State inspection was due on the BMW last November .
One of the persistent issues we have had with the car since we bought it two years ago was a "service engine soon" light coming on every so often . When I plug in my code reader to the ECU it tells me failure codes are P0491 and P0492 " Secondary Air Injection System Insufficient Flow" .
Further digging on the internet tells me the "secondary air system" operates only on cold start , and pumps air into the exhaust manifold , for a total of ninety seconds , in order to fool the ECU into thinking it is running leaner than it actually is , precisely when it is giving it extra fuel to start . It only operates for ninety seconds when the engine temperature is below 120 deg F. Strictly a People's Republik of Kommiefornia requirement , so of course they put it on all BMW cars sold in the US . European market BMWs do not have this system and it is not critical to the proper operation of the car . I have been using my code reader to clear the malfunction code when it appears , which is only every three cold start cycles when the secondary air system fails to operate as intended .
But , since last November the State of Maine has changed its rules and inspection stations now must check that the Malfunction Indicator Light (MIL) is operating and has not been disabled in order to hide a malfunction , and all sensors must be "ready to read" with actual operating data . If you clear the codes and drive it long enough without correcting the failure the MIL reappears and you do not pass . So when I took it in having just cleared the code. . . it failed on because the ECU was "not ready to read" . . . So that leaves me no choice but to go down the dreaded rabbit hole again .
This is the general schematic of the secondary air system , simple enough in principle but clearly fraught with multiple possible failure points at every turn . Vacuum is drawn from the intake manifold via an 1/8th inch line through a non return valve , an electric vacuum valve opens when power is applied , and said vacuum then opens the air pump valve on the exhaust manifold that allows the Secondary Air Pump to feed air into the exhaust manifold .
NOTE: the electric vacuum switch as shown in the above photo is now zip-tied in an accessible location . Manufacturer location is inaccessible under the intake manifold .
I test the air pump valve with a hand held vacuum pump and confirm that it opens when ten PSI of vacuum is applied . It closes as it is supposed to, when vacuum is released . I bench test the electric vacuum valve and that operates as it should , opening when twelve volts are applied and closing when there is no voltage supplied . So we know those two components are sound and as I just replaced the vacuum hoses I know I am good there too . So what gives ?
Don't forget to scratch a mark on all parts of the layer cake as if you get to reassemble it you want it all in the same orientation .
Blow out with compressed air , lube the bearing on one end and the bushing on the other and reassemble .
Reinstall the pump in the car . . . . aaaaaaand it still don't power up when I do a cold start .
When I check the plug that feeds 12V power to the pump on cold start , I get zip . Additionally the plug that feeds the electric vacuum switch also provides no power on cold start .
WTF? what is wrong with me ?
So further down the rabbit hole we go .
Check al fuses in the drop down panel inside the glove box , as well as those in the engine bay compartment on the driver side next to the brake master cylinder , and confirm that they are all good .
But when I put it all together I still can't get the secondary air system components to play nice and operate on cold start....aghhhhhhhhhhhh
Been at this crap for four days straight now
In frustration I simply start the car and let it come to temperature for ten minutes while I clean my work bench , close shop for the night , have a beer and ponder the situation . I am yet no smarter about it all .
Next morning , just for yucks , I try starting again and miracle of miracles , I hear the air pump come on and no MIL .
OK . I am still no smarter but I can only assume that the ECU needed to find itself again with some real world operating temperatures to load all the fields I had cleared .
Drove it twenty five miles up to mom's and back so the ECU could get some more operating data and reload all its fields . Three cold starts more and the MIL has yet to reappear so I figure we are good .
Took it in next day for a re-scan at the inspection station and got my sticker .