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Secondary Air System Components Testing
 
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Pelican Technical Article:

Secondary Air System Components Testing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$200

Talent:

*****

Tools:

Set of sockets, E12, 10mm, flathead, Phillips screwdriver, plastic gasket scraper, DVOM, test light, fused jumper wires

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Secondary air valve and gasket, hose clamps, secondary air solenoid

Hot Tip:

Replace any cracked or dry rotted hoses

Performance Gain:

Repair inoperative secondary air

Complementary Modification:

Replace companion component

Secondary air injection is a vehicle emission control wherein fresh air is injected into the exhaust stream to allow for a more efficient catalytic converter. The air injection point is called the upstream injection point. When the engine is cold, air is injected upstream of the catalytic converter to clean up the extra-rich exhaust and raises the temperature of the exhaust to bring the catalytic converter to operating temperature quickly. Once the engine is warm, air injection is halted. This function usually only runs for a short time, when first starting the engine.

The secondary air system is prone to faults that illuminate the check engine light. If you have fault codes for your secondary air, check the operation of the pump. You can test the function of the secondary air components using a Mercedes-Benz scan tool. If you do not have access to one, you can check secondary air pump function when starting the engine. When a cold engine is started, the secondary air pump will run for a calculated amount of time. You can also manually test each item.

In this tech article I will go over how to test the secondary air system check valves and solenoid. The tests are going to be performed on a W211 with a 6-cylinder engine.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below.

The secondary air valves are located at the left and right corners of the engine (green arrows).
Figure 1

The secondary air valves are located at the left and right corners of the engine (green arrows). The secondary air solenoid is located at the right front of the engine (red arrow).

Working at the engine cover (red arrow), pull off the two front air duct hoses (green arrows).
Figure 2

Working at the engine cover (red arrow), pull off the two front air duct hoses (green arrows).

To detach the ducts, pull them straight off the engine cover / air filter housing.
Figure 3

To detach the ducts, pull them straight off the engine cover / air filter housing. Then pull the front of the duct out of the radiator support and remove it from the engine. Repeat this step for each duct.

Lift up and remove the front engine cover.
Figure 4

Lift up and remove the front engine cover.

Then, pull the engine cover / air filter housing straight up to remove it.
Figure 5

Then, pull the engine cover / air filter housing straight up to remove it. The cover is held on by four metal clips that grab onto rubber mounts. The front two are shown (red arrows). The rear of the cover has two as well. Once detached, remove the engine cover / air filter housing from the engine.

Secondary air pump testing: The secondary air pump is located at the front of the engine (green arrow).
Figure 6

Secondary air pump testing: The secondary air pump is located at the front of the engine (green arrow).

Secondary air pump testing: Disconnect the air pipe.
Figure 7

Secondary air pump testing: Disconnect the air pipe. Start by removing the pipe from the secondary air pump. Start the engine, (it should be cold). The air pump should run and a good amount of air should blow from the outlet the hose was just removed from.

Secondary air pump testing: Next, disconnect the secondary air pump electrical connector (blue arrow) by squeezing the release tabs and pulling it straight off.
Figure 8

Secondary air pump testing: Next, disconnect the secondary air pump electrical connector (blue arrow) by squeezing the release tabs and pulling it straight off.

Secondary air pump testing: With the connector removed, connect a DVOM across the terminals (red arrow).
Figure 9

Secondary air pump testing: With the connector removed, connect a DVOM across the terminals (red arrow). Start the engine, (it should be cold). The DVOM should display battery volts (yellow arrow). If it does and the pump did not run, the pump is faulty. If you did not have battery volts, you may have an electrical issue. Start by checking the air pump relay, it is located in the fuse and relay box in the engine compartment. Remove the relay and jump terminals 30 and 87 together, if the pump runs, replace the relay. If replacing the relay does not fix the issue, run a system test using a Mercedes-Benz scan tool.

Secondary air pump check valve solenoid testing: Start by removing the right side vacuum hose from the solenoid and connecting it to a vacuum gauge (red arrows).
Figure 10

Secondary air pump check valve solenoid testing: Start by removing the right side vacuum hose from the solenoid and connecting it to a vacuum gauge (red arrows). Start the engine. You should have manifold vacuum at all times (green arrow). If not, check if the vacuum hose is broken between the solenoid and intake manifold.

Secondary air pump check valve solenoid testing: Next, remove the vacuum hose from one of the check valves.
Figure 11

Secondary air pump check valve solenoid testing: Next, remove the vacuum hose from one of the check valves. The hose from the solenoid to the check valve (red arrows) is switched manifold vacuum. It only has vacuum when the secondary air system is activated. Start the engine, (it should be cold). The air pump should run and the vacuum gauge should read manifold vacuum (green arrow). If the air pump is running and there is no vacuum, replace the solenoid.

Secondary air pump check valve solenoid testing: Disconnect the air pipe.
Figure 12

Secondary air pump check valve solenoid testing: Disconnect the air pipe. Start by removing the pipe from the secondary air pump.

Secondary air pump check valve testing: Then disconnect the vacuum hose that runs from the solenoid to the check valves (red arrows).
Figure 13

Secondary air pump check valve testing: Then disconnect the vacuum hose that runs from the solenoid to the check valves (red arrows). Connect a hand-operated vacuum pump to the vacuum hose you removed from the solenoid. Start the engine. The valve should not leak exhaust out the hose fitting toward the air pump. There may be a slight exhaust pulse noise. Though this noise should not be loud. Pump it up to 18" of vacuum. You should hear exhaust pulses coming out of the disconnected hose (green arrow). You can also isolate each valve by only applying vacuum to a specific valve and listening for the exhaust pulses.


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