Logical Approach - Diagnosing BMW Secondary Air Injection

[TotalMINIBMW]

When working on BMW vehicles, you may encounter FC's for secondary air injection, quantity or individual bank problems. If you don't have ability to activate the secondary air pump, you still can diagnose the vehicle.

Hook up your scan tool and get to the status screen with the live data stream and select the parameters for both of the O2 sensors or better yet if you can see the Lambda(later cars with a wideband O2 sensor). With the car cold( so the pump will be activated by the ECM), start the car and listen for the pump to be on. If the pump is on, look at your O2 or Lambda.......keep watching it until the pump automatically turns off. O2 or Lambda will go high(indicating lean) with the pump on and will fall dramatically with the pump shut off. If your pump runs and the 02 or Lambda doesn't change, you'll need to know how the system operates.

Some systems simply use a diverter valve with a vacuum actuated solenoid to open the valve and let the air into the exhaust stream. In that case you'll need to check for a steady vacuum with the pump activated and ECM trying to "work" the secondary air injection system. No vacuum, look for split hoses along the valve cover on 6cyl or just follow the vacuum line on any model. The Vacuum solenoids are usually pretty trouble free. On models with a non-return valve the task is much simpler, no vacuum to open any valves, it just uses the pressure from the pump to open the valve. Check the output of your pump. They output alot of air....like a vacuum that has the hose reversed for blowing. If the pump outputs plenty of air, you probably have a stuck non return valve or a clogged exhaust port on an earlier V-8.

It's even easier to diagnose on a V-8 or a split bank motor. Rarely is there a problem with both non-return valves at one time. Look for Lambda or the O2 to change on one and not the other. O2 or Lambda going lean on any bank indicates a working pump, but if only one changes then you know that one valve is stuck.

HTH, Chad