[mrboca]

You have an intermittent problem which makes the diagnosis to a particular part even more difficult. Sometimes other problems (like O2 sensors, EGR, improper coolant temperature, vacuum leaks etc.) can trigger this code, as the way it is detected is during the drive cycle the secondary air pump is turned on , air is injected into the exhaust side and the O2 sensor(s) are monitored for a very lean condition (due to injected oxygen in the air) in two consecutive drive cycles. Thus, you need to make sure there are no other conditions that would interfere with the test results (increase of lambda from the O2 sensors by 23 percent or more)

Once the problem is isolated to the secondary air injection system, then the operation of the air pump, switchover valve and the combination valves (one per bank) can be checked. The common problems are sticking switchover valve, leaky check valves (of the combi valve), air and vacuum supply hoses between components (kinks, holes , splits, loose connections), intermittent electrical contacts, and the intermittent operation of the air pump (which requires something like 35 amps, and possible to have worn brushes), and the air pump relay itself (worn contacts over time). The air pump turns on when the engine is cold for few minutes, so you can "simulate" the cold engine condition to check the air pump and the equipment down the chain.

 

[mrboca]

You should be able to check the resistance, between the terminals, no problem. From the electrical point of view, you have the battery supply in K40, relay module at the passenger side, 40 amp maxifuse (the orange big one) the air pump relay contacts and the air pump. It is just that you describe the problem as intermittent, so the continuity (low resistance) reading may or may not be there if the pump brushes are worn out. Just over the pump on the left side there is the switchover valve which is just a solenoid valve, that you may want to check the connector and operation. You should be able to hear the air pump running with engine cold for two minutes during start up.

 

[mrboca]

Please look at the attached documents. This is for W163 but the same engine / air injection system. One of the problem areas is the pump relay in K40 unit, the contacts go pitted over time and eventually stop supplying the power to the pump altogether.

 

[mrboca]

You can put your hand on the pump immediately after a cold start and you should feel the vibration of the working pump. Or you could check the air pump air output for 90 seconds or so the pump runs.

If you want the check the air pump operation with a warm engine, to turn the air pump on, you could use a little "trick" by removing the engine coolant sensor connector, and terminate the connector at the ECM end with a 2000 ohm resistor. The ECM will think the coolant is at 30 degrees C, so it will start the pump even though the engine is warm. This is just for testing purposes.

When you remove the check valves and had a look inside the holes at the engine side have you noticed any carbon / gunk buildup ? With both check valves removed when you start the engine you should have some exhaust gasses coming out from those openings to confirm that there are no blockages.

If you have a scanner with live data display (like graphs) you should be able to display the sharp change in the outputs of the O2 sensors when the secondary air injection pump runs. This is what the ECM observes to test the proper operation of the system.

It is hard to determine the condition of the air pump unless you open it up and check the condition of the components. Another failure mode of the pump is due to exhaust gasses entering in it due to defective check valves. When you open it you should be able to see the gunk inside.

 

[mrboca]

I suggest you activate the air pump and observe its air output. You can measure the resistance but with the low voltage and current of the ohmmeter, it is likely to be a not reliable measurement at static conditions (due to some electronics inside for start up.). The pump takes around 30 to 35 amps when it runs, so the running impedance is less than 1/2 ohm.

The pump runs few minutes per day (only when the engine is cold), so if the pump pumps air when it runs, I would look at other areas like the switchover valve, combi valves and clogged air passages from the combi valves to the exhaust.

 

[mrboca]

The relays are lined up like k1 k3 k2 and the relay for the air injection pump is k3,

The ECM will activate the relay during start up for around 90 seconds to 2 minutes if the coolant temperature is below certain levels (40 degrees C I think). It will also test the the operation of the system under certain condition, once per drive cycle and it turns it on few seconds or so. This is what generates P0410, not the the start up operation. There is no sensor that I know of directly controls the operation. however the ECM uses the coolant sensor data and other sensor data (like the rpms, throttle etc) to determine when to do the test. If this error condition occurs in two consecutive drive cycles, you get the CEL.