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Fortunately I had my secondary air pump and valves replaced under the CPO warranty. But my CEL returned several times. Which led me to feel that carbon build up in the exhaust valve passages used by the secondary air system, like the 540 in the pic was causing the low flow.





To clear this carbon, pour Seafoam into the hose from secondary air pump to the valve and engine port before the cold engine is started in the morning.





The hose will hold just over an ounce of Seafoam. Reconnect the hose and run the car 5 seconds so the air pump blows the Seafoam into the exhaust port. Repeat this fill and restart 3 more times only running the engine 5 seconds so the secondary air pump runs for the 3 fills.

Then let the engine sit 15 minutes and warm up the car. There will be significant amounts of Seafoam carbon burnoff in the form of white smoke. The carbon burnoff will clean exhaust areas in the path to the O2 sensors that measure secondary air flow.

Since doing this using a couple of cans over a few months, the CELs have gone away and the engine feels smoother.
 

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Probably fried unless your test circuit wasn't grounded. Do step 3 of the BavAuto diagnostics to see if you get power to the pump on start up in case of fuse issues. In my case under CPO warranty, BMW replaced the secondary air pump first - but the codes didn't disappear until the Seafoam in the tubing trick.
 

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It's better to try the Seafoam treatment first because it's an easy first step. See in the above post. It may be all that is needed to clear the low flow codes. After 150K you should repeat the cleaning process several times.
 

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Funny, I have an 03' 330xi too, and I was recently told that a problem could be starting with my secondary air pump, but if so, it won't be getting worse now in the warmer weather. Said I'll have to wait until next fall/winter to see if it starts up again. Symptom was shifter/wheel/engine shaking from side to side as if an engine or transmission mount was loose.. But it goes away pretty fast after the car starts moving and the engine begins to warm up..
All that vibration could be your secondary air pump. The secondary air pump automatically shuts of in about 2 minutes. The Seafoam treatment could eliminate some of the back pressure.
 

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So do you have to do an oil change after the seafoam? Ive heard both ways and dont want to do it unless Im completely sure
You only do an immediate oil change (i.e. within 100 miles) if you add Seafoam to the crankcase. This is a way to clean the engine internals when you are planning an oil change.
When you run Seafoam through the Secondary air valve you don't need to change the oil, you will see the Seafoam and carbon deposits burn off in the white smoke.
 
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