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N54 Engine Catalytic Converter Replacement
 
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Pelican Technical Article:

N54 Engine Catalytic Converter Replacement

Nick Czerula

Time:

6 hours6 hrs

Tab:

$1200

Talent:

*****

Tools:

Set of sockets (8mm, 10mm, 12mm, 13mm, E10), pipe cutter, flathead screwdriver, pry bar

Applicable Models:

BMW 535i/xi Sedan (2008-10)
BMW 535xi Wagon (2008)

Parts Required:

Catalytic converter, gaskets, exhaust clamps, hardware and gaskets for full exhaust

Hot Tip:

Work with a cool exhaust

Performance Gain:

Replace faulty catalytic converter

Complementary Modification:

Replace in pairs

The catalytic converter's job is to clean up the exhaust leaving the engine to meet emission standards. In a catalytic converter (cat for short) exhaust gases are forced to pass through a fine-meshed ceramic matrix impregnated with platinum-iridium alloy. These metals bring unburned CO and hydrocarbon molecules together with excess oxygen in the exhaust and accelerate oxidation. This chemical reaction creates heat and the heat further improves oxidation efficiency; therefore cats need to run at a high temperature for maximum efficiency. Over time the high heat as well as contaminants in the exhaust melt or otherwise damage the ceramic matrix in the cat so that it requires replacement.

BMW E60 models with an N54 (turbocharged) engine utilize two catalytic converters, one mounted to the outlet of each turbocharger. Catalytic converter replacement is a big job and requires removing the complete exhaust system and many other components. Read through the procedure thoroughly before beginning. Plan for this job to take a day, if all goes as planned.

A damaged catalytic converter can rarely be diagnosed visually. Cat failure usually sets fault codes in the ECM. Before you remove the exhaust system, use a BMW scan tool or equivalent to download fault codes and determine if there is any reason to suspect the failure of these major emissions control components or of the oxygen sensors. The oxygen sensors, particularly those downstream of the cats, may be easier to remove once the exhaust system is off the car.

The most common fault codes that show your catalytic converters are faulty include: P0420 Catalyst System Efficiency Below Threshold (Bank 1) or P0430 Catalyst System Efficiency Below Threshold (Bank 2). Bank 1 refers to the catalyst attached to the front three cylinders (1-3). Bank 2 refers to the cat attached to the rear three cylinders (4-6).

You do not have to replace both cats at the same time. Replacing only the faulty one can save quite a bit of money. However, keep in mind, if one is faulty the other may not be far behind. When dealing with the previously mentioned fault codes, check that the engine is running well and there are no other fault codes stored before condemning the cats.

When removing the exhaust system, have new fasteners, gaskets and rubber insulators on hand to help complete the repair.

When removing the exhaust system and particularly if you are going to store it while other repairs are taking place, be sure to protect the oxygen sensors and their electrical leads. Do not drag the exhaust system on the ground carelessly.

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 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. 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. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Raise and support the rear of the vehicle on jack stands. See our tech article on jacking your vehicle. Wear those safety glasses whenever you work under your automobile.

Remove the engine and transmission splash shields and reinforcement plate. See our tech article on engine splash shield and reinforcement plate removing.

Working at the bottom of the transmission bell housing, remove the oxygen sensor electrical connectors from the holders (red arrows).
Figure 1

Working at the bottom of the transmission bell housing, remove the oxygen sensor electrical connectors from the holders (red arrows). Mark the electrical connectors so they are not mixed up later. Then pull the electrical connectors apart to disconnect them (inset). Once disconnected, remove the wiring harnesses from the mounts (blue arrows). The mounts are spring loaded. Open them while pulling the harnesses out.

Working above the front exhaust pipe, remove the 10mm sheet metal nut (red arrow).
Figure 2

Working above the front exhaust pipe, remove the 10mm sheet metal nut (red arrow). Then remove the 8mm fastener (blue arrows).

Remove the front pipe exhaust heat shield from the vehicle.
Figure 3

Remove the front pipe exhaust heat shield from the vehicle. Slide it out toward the front of the vehicle to remove it.

Working below the catalytic converters, remove the two 10mm heat shield (blue arrow) fasteners (red arrows).
Figure 4

Working below the catalytic converters, remove the two 10mm heat shield (blue arrow) fasteners (red arrows).

Remove the catalytic converter heat shield from the vehicle.
Figure 5

Remove the catalytic converter heat shield from the vehicle. Slide it out toward the left side of the vehicle to remove it.

Remove the complete exhaust system.
Figure 6

Remove the complete exhaust system. See our tech article on exhaust replacing. Then, working above the front exhaust flanges, remove the two 13mm support bracket nuts (red arrows). The bracket has slots (blue arrow) to help when removing, so you can leave it in place.

Working at the top-side of the engine, remove the engine covers and cabin microfilter housing.
Figure 7

Working at the top-side of the engine, remove the engine covers and cabin microfilter housing. See our tech article on engine covers removing. Then, remove the oxygen sensor electrical connectors from the holders (red arrows). Mark the electrical connectors so they are not mixed up later. Then pull the electrical connectors apart to disconnect them (inset). Once disconnected, remove the wiring harnesses from the mounts (blue arrows). Then feed the harnesses out from behind the cylinder head (green arrow), removing them from any mounts and snagged areas.

Working in the right side wheel well, remove the wheel well housing liner (red arrow).
Figure 8

Working in the right side wheel well, remove the wheel well housing liner (red arrow). See our tech article on wheel well housing liner replacing. Models with all-wheel drive (535xi), remove the right front drive axle first. See our tech article on front drive axle replacing. If you feel like you might damage the oxygen sensors at any time, remove them as well. However, I find it much easier to swap them over to the new parts once the cats are removed.

The tricky part is removing or loosening the front catalytic converter clamps.
Figure 9

The tricky part is removing or loosening the front catalytic converter clamps. Start with the rear most cat, bank 2. I use a flex-head ratchet with a 13mm socket to loosen the clamp. Once it is loosened, I can usually remove it the remainder of the way by hand. Make sure the bolt for the clamp is removed. Then lever the clamp off the cat using a flathead screwdriver. The clamp will stick a little. The inset shows what the clamp looks like.

Next, repeat the last step for the front cat clamp, bank 1.
Figure 10

Next, repeat the last step for the front cat clamp, bank 1. The bolt (red arrows) for the clamp on my subject vehicle was just behind the O2 sensor. I used a two-inch extension and a 13mm swivel socket.

With both cat clamps removed, feed the cat for bank 1 out of the engine compartment.
Figure 11

With both cat clamps removed, feed the cat for bank 1 out of the engine compartment. Work slowly and check for snagged wires. The bank 2 cat (blue arrow) is removed next.

Feed the cat for bank 2 out of the engine compartment.
Figure 12

Feed the cat for bank 2 out of the engine compartment. Work slowly and check for snagged wires. Note how the cat is removed from the support bracket (red arrow).

Once the cats are removed, be sure to label them to make reinstalling easier, if you plan to reuse one or both.
Figure 13

Once the cats are removed, be sure to label them to make reinstalling easier, if you plan to reuse one or both. Remove the old gaskets from the cats (blue arrow) and the turbochargers (red arrow). If needed, gently lever them out using a flathead screwdriver. When installing, use new gaskets, clamps and fasteners. Install the cats in the reverse order of removal. To reiterate, bank 2 goes in first. Then install bank 1. Be sure they are properly secured in the support brackets. Install the nuts finger tight until the clamps at the turbocharger are in place. Then align the exhaust, tighten the clamps. Then tighten the support bracket nuts. When you're finished with this project, you should be proud of your work. It's a time-consuming tech job.

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Page last updated: Fri 12/2/2016 02:38:59 AM