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Secondary Air Components Testing
 
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Pelican Technical Article:

Secondary Air Components Testing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$250

Talent:

***

Tools:

Sockets 13 10 mm, flathead screwdriver, DVOM

Applicable Models:

Z4 M54 (2003-05)
Z4M S54 (2006-06)
Z4 N52 (2006-06)
M3 (N/A-A)

Parts Required:

Secondary air pump, air valve and gasket, air hose

Hot Tip:

Replace any cracked or dry rotted hoses

Performance Gain:

Working secondary air

Complementary Modification:

Replace engine air filter

The secondary air system is used to improve catalytic converter efficiency and reduce the emission of harmful combustion byproducts in automotive exhaust. For a short period after a cold start, the catalytic converter is not hot enough to efficiently combine unburned fuel with available oxygen. An electric air pump forces fresh air into the exhaust stream just before the exhaust enters the exhaust manifold. This extra air supplies the catalyst with additional oxygen, thus speeding up the combustion of unburned pollutants and raising catalyst temperature rapidly. When the catalyst reaches what is called "light-off temperature" (approximately 400-600 degrees F or 215-315 degrees C) it is capable of self-maintaining a high temperature and the high efficiency of combustion. At that point the secondary air system may be shut off.

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 BMW 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. The check valve is the most common part to fail. In this tech article I will show you how to test the secondary air pump and secondary air valve on 6-cylinder S54 engine.

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out body or interior items.

Keep in mind that when your car was serviced before, parts may have been 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 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. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

An electric air pump (red arrow) forces fresh air into the exhaust stream just before the exhaust enters the exhaust manifold (yellow arrow).
Figure 1

An electric air pump (red arrow) forces fresh air into the exhaust stream just before the exhaust enters the exhaust manifold (yellow arrow).

First, disconnect the secondary air pipe from the pump.
Figure 2

First, disconnect the secondary air pipe from the pump. Squeeze the collar (red arrows), and then pull the pipe straight off the secondary air pump to remove. With the pump hose off, start the engine. The pump should turn on and blow air for about 10 to 15 seconds. If not, check the power feed to the pump using the following steps.

To test the check valve, pull back the heat shield, then disconnect the secondary air pipe from the pump.
Figure 3

To test the check valve, pull back the heat shield, then disconnect the secondary air pipe from the pump. Squeeze the collar, and then pull the pipe straight off the secondary air valve to remove.

Start the engine, no exhaust should flow out of the valve (red arrow).
Figure 4

Start the engine, no exhaust should flow out of the valve (red arrow). If you hear or feel exhaust pulses, replace the valve and check the pump for water intrusion.

To test the pump circuit start by disconnecting the electrical connector.
Figure 5

To test the pump circuit start by disconnecting the electrical connector. Working at the bottom of the pump, disconnect electrical connector by squeezing tabs and pulling is straight off. Once off, you can test for voltage at the wires. The pump is supplied constant ground to terminal 1 (blue arrow) and switched power to terminal 2 (red arrow). Connect backprobes or test leads, then connect your DVOM to the leads.

Start the engine.
Figure 6

Start the engine. The pump should be activated for about 10: 15 seconds. The DVOM will read Battery volts (voltage the battery is at, 12 volts for example). Keep in mind, a test light may light with a low supply voltage, a DVOm is the best choice. I suggest load testing using a test light and a DVOM. Connect the DVOM across the secondary air pump electrical connector terminals and take a reading. It should read battery volts when the pump is activated or commanded on. Then connect an incandescent bulb style test light to the battery ground and touch the test light probe tip to the positive wire (red arrow) you are backprobing with the DVOM. Your reading should hold steady. A maximum drop in voltage of 0.5 volts is OK. Anything more is a problem. If you find a problem with the connector, replace the pigtail with a new one. Cut the harness back enough to find good, clean wire, then butt connect and seal the harness.

To test the pump circuit ground, keep your meter connected as it was in the previous step.
Figure 7

To test the pump circuit ground, keep your meter connected as it was in the previous step. Then connect your incandescent bulb style test light to the battery positive terminal and touch the test light probe tip to the negative wire (blue arrow) you are backprobing with the DVOM. Your reading should hold steady. Take is a step further by moving your DVOM negative test lead to battery ground, then connect the positive test lead to the ground at the pump connector. Load the circuit again using the test light. Your reading should be close to zero, then when loaded a maximum increase in voltage of 0.5 volts is OK. Anything more is a problem. You will have to repair the ground.

Remove the glove box.
Figure 8

Remove the glove box. See our tech article on glove box replacing. Then remove the two Phillips head screws for the fuse panel (red arrows).

Push the fuse panel toward the firewall as you pull it down, detach the top grommet (blue arrow) from the bore (red arrow) at the instrument panel.
Figure 9

Push the fuse panel toward the firewall as you pull it down, detach the top grommet (blue arrow) from the bore (red arrow) at the instrument panel. Be careful not to lose the rubber grommet, if you do, get a new one. You don't want a rattling fuse panel, as it could cause electrical issues. Once the fuse panel has been lowered, do not remove the two remaining Phillips head screws (purple arrows).

Pull the panel out and rotate it so the back is visible.
Figure 10

Pull the panel out and rotate it so the back is visible. Then, locate the secondary air relay (red arrow), otherwise known as K6304a.

With the relay removed, you can identify the terminals and functions.
Figure 11

With the relay removed, you can identify the terminals and functions. Terminal 30 (red arrow) is constant power to the relay from F56. This should have battery positive volts all the time. Terminal 85 (yellow arrow) is the battery negative side of the low current switch, from the DME to activate the relay. It is about 5 volts with the relay unplugged and the key on, should be close to zero volts when the pump is activated, and about battery volts when the relay is plugged in, pump off with the key on. This should be close to zero volts with the key ON. Terminal 86 (purple arrow) is the battery positive to the relay from Fuse F33. Terminal 87 (white arrow) is the battery positive output to the secondary air pump. Terminal 87a (blue arrow) is a ground. This info is from a 2006 Z4M, be sure to check the wiring for your model. Also note the terminal identification on the relay does NOT match the actual relay panel wiring. Keep this in mind when testing if something doesn't seem right.

To activate the pump manually, used a fused jumper wire and jump terminals 30 and 87 (purple arrows).
Figure 12

To activate the pump manually, used a fused jumper wire and jump terminals 30 and 87 (purple arrows). The pump should run when this is jumped. Be sure to use a fused heavy gauge jumper wire set (red arrow).

With an advanced scan tool, you can also activate individual components like the secondary air pump (red arrow).
Figure 13

With an advanced scan tool, you can also activate individual components like the secondary air pump (red arrow). Very helpful, if you have this option, which most of us do not. That is why the manual checks are always a sure thing.

Terminal 85 (red arrow) is the battery negative side of the low current switch, from the DME to activate the relay.
Figure 14

Terminal 85 (red arrow) is the battery negative side of the low current switch, from the DME to activate the relay. It is about 5 volts (white arrow) with the relay unplugged and the key on, should be close to zero volts when the pump is activated, and about battery volts when the relay is plugged in, pump off with the key on. This should be close to zero volts with the key ON.

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Page last updated: Mon 12/5/2016 03:07:02 AM