If you’re experiencing an ABS issue where the brake pedal causes the ABS to pulsate or activate even when the vehicle is idle, the likely culprit is a failed ABS module relay.

The good news is that these relays are straightforward to replace.

There are three relays that control the entire ABS system:

1. An ABS overvoltage relay located under the driver’s knee bolster (on early cars).
2. Two relays mounted directly on the ABS module.

Early Models (Pre-1988)

Pre-1988 cars feature an overvoltage relay (BMW PN: 34521154894 or 34520005192) located under the driver’s knee bolster near the ABS module. These relays often fail due to a thin wire fuse. In an emergency, it’s possible to resolder the fuse. However, note that a soldered fuse will no longer trip at the same amperage in the future. Alternatively, you can replace it with a KAE 3.904.100 relay.

Accessing the Other Two Relays

The two remaining relays are housed within the ABS module itself. To access them, remove the single screw securing the module’s cover.

Relay Differences: Early vs. Late Models

Early and late E30 models use different relay part numbers because of design variations:

• Early models: These use ABS pumps controlling three valves (front left, front right, and rear together). Typical relays for early cars include:
  • Bosch 0332002176 (BMW PN: 34511179403)
  • Bosch 0332205003 (BMW PN: 34511154919)
• Later models: These feature ABS pumps with four valves, controlling all four corners independently. Refer to the part numbers for later E30 models in the table below:

Also reference this article on how to quickly test your ABS wheel speed sensors:

E30 testing all ABS speed sensors the easy way

This entry was posted on January 10, 2025 at 10:03 pm and is filed under Do it Yourself. You can follow any responses to this entry through the RSS 2.0 feed.