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Secondary air fault codes P0491, P0492 functional check low / insufficient flow.

These codes are set when secondary air system is activated and air flow is not detected. The ECM monitors oxygen sensors for lean shift during this time period. If it is not seen, low flow fault codes are set.

Secondary Air Valves
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Piping from air pump to secondary air valves can fail. Cracks develop in area where pipe meets fittings. This pipe is difficult to see due to location, under intake manifold.

Cracked Pipe
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If you have the listed fault codes and believe this to be your problem you can test it a few different ways.

1. Engine OFF. Activate secondary air pump using BMW scan tool. Listen for high pitched air leak in area of air valves or under intake manifold.
2. Engine OFF. Activate secondary air pump using jumper wires to battery positive and battery negative (use wiring diagram to identify connection points and terminals). Listen for high pitched air leak in area of air valves or under intake manifold.
3. Engine OFF. Disconnect air pipe from air pump to valves at junction located near front of right cylinder head. Using a smoke machine fill air valve side of pipe with smoke. Look for escaping smoke from pipe area under intake manifold.