BMW E39 ABS and ASC Fault - How To Fix

[BMW]

How to Diagnose and Fix ABS Issues on an E39 BMW

If you're experiencing ABS issues on an E39 BMW, you might be facing one of the more common problems with these models. This article will guide you through identifying the specific issue, understanding which ABS module you have, and diagnosing the problem without having to remove the wheels from your car.

Step 1: Identifying the ABS Issue

First, let’s understand the issue. When you turn the ignition on, the ABS light should come on briefly and then go off. This indicates that the ABS system is functioning normally. However, in this case, the light does not behave consistently. It comes on as expected during the first ignition cycle but may fail to return after restarting the ignition. Additionally, the traction control light might be on, indicating that it’s disabled and cannot be turned on or off, suggesting a definite ABS problem.

Step 2: Understanding Your ABS Module Type

The E39 BMWs have two types of ABS modules, and it’s essential to know which one you have to proceed with the correct diagnosis:

1. Earlier Model (Pre-1997): This version’s ABS module is located inside the car, away from the engine bay, making it less prone to heat-related issues.
2. Later Model (Post-1997): This version’s ABS module is located in the engine bay, near the exhaust manifold. The module in this location is prone to issues due to heat exposure from the exhaust manifold, leading to dry solder joints within the unit.

To determine which module you have, open the engine bay and locate the ABS module. If it’s near the exhaust manifold, then you have the later model, which is more susceptible to heat-related issues.

Step 3: Locating and Accessing the ABS Module

If your module is inside the car, it’s positioned behind the glove box. Here’s how to access it:

1. Open the glove box and look underneath. You should see a beige tray that can slide out.
2. Behind this tray, you’ll find the ABS module. You don’t need to remove the entire glove box—just slide out the tray to reach the module.

If your module is in the engine bay, proceed with the diagnosis directly from there.

Step 4: Running Diagnostic Tests on the ABS Module

Whether your ABS module is located in the engine bay or behind the glove box, these tests will help identify the fault. You won’t need to remove any wheels to perform these checks.

1. Resistance Test: This test will help you check the ABS sensor's resistance. Each sensor should show similar resistance; variations might indicate a problem.
2. Voltage Test: This will ensure the correct voltage is reaching the module and sensors.
3. Diode Test: This checks the flow of current within the system and will identify any faults in the electrical pathways.
4. Earth Test: The earth test ensures that the ABS module is grounded correctly, as poor grounding can cause the system to malfunction.

These tests should provide enough information to pinpoint the issue with the ABS system without the need for extensive disassembly. If you find that the module has dry solder joints due to heat exposure, it may require professional repair or replacement to resolve the problem.

Final Notes

The steps above should help you diagnose and potentially fix common ABS issues on your E39 BMW. Remember, identifying which ABS module your car has will guide you in accessing and testing the system more efficiently. For more complex repairs, consulting with a specialist may be the best approach, especially for handling solder issues or replacing the module.