E39 Secondary Air Pump -- Fault Codes P0491, P0492

[napalirick]

For a 2002 530i I have been battling a "Service Engine Soon" ("SES") light since February. Fault codes are P0491 and P0492 (Secondary Air Flow Insufficient). I've replaced the secondary air pump, secondary air pump valve, the one way electronic valve. Have also checked the relays, fuses, hoses. All appear to be okay. I'm getting vacuum at the output of the secondary air pump at start up when the engine is cold and you can hear the pump running. My mechanic says at least one of the catalytic converter(s) (there supposedly are two on the car) is bad.

When I turn off the SES light with the OBD-II tool, the light comes back on the same day or after a day, but only after a cold start up. The same two fault codes show up.

My car is due for emissions inspection in July. Merely turning off the SES light without putting the car through its drive cycles will not allow it to pass inspection. Unfortunately the SES light comes on before too long.

Is the bad catalytic converter the cause for the SES light to come on?

Any other suggestions?

Thanks.

[MalakaSpeed]

i got the same problem i replaced everything and still have this stupid light on.

[TyroneShoe]

I have no idea if this is safe at all but I'm brainstorming a little. If it is still registering insufficient air flow (and that really is the problem) you could try looking at the pipe that connects the valve to the exhaust system. Perhaps it got blocked fully or partially (enough to register the code). Perhaps unbolt the valve and 1) check that the valve is opening and air is blowing through on engine start and 2) check to see if exhaust backs up through the pipe. Like I said, it may be totally unsafe to do this so I'm not "recommending" anything, just thinking in print.

[MaxVQ]

I'm getting vacuum at the output of the secondary air pump at start up when the engine is cold and you can hear the pump running. My mechanic says at least one of the catalytic converter(s) (there supposedly are two on the car) is bad.

Is the bad catalytic converter the cause for the SES light to come on?

Vacuum at the output of the secondary air pump???? You should have a slight positive pressure at the output of the secondary air pump.

The vacuum is needed to control the secondary exhaust valve and this is done by a solenoid at the rear of the engine.

When the code says "insufficient air flow" is really means the O2 sensor did not switch lean enough. Since we are pumping in air into the exhaust manifold, the O2 sensor should see a lean mixture. That is how the DME checks for a working secondary air pump.

The catalytic converter can't cause this code, it has its own codes.

From here I would:
(1) Disconnect the secondary air pump hose at the exhaust manifold, start the car and see if you have air blowing. Make sure the car is COLD or the pump may not start up.

(2) Check for vacuum at the exhaust manifold valve. When the pump is on, you should have vacuum.

(3) How long have the pre-cat O2 sensors been in? Since they are the only sensor that provides feedback to the DME about the condition of the exhaust mixture, maybe they are slow to switch. If you have access to an OBD scan tool, view the output of the O2 sensor during a cold start. After about 60-90 seconds the pump will switch off, and you should see the O2 sensor react by switching to normal (or at least see it switching from less lean)

Good Luck.

[CBi]

My mechanic says at least one of the catalytic converter(s) (there supposedly are two on the car) is bad.

It's possible your mechanic may not understand how the secondary air system on your engine works.

The post-cat 02s are used to monitor the condition/efficiency of the cats themselves. That is their sole purpose - they do not provide data for monitoring of the secondary air system.

If you can hear the pump running during a cold start, and it's still throwing the codes, you may need to check the operation of/replace the vacuum solenoid that operates the valve. Sometimes the valves fail in a manner that is "invisible" to the DME.


-CBi

Indy BMW tech

[napalirick]

MaxVQ -- Sorry, I meant to say a vacuum at the output of the secondary air pump valve (going in to the secondary air pump). I realize I am supposed to have a slight positive pressure at the output of the secondary air pump.

I have checked and even replaced the electronic control valve (solenoid) at the rear of the engine that controls the vacuum to the secondary air pump valve and it appears to be working correctly because I am getting a vacuum both going into the secondary air valve and at its output -- and only when the engine is cold (off for 6-8 hours or so).

I'll try your suggestions, although the secondary air pump is in the right front wheel well on the '02 530i, which makes it difficult to access. We've had to put the car up on a lift and take off the wheel to get at it.

I believe the pre-cat O2 sensors are original equipment.

Thanks.

[MaxVQ]

I'll try your suggestions, although the secondary air pump is in the right front wheel well on the '02 530i, which makes it difficult to access. We've had to put the car up on a lift and take off the wheel to get at it.

I believe the pre-cat O2 sensors are original equipment.

To test the SAP, simply disconnect the hose at the exhaust manifold. No need to get at the SAP just yet.

As a matter of emissions and fuel economy I would change the O2 sensors ASAP. How many miles are on the car?

[napalirick]

I'll disconnect the SAP in the morning in the next day or so.

The car will hit 140K miles in the next few days. I have had little problem with it before this SES light issue.

I don't have access to an OBD scan tool. But I will change the pre-cat O2 sensors ASAP.

Thanks.

[fudman]

There is a BMW service bulletin out that identifies carbon buildup in the manifold as a cause for SAP problems but I don't think this is your problem (I'll try and post it when I get home). Given that the SAP system has new parts and appears to be functioning correctly and your pre-cat O2 sensors have 140K and are original, my guess is that the O2 sensors are the probable cause of your problem. Recommended lifecycle change is 100K for O2 sensors, so this is consistent with component failure. Recommend changing this part out out before exploring the carbon issue, which requires breaking down the engine and is much more expensive. Good luck.

[DouglasABaker]

This is pretty common on the S62, and is caused by carbon buildup in the secondary air passage of the block itself. I don't know how common it is in the M62, but if you've changed all the SA components and are still getting the code on startup, I'd guess you have CBU. On the S62 most people go with the Powerchip solution, which increases the tolerances so that the vehicle does not throw a code.

d-

[Cyrix2k]

FWIW, my car made it through emissions just by erasing the codes and driving a bit. The CEL came back on the next day

[MaxVQ]

There is a BMW service bulletin out that identifies carbon buildup in the manifold as a cause for SAP problems but I don't think this is your problem (I'll try and post it when I get home).

I think that service bulletin does not apply to the M54 as the secondary air is injected directly into the large exhaust manifold.
Other designs use small ports in the head and/or exhaust manifold.

Please post it so we know for sure.

[DouglasABaker]

FWIW, my car made it through emissions just by erasing the codes and driving a bit. The CEL came back on the next day

Congrats on living in a state that is not part of the Green State emissions program.

The OP lives in MA, which IS a Green State, and therefore will not pass if he does the same thing - his vehicle will simply register "not ready" and he'll fail.

d-

[napalirick]

That's correct. Merely turning off the SES light will not allow the car to pass emissions (the emissions computer will read that the car is "not ready"), unless the car is put through several drive cycles, which takes some time to accomplish. I guess I could turn off the SES light, drive it for a couple of hours to put it through its drive cycles (which you can pull down from the Net), and then head straight for the emission inspection station without turning off the car and letting it cool, and hope that does the trick.

However, because of the 140K mileage, I ordered the two pre-cat O2 sensors from Bavarian Auto in New Hampshire for $75 per (the local BMW dealer wanted $345 for two of them! -- that's w/o the labor to swap them out!). I'll put them in this weekend. Hopefully that will fix it once and for all.

I'll keep you posted.

[Cyrix2k]

Congrats on living in a state that is not part of the Green State emissions program.

The OP lives in MA, which IS a Green State, and therefore will not pass if he does the same thing - his vehicle will simply register "not ready" and he'll fail.

d-

Carroll County will too. You have to drive it enough to have all the self-tests pass. I reset the codes and drove ~80 miles, mostly highway, and then brought it in for emissions. Pass. If he gets the car nice and warm, resets the CEL and takes it for a spin on the highway, it should be fine.

:edit: specifically, I drove it home 66 miles, parked it in a warm garage, and brought it to the testing station the next morning.

[MaxVQ]

BMW Drive cycle guide:
http://www.europeantransmissions.com...0Procedure.pdf

It can be very difficult to get all set to ready.

[fudman]

I think that service bulletin does not apply to the M54 as the secondary air is injected directly into the large exhaust manifold.
Other designs use small ports in the head and/or exhaust manifold.

Please post it so we know for sure.

You're right. There are two TIS' covering SAP.

One does cover the M54 but that one specifies check valve replacement when soiling is found in the valve. I can't seem to attach it. The jpeg file must be too big. It's 11 05 02 (888).

This one (B 11 05 04):
http://www.bmwtis.net/tsb/bulletins/bulletin_graphic_temp/B110504g.htm
is the one that refers to engine air passage cleaning but is applicable to the S62 only.

[DouglasABaker]

Carroll County will too. You have to drive it enough to have all the self-tests pass. ...

Apparently not since you didn't complete the required drive cycles to check all the systems and set all the flags to "ready".

d-

[Cyrix2k]

Apparently not since you didn't complete the required drive cycles to check all the systems and set all the flags to "ready".

d-

My drive from college park satisfies the requirements and my OBD-II reader confirmed it. FWIW, I don't have a SAP.

[bimmerfiver]

However, because of the 140K mileage, I ordered the two pre-cat O2 sensors from Bavarian Auto in New Hampshire for $75 per (the local BMW dealer wanted $345 for two of them! -- that's w/o the labor to swap them out!). I'll put them in this weekend. Hopefully that will fix it once and for all.

I'll keep you posted.

Bavauto pre-cat O2 sensors...I wonder what brand Bavauto sold you? This is why I'd buy from EAC Tuning as you know you're going to get OEM parts. Hope all works out well for you. I plan on replacing the $2.00 gasket on my secondary air pump for no reason other than to say I did.

[DouglasABaker]

My drive from college park satisfies the requirements and my OBD-II reader confirmed it. FWIW, I don't have a SAP.

Wouldn't your lack of an SAP really kinda makes anything that your car does irrelevant in this thread?

d-

[Cyrix2k]

Wouldn't your lack of an SAP really kinda makes anything that your car does irrelevant in this thread?

d-

no, it's still emissions related. I have bad/aftermarket cats on my car. All he needs to do is get it to pass the self-test once and take it in to be tested. If he does fix it, he should still reset the codes because it needs to pass the self-test a few times before clearing the code.

BTW, I believe you can use cheap O2s made for a ford van or something to that effect. It's the same sensor as the BMW sensor but has the wrong tail.

[MaxVQ]

My drive from college park satisfies the requirements and my OBD-II reader confirmed it. FWIW, I don't have a SAP.

You removed it?
If so, did you do anything to prevent the check engine light from turning on?

[Cyrix2k]

You removed it?
If so, did you do anything to prevent the check engine light from turning on?

No, M62s never had it My early M44 doesn't have one either - from the factory. I don't know if M52 e39s had them or not - but if they didn't, I'd imagine someone could easily write some new software to delete the SAP from the 530i and not throw a code.

[napalirick]

Bavauto pre-cat O2 sensors...I wonder what brand Bavauto sold you? This is why I'd buy from EAC Tuning as you know you're going to get OEM parts. Hope all works out well for you. I plan on replacing the $2.00 gasket on my secondary air pump for no reason other than to say I did.

BavAuto sold me Bosch brand O2 sensors.