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Discussion Starter · #1 ·
So I started a conversation with Steve from Chicago.. and he suggested I start a forum up about it. Here is the conversation and I hope somebody can take it somewhere from here and also offer some advice or past experience with the issue. Thanks


I see you're somewhat of a residential expert and I believe I have reached a point of needing some serious advice. I have had the whole group of codes. P1423, P1411, and intermittent o2 sensor codes that I believe are unrelated and no longer showing up.

I have replaced the following
-PCV tubes
-Vacuum Lines
-Combi Valves. Yes both of them and it was painful.

I have done a vagcom test and the guy pretty much told me he didn't know why i was still getting that code because it wasn't anything with the malfunction of a particular point in the system, which confirmed what I believed to be the combi valves. But now after about 5 cold starts the code came back, but all by itself this time. Just P1423.

Is there something I'm missing?

I was PM ing you simply because there is a clutter of P1423 forums that essentially are rudimentary compared to the extent of the issues I have fixed and I don't want to Bump a forum that is painstakingly long and scatterbrained.

Thanks for any help

-Dan in Tacoma

Steves reply:

The SAIP system runs at cold start. It runs for 60~100 seconds. During the cycle the pump runs and both combi valves open. The purpose is to inject fresh air into the exhaust. The extra air helps the rich cold-start exhaust burn the extra hydrocarbons. It also helps get the CAT up to operating temperature faster.

The ECM monitors the health of this system by running a test on it. Sometime after the cold start sequence and after the O2 sensors are fully hot and on-line, the ECM will cycle the system on for a short time and monitor the O2 sensors. It expects to see an increase in the amount of oxygen in the exhaust stream. If it doesn't see what it expects, that's when you get a code for insufficient flow.

You're bank 2 is no longer popping this code but your bank 1 still is. Check for reasons you'd not have proper flow on the passenger side bank. Verify that combi opens/closes. Verify the air path from the pump to that side combi is intact.

What test did they guy helping with vag-com do?

Quote Originally Posted by threeinthebush
They ran a test where they started each function individually to see if there was failure at any point in the system. IE turning on just the SAIP, n112 valve, 40 relay and listened to the pump to see if it was abnormal. The next one I was going to look at is the replacement of the rivets on the pump to make sure extra air isn't leaking out
When the pump starts up.

So really if an o2 sensor passes the "o2 sensor test" and is reading the levels that pass it doesn't necessarily mean it will pass the p1423 portion that relies on the o2 reading post cat? That sound confusing but I'm wondering if it's possible that my o2 sensors not being 100% could contribute to the p1423 code and not an individual sensor code.

OK, then they tested each link in the chain. I don't know about the O2 sensor. That's a good question. Can it be marginal and work fine for one function but fail at the other.

The riveted pump housing is a good thing to check. One other obscure cause I read about one time was the ports in the head (where the combi delivers the airflow) had clogged up and blocked airflow. I imagine you could try testing for this without taking too much apart. Use a hand vacuum pump to open the combi valves then blow into the pipe supplying the left head. Then blow into the pipe supplying the right head. Both paths should allow a similar amount of flow with a similar amount of effort. If one is blocked, you've found the problem.

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Just for kicks, check what your vacuum is at idle somewhere on the intake manifold, and also, what it's at on the solenoid (unplug its connector and its outlet port and activate it with jumper wires from the battery). Before you do this, check the solenoid's resistance. I don't have the specs in front of me, but they are usually about 18-27 ohms.

It might also be that the air path from the blower to the changeover valve (combi) is somewhat obstructed, or has a very small leak enough to trigger the code.

A couple of things to consider -- they helped me when I had to deal with this a while back.

You can pretty much test and troubleshoot every part of the system much more quietly with the engine off, if you have a vac pump of some kind (the V6 has a vac reservoir as well, which might help some). You can jumper actuators, and electrical components (unplug their connectors before you do this).

If you remove the spark plugs and plug the exhaust, you can see how much airflow you are getting from each bank. (it is a bit tricky, you might have to turn the crankshaft by hand to open the exhaust valves on one cylinder only). You will be going by feel here, and it's not a very reliable diagnostic for slight differences, only for big obstructions.

If you want to test for air leaks on the path from the blower all the way to the combis, you can turn on the blower briefly, and spray soap water on the various connection points, and look for bubbles.

Beyond that, I don't have any suggestions for an O2 sensor diagnostic other than checking the fuel trims (block 32 onwards). It's hard to accept that only the SAI system could expose a borderline O2 sensor, but, who knows, they are old enough.
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