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Control Module Replacement
 
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Pelican Technical Article:

Control Module Replacement

Tom Morr

Time:

1.5 Hours

Tab:

$927

Talent:

**

Tools:

T27 Torx bit, ratchet, extensions, knuckle joints, Phillips screwdriver, 10mm wrench

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

New or used but functional ABS, ASR module

Hot Tip:

Have a retrieval magnet handy

Performance Gain:

Restores proper functionality to ABS and ASR (acceleration slip regulation).

Complementary Modification:

Bleed the brakes

Repair procedures for the ABS controller and pump are covered in a separate article; this one focuses on the brains of the operation, the ABS control module. If you need help with your ABS controller or pump please see our articles on the controller and pump.

Because speed signals are shared between braking and traction control systems, Mercedes-Benz combines their control in a combination ABS/ASR (acceleration slip regulation) module.

Diagnosing a module malfunction is sometimes possible with an OBD-II scanner. The trouble codes will often reveal the cause(s) of the warning light(s). Wheel-speed sensors are a common culprit. In best-case scenarios, the problem is solved by cleaning or replacing the sensors and ABS sensor rings.

The brake-pedal switch is another possible cause (please see our article on replacing your brake pedal switch).

If the error codes necessitate the replacement of the module, replacement is more time-consuming than difficult. The job requires unplugging many harnesses in the control-module box -- just inboard of the battery. To access the two Torx screws that mount the module in the box, the surrounding harnesses must be unplugged.

The plugs on the battery side of the ABS/ASR module overlap and must be removed in sequence from front (bumper side) to rear (firewall side). Also, the ABS and ASR plugs have slide-lock retainers. These features make the job more time-consuming than more-familiar pull-and-poke plugs.

The retaining screws are T27 Torx. A 1/4-inch-drive ratchet and bit will work on the forward bolt. The rear screw is tucked under the cowl and requires a wobble joint, socket adapter and ratchet-wrench or possibly a thumb-ratchet tool.

Patience helpful when re-installing the module. The rear screw can be difficult to align with the mounting hole. The module's housing is metal, but the mounting bracket is plastic. Depending on your patience level, a proper-diameter self-tapping screw might save some time and frustration.

Installation is the reverse of the removal.

An ABS warning light that stays on indicates a malfunction in the system.
Figure 1

An ABS warning light that stays on indicates a malfunction in the system. Diagnostic trouble codes can narrow down the causes.

Disconnect the battery's negative cable.
Figure 2

Disconnect the battery's negative cable.

The control module box's lid is held on by four Phillips screws (green arrows).
Figure 3

The control module box's lid is held on by four Phillips screws (green arrows). Also, the battery cable must be lifted out of the mounting channel on the lid.

The ABS/ASR module is inboard, mounted parallel to the battery.
Figure 4

The ABS/ASR module is inboard, mounted parallel to the battery. It has harnesses for the ABS and ASR.

The K40 relay unit is held in place with a brass clip (green arrow).
Figure 5

The K40 relay unit is held in place with a brass clip (green arrow). Unplugging it helps clear access to the front ABS/ASR modules mounting screw.

You might be able to get at the module's screws without unplugging all the harnesses, but you will likely need all the room they can get.
Figure 6

You might be able to get at the module's screws without unplugging all the harnesses, but you will likely need all the room they can get. Each plug is different, so reconnecting them is straightforward.

The module's two main plugs are secured by sliding channels.
Figure 7

The module's two main plugs are secured by sliding channels. Unplug the harnesses and move them out of the way. The center plug is retained by the U-shaped clip take care when removing.

The module's fore mounting screw is accessible once the K40 relay unit and various wiring harnesses moved.
Figure 8

The module's fore mounting screw is accessible once the K40 relay unit and various wiring harnesses moved. We used a T27 bit on a 1/4-inch-drive ratchet.

The rear mounting screw is under the cowl.
Figure 9

The rear mounting screw is under the cowl. We slid two more harnesses off their mounts to get to the screw (green arrows).

The lever-locked plugs in the foreground overlap each other.
Figure 10

The lever-locked plugs in the foreground overlap each other. They must be removed in sequences from front to rear.

We eventually got the rear screw out using a universal joint and extension.
Figure 11

We eventually got the rear screw out using a universal joint and extension. A retrieval magnet is handy for fishing the dropped bit out of the control module box.

We found it easier to undo the rear plug once the module was free of its mounts.
Figure 12

We found it easier to undo the rear plug once the module was free of its mounts.

Once the battery is disconnected with a 10mm socket or wrench, a Phillips screwdriver and T27 bit are required for the rest of the job.
Figure 13

Once the battery is disconnected with a 10mm socket or wrench, a Phillips screwdriver and T27 bit are required for the rest of the job. The rear retaining screw can be challenging. We used a universal joint and extension for the 1/4-inch-drive ratchet.

Some owners attempt to repair their modules.
Figure 14

Some owners attempt to repair their modules. We didn't unscrew the circuit board to look for solder failures on the backside.

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Comments and Suggestions:
shelbybaddog Comments: I think I have a bad esp module on my pump. If I replace it with a new or used one is it plug and play or do I have to go to the steeler to have it programed in some way. I have a 2003 SLK 230 part number on the module is A1705450132. Thank you in advance for your knowledge.Ralph
April 25, 2015
  Followup from the Pelican Staff: The new module will need to be programmed. - Nick at Pelican Parts  

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