW. They can be reused. If you have isolated damage, you can simply splice them with a small length of rubber vacuum lines. If sections are completely destroyed or missing, you can replace with a longer section of the rubber hose.
- I recommend you also carefully inspect the vacuum line from the brake booster to the drivers side of the cylinder head (a bit larger, roughly 1/2" diameter line) as well as the check valve and tees on that line. Those are frequent failure points.
- Unless already done, it would be worth checking the condition of some of the other rubber bits (coolant hoses, oil cooler hoses, etc.). Visual check at least with a quick squeeze to see if they are firm (good) or gummy/spongy (not good). This is especially true of the oil cooler hoses.
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menko
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PostPosted: Thu Jun 30, 2022 3:19 pm    Post subject: Re: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

Amazing, thank you so much for taking the time to walk through that with me. Knowing I can separate those out I'm far less afraid of disconnecting those hoses.

I have replaced the brake booster line a few years ago after it had cracked, but I'll go through and check the others. Once I have the lines off, I can just use the mityvac pump and do some tests. Let me see what happens tonight and I'll post back. This would make it much easier to test the combi valve without taking it off Wink
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menko
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PostPosted: Sun Jul 03, 2022 2:28 pm    Post subject: Re: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

Ok so I'm sort of at an impasse to figure out why I can't get the secondary air monitor to come ready.

I have tested all parts of the system and they are working as expected as far as I can tell.


[list=]solenoid lines have been replaced, it opens and vacuum comes from the manifold
VCDS output tests on solenoid trigger open/close and I have blown air through it during the cycle and confirmed it opens/closes
Combi valve is clean, opens at start up, and closes on the warmup cycle
Secondary air pump is pushing air hard at startup, and stops in the 60-90 second time frame after the combi valve closes [/list]



I can't figure out what else the readiness monitor would be detecting to say the 2nd air isn't ready. I can't get it to pass smog without the readiness code, and have been through atleast 10 startup cycles trying to get it to come on.

What am I missing or not understanding that I need to look at? Here's a quick startup video I took today.



Link



Thanks, I'm sort of at wits end here as it *seems* to my uneducated self that nothing is malfunctioning in the SAI and so why the heck can't it become ready?

Appreciate any help!
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Abscate Premium Member
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PostPosted: Sun Jul 03, 2022 3:01 pm    Post subject: Re: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

You have to complete a drive cycle, not just startup cycle.

The T4 isn’t a hard car to get ready compared to many.

Gas tank about 1/2 full
No AC
Smooth , gentle acceleration
Don’t exceed 60 mph
No full throttle

30-50 acceleration, followed by a few minutes idling
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menko
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PostPosted: Sun Jul 03, 2022 6:12 pm    Post subject: Re: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

ok I mean I have driven it all around and on the freeway, but probably exceeded 60mph. I'll give that a try tomorrow and see. I have reset the ECU before and never had trouble with any of the codes getting ready, so after several days of driving it and cold starting it I started in the SAI journey. Thanks for the help and I'll report back.
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menko
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PostPosted: Wed Jul 06, 2022 12:51 pm    Post subject: Re: Secondary Air Sensor Not Ready--need some help diagnosing Reply with quote

Abscate wrote:
You have to complete a drive cycle, not just startup cycle.

The T4 isn’t a hard car to get ready compared to many.

Gas tank about 1/2 full
No AC
Smooth , gentle acceleration
Don’t exceed 60 mph
No full throttle

30-50 acceleration, followed by a few minutes idling


Thanks Abscate! The 30-50 without going over 60 did the trick. Finally got it ready and CA smog is passed for another 2 years. Thank you so much!
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