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Pelican Technical Article:

ECU Removal

Steve Vernon

Time:

30 minutes30 mins

Tab:

$0

Talent:

*

Tools:

Hands

Applicable Models:

Mercedes-Benz C350 (2008-15)
Mercedes-Benz GLK350 (2010-15)

Hot Tip:

Wiggle and pull at the same time

Performance Gain:

Trouble shooting ECU

Complementary Modification:

Change cabin air filter

If you are replacing the ECU unit on your Mercedes W204, make sure to read, store and transfer the stored data from the old ECU to the new unit using a STAR diagnosis tool. If you are just removing the unit while working on the motor it is still a good idea to read all of the codes and fault memories before removal. Removal is simple and easy and needs no tools other than your hands.

The ECU or engine control unit is located right on the top of the engine and can be seen in the cut out of the engine covers (red arrow).
Figure 1

The ECU or engine control unit is located right on the top of the engine and can be seen in the cut out of the engine covers (red arrow). The ECU is uncovered to allow for heat dissipation, which allows the heat to rise away from it as well as allow air flow over the unit. To remove the unit you must first remove the engine covers. Please see our article on engine cover removal for additional assistance.

Before removing make sure that the ignition switch is off and has been for at least five minutes.
Figure 2

Before removing make sure that the ignition switch is off and has been for at least five minutes. While Mercedes does not state that you need to disconnect the battery when removing the unit I like too. Please see our article on battery connectivity with help disconnecting the ground on the battery (yellow arrow) if you choose to disconnect the battery.

With the engine covers off you can see the ECU unit sitting on four rubber and plastic mounts (yellow arrows) There are two wiring harnesses connected at the rear (red arrows).
Figure 3

With the engine covers off you can see the ECU unit sitting on four rubber and plastic mounts (yellow arrows) There are two wiring harnesses connected at the rear (red arrows).

The wiring harnesses are connected by shift interlock connections.
Figure 4

The wiring harnesses are connected by shift interlock connections. Begin by pulling the lock connection out towards the fender (red arrow). This will slide the harness back off the unit.

It is a tight fit behind the ECU with the other wiring harnesses so use care and completely separate the harness form the unit (red arrow), making sure you do not damage the small pins and connections.
Figure 5

It is a tight fit behind the ECU with the other wiring harnesses so use care and completely separate the harness form the unit (red arrow), making sure you do not damage the small pins and connections.

Remove the other wiring harness in the same fashion (red arrow).
Figure 6

Remove the other wiring harness in the same fashion (red arrow).

With the wiring disconnected the ECU is sitting on four plastic mounts inside rubber isolators (red arrows).
Figure 7

With the wiring disconnected the ECU is sitting on four plastic mounts inside rubber isolators (red arrows).

Gently wiggle and pull the unit straight up and out.
Figure 8

Gently wiggle and pull the unit straight up and out.

Check the four plastic mounts for cracks or other damage and replace them as needed.
Figure 9

Check the four plastic mounts for cracks or other damage and replace them as needed.

If the rubber isolators have seen better days you can replace the two mounts (red arrows).
Figure 10

If the rubber isolators have seen better days you can replace the two mounts (red arrows). Installation is the reverse of removal.






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Page last updated: Fri 8/18/2017 03:05:11 AM