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Audi A4 ABS Control Module Replacement
 

Pelican Technical Article:

Audi A4 ABS Control Module Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$1100

Talent:

**

Tools:

13mm, 11mm flared wrench

Applicable Models:

Audi A4 (2002-05)
Audi A4 Cabriolet (2003-06)

Parts Required:

New ABS control module

Hot Tip:

Clean the contacts

Performance Gain:

Better braking

Complementary Modification:

Bleed the brakes

Without a doubt, your brakes are the most important system on the car. There is an ABS control module that reads the information from various sensors on the vehicle and controls brake modulation. If this control module goes bad it can cause all kinds of problems with your braking system.

Cleanliness is very important when working on your brake system. Dirt and debris should never be allowed to get into the system or fluid. Any impurities, including water, need to be completely flushed and bled from the system. Brake fluid is hydroscopic and will naturally absorb water; if you are replacing the ABS control unit now would be a very good time to give the system a good flush, as you are going to have to bleed it before driving. If you replace the ABS system it will require coding and setting with a scan tool after installation. Also again, you cannot drive the car until you have completely bled the brake system. Please see our article on brake bleeding for additional assistance.

Replacing the ABS control module is easy, which is nice, because it is very expensive. This is also a very good time to check the entire brake system including lines, calipers, rotors and pads.

Begin by disconnecting the ground strap from the battery and placing it in an area where it will not come in contact with the post while working.

The ABS control unit (green arrow) is located between the windshield washer reservoir (yellow arrow) and the coolant overflow reservoir (red arrow).
Figure 1

The ABS control unit (green arrow) is located between the windshield washer reservoir (yellow arrow) and the coolant overflow reservoir (red arrow). While you might be able to remove the unit without removing these two components, I recommend removing them. You are going to be working around brake fluid, so you want to be able to clean the area well and space it tight with the reservoirs in place. Please see our articles on coolant and windshield reservoir removal for additional assistance.

With the reservoirs out of the way, you can get access to the two wiring connections on the ABS unit (red arrows).
Figure 2

With the reservoirs out of the way, you can get access to the two wiring connections on the ABS unit (red arrows).

The main wiring harness is on the left side of the unit.
Figure 3

The main wiring harness is on the left side of the unit. Lift up and push the hinge on the top of the harness back towards the rear of the car (red arrow).

Moving the hinge all the way back will separate the connection.
Figure 4

Moving the hinge all the way back will separate the connection. Lift it up and away from the unit. The end of the harness (red arrow) and the receptacle (yellow arrow) must be kept clean and free of brake fluid.

Disconnect the wiring connection (red arrow) from the sensor on the unit (yellow arrow).
Figure 5

Disconnect the wiring connection (red arrow) from the sensor on the unit (yellow arrow).

You do not need to remove the cowl cover (red arrow) to drain the fluid from the brake reservoir, but now would be a good time to inspect the whole braking system including the reservoir, master cylinder, lines and booster.
Figure 6

You do not need to remove the cowl cover (red arrow) to drain the fluid from the brake reservoir, but now would be a good time to inspect the whole braking system including the reservoir, master cylinder, lines and booster.

You'll want to try and get as much brake fluid as you can out of the fluid reservoir (red arrow) on top of the master cylinder.
Figure 7

You'll want to try and get as much brake fluid as you can out of the fluid reservoir (red arrow) on top of the master cylinder. Clean around the car and then remove it. Using a fluid pump or turkey baster, get as much of the old fluid out as you can. This helps prevent excessive spilling of brake fluid inside the engine compartment. It's also helpful to stuff a bunch of old rags or paper towels under the master cylinder and ABS unit to absorb any spills.

There are two plastic clips (red arrow) holding the ABS unit in its mount (yellow arrow).
Figure 8

There are two plastic clips (red arrow) holding the ABS unit in its mount (yellow arrow). Remove the clip from both the front and back of the unit; this will allow the unit to be pulled up and out from the mount.

Clean the top of the ABS unit and use a 13mm flared wrench to remove the two supply lines (red arrows) from the master cylinder.
Figure 9

Clean the top of the ABS unit and use a 13mm flared wrench to remove the two supply lines (red arrows) from the master cylinder. The lines out the top of the brakes are removed using an 11mm flared nut wrench.

Make sure to cap the lines and unit to keep anything from getting in them (red arrow).
Figure 10

Make sure to cap the lines and unit to keep anything from getting in them (red arrow).

Carefully remove the module from the vehicle taking care to clear the mount without damaging the lines and take the unit to your work bench.
Figure 11

Carefully remove the module from the vehicle taking care to clear the mount without damaging the lines and take the unit to your work bench. Use a T25 Torx to remove the two screws that hold the hydraulic unit to the module (red arrows). These screws are single use only and should always be replaced.

You can now separate the hydraulic unit from the control module.
Figure 12

You can now separate the hydraulic unit from the control module. If you are covering the hydraulic unit make sure to cover it with plastic and not cloth or a rag. Fibers from a rag can affect performance of the unit. Installation is the reverse of removal. Make sure to clean up the area under and around the ABS module of any spilt brake fluid (red arrow) before beginning reinstallation. You will need to have the unit recoded and completely bleed the braking system before driving the vehicle.



Comments and Suggestions:
Cambo Comments: I replace the left front sensor because my abs took said it’s bad and now the light is back on and the car is hard to shift gears . I would have to force it into gears . And it vibrates a lot to. When the abs light comes on it’s harder to shift gears but when it’s off it’s less hard to shift but still need force to put in gears . What you think is the problem? I ha e a 2004 Audi A4 3.0 awd v6
December 1, 2017
  Followup from the Pelican Staff: I would start by checking the vehicle for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
Guy Comments: Do these instructions apply to a 2005 S4 Cabriolet, too?
October 3, 2017
  Followup from the Pelican Staff: Yes, they should be similar. - Nick at Pelican Parts  
bawdy Comments: Please some one can help me? My 2005 A4 ABS light turns on and the speedometer wont work.. what I do is turn the car off and pump the break pedal then the turn on the car so the abs light turns off but after driving a moment the break pedal shakes and abs light turns on again. The thing is that the car does not run good once.the abs light is on... any ideas please!
August 20, 2017
  Followup from the Pelican Staff: Possibly a failing sensor. I would start by checking the vehicle for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
Audi_Man Comments: I have my ABS and ESP lights ON with code as Left wheel speed sensor open/short. I checked the sensor's resistance and its 1.7 KOhm. I now suspect its the ABS controller that is bad. Do I really need to recode the ABS controller and bleed the system if I am removing it just to check the connections in it?
June 2, 2017
  Followup from the Pelican Staff: Resistance is not a good test. You have to test the signal to the module to be sure. - Nick at Pelican Parts  
dash Comments: Abs and disc lights appears on dashAudi a4 2003 i always switch off and on engine while the car is above 60km/h. And only then it could switch off those lights.what would be a problem?
June 17, 2016
  Followup from the Pelican Staff: Could be a faulty sensor or ABS module. I would check the vehicle for fault codes to see what part is turning the lights on. - Nick at Pelican Parts  
BUZZ Comments: Its the recoding that's the issue. Where can I get this done other than the dealer who told me they would not do unless they actually replaced the module.
November 5, 2015
  Followup from the Pelican Staff: Try a local independent Audi sop. Use google or a phone book to find one. - Nick at Pelican Parts  

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Page last updated: Wed 12/13/2017 02:49:09 AM