Secondary Air Monitor Failure


I have a 2003 bmw 330xi with 136k miles that wont pass smog because the secondary air monitor wont complete. At this point im stumped and there’s not check engine codes set or pending. I replaced all vacuum lines, verified the vaccum switch controlling the system works and holds pressure. Verified the valve works and even replaced it just to make sure. Air pimp works and stays on for required time. I even manually opened the valve with a vaccum pump and still nothing. Someone mentioned that a lazy O2 sensor could be the issue but all other monitors complete with no problems within 15 mins. Any ideas?


Are all the other monitors complete?


yup all complete


I am going to speculate out of ignorance here. First, I have never heard the word “complete” used in this context, but I am guessing that the battery was disconnected, and the computer had to go through re-defining its calibration constants for all the sensors over a series of drive cycles, but it was unable to define a calibration constant for the hot wire anemometer on the secondary air.

I think that you are probably getting current to the sensor to heat it up. If you weren’t, the computer would set a code for no signal or no air flow, even it it could not calibrate. You could check that, but you probably have voltage to the sensor.

That leads us to the theory that you are getting a flow signal that is within bounds, but not consistent enough for the computer to set a calibration constant. I would first determine if there is an electrical ground for that sensor (other than computer ground) and make sure that is clean. Actually, make sure all electrical connections are clean. Then I would check for air leaks and foreign objects in the air pathway. If I found no problems there, I would suspect that the check valve is gummed up or failing and not opening all the way every time.

I live in a dry climate and have not had any trouble with grounds yet on my e46s, but on the older e36s, grounds were found to be the culprits in several thorny electrical mysteries.



live in California, and if all monitors except air injection had run to completion, then the car would be allowed to be smogged, and would pass . . . assuming the check light isn’t on, no codes commanding the light to come on, no emissions components missing, no visible smoke, no tampering, etc.

I might add that California probably has among the most stringent laws regarding emissions. And it sounds like where you live, they’re trying to trump that

So I’m a little confused . . .

Is your car actually FAILING the smog check, due to the incomplete monitor?

Or does the guy refuse to TEST it, because of the incomplete monitor?

I’m kind of wondering if the guy is allowed to test it, but won’t . . . because of his testing station’s “score” . . .

In California, you’re allowed to have one incomplete monitor, just as long as it it’s catalytic converter.

Does your state require ALL monitors to be complete?

What state are you in, BTW . . . ?


There should be a steel line from the vacuum switch to the exhaust manifold where the air is injected into the exhaust. Check that line for obstructions and also check the passage in the manifold where that line screws into. You need a clear path all the way from the pump to the exhaust gases. A little carbon build up in the exhaust manifold can block the air.


There’s no code or CEL for the monitor status. For the monitor to complete a certain drive sequence has to take place. If you do that and it still won’t complete, it will flag a code for the reason. But you haven’t completed the drive sequence yet. That’s my guess anyway.

A BMW dealership should be able to tell you what the drive sequence is for that monitor. It’ll go something like "drive to at least 35 mph, engine at normal temperature, then to at least 50 mpg, then back to idle rpm, there may be a requirement for the fuel tank to make a transition too, like from half to below 1/3 full. Like I say, the BMW dealership shop will be able to tell you.


A code will NOT set if the monitor hasn’t run to completion

That is how people trick their way through smog inspections

if they KNOW they have a specific code being set, and it keeps coming back, they get all the other monitors to set, but purposefully prevent the monitor that’ll set the code from running to completion

For example, if you have a certain evap code, you figure out what the criteria for running the monitor is. And then you make darn sure you DON’T meet those criteria

Then you show up at the testing station will all monitors complete EXCEPT evap

AFAIK . . . the smog tech is obligated to test the vehicle. But it could still fail for tampering, missing components, etc.


In California the only other monitor that can be incomplete and still pass is the EVAP monitor. Ive completed the drive cycle numerous time with no problem completing all the other monitors except the secondary air. All vacuum lines were inspected and replaced along with the valve. I also ran seafoam through the system so that shud have cleared andy junk build up


If the computer thinks you’ve completed the required drive cycle for the air pump test it would say so, and post a diagnostic code if it found something wrong. Maybe there’s something unrelated to the air pump test itself that is registering inaccurate results and making the computer think you haven’t done all the driving maneuvers it wants to see, like a problematic odometer function, vehicle speed sensor, gas tank fill level sensor, gear shift sensor, etc.

One off-the-wall idea, admittedly from a diy’er who knows nothing about BMW’s or air injection pumps – I’m surprised a 2003 BMW has one in fact, I thought those had disappeared as obsolete technology years ago – but for the air pump to inject air into the exhaust, air has to enter the pump somehow. And there’s probably an air filter involved. Maybe that pump inlet path is clogged.


The issue could be that the air temperature in your area is not cold enough to cause the air pump to be commanded on. You might have to take it for a drive at 0-dark-30. Maybe the ECTS (engine coolant temp sensor) is not accurate at the low end so the PCM thinks the engine hasn’t cooled off. Some of these things are things the computer would not know are in error.