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BMW Windshield Wiper Rain Sensor Malfunction

Windshield Wipers

Many BMW vehicles are equipped with rain sensors that activate the wipers when water is detected on the windshield. These sensors are major improvements over the standard, intermittent windshield wipers, but when they do not work properly, it can be very frustrating, as well as being a significant safety hazard.

A few years after purchasing my 2000 BMW 528, the windshield wipers would occasionally stop working in the rain-sensing mode. They would operate properly for a while, but after an unspecified amount of time, when in pause mode, they would stop completely. The wipers could then be turned to the full-wipe mode, where they would begin working again. Then, if the windshield wipers were turned back to the rain-sensing mode, sometimes they would start working again, at least for a short period of time.

After experiencing this problem a few times, I took the car to the dealer for repair. Unfortunately, since the problem was sporadic, the windshield wipers did not malfunction while being checked by the dealer. So, I had to try to find a solution on my own. After a lot of troubleshooting, I was able to pinpoint the defective part and fix it, so that my windshield wipers worked as expected. If you are experiencing similar problems with your windshield wipers, this relatively quick and inexpensive solution may fix your problem.

Root Cause and Solution

The root cause of the defective windshield wipers on my car was a faulty wiper module. This module has two electromagnetic relays. The lower electromagnetic relay is the switch that turns the wipers on or off, based on the signal from the rain sensor in the windshield. Figure 1 illustrates the wiper module and shows a close-up of the degraded (blackened) relay contacts. Apparently, these degraded electrical contacts allowed the wipers to operate in the rain-sensing mode for a period of time until heat or other factors caused them to malfunction. Then after cooldown, the relay would operate properly for a while until another cooldown was necessary.

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Therefore, the wiper module had to be replaced. Although the module is a plug-in design, it can be a challenge getting to it. Nevertheless, the change-out is certainly doable for anyone with basic mechanical skills. If you decide you want someone else to make the repair, this information will save a lot of diagnostic time.

Replacing the Module

Ask your BMW dealer for the location of the wiper module in your BMW. In the 2000 BMW 528, it is located under the passenger side micro filter housing. To make sure you get the correct replacement part for your BMW, remove the module and take it to your local dealer for reference.

It would be very beneficial to take photographs of the work area during the replacement process. There are only a few parts to disassemble and then reassemble, but having these photographs will help to ensure a successful repair. The only tools you need for the 2000 BMW 528 series are pliers and a 3/16″ (5 mm) hex driver (or Allen wrench).

Do the following to remove and replace the module in the 2000 BMW 528:

1. Locate the micro filter housing on the passenger side of the vehicle. See Figure 2.

2. Remove the top cover of the housing and then the filter inside the housing. Take note of the orientation of the filter, in particular the air flow direction printed on the side.

3. Remove the lower housing of the micro filter. This can be done in the following three steps. See Figure 3.

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– Take special note of or photograph the perimeter of the lower housing attachment for reference in reassembly.

– Remove the wire clip holding the front of the housing to the top of the shock tower.

– Disconnect the duct on the right side of the housing by lifting the tabs on the clip ring and sliding off the duct.

4. Remove the lower housing by first lifting up on the right side (facing the engine) and then pulling out.

5. Next remove the plastic cover over the module bay. The four socket head screws can be removed using a 3/16″ (5mm) nut driver. See Figure 4.

6. Replace the tan-colored wiper module. Take photographs of the module orientation before it is removed, and be sure to align the bottom tabs of the replacement module in the socket in its proper position. See Figure 5.

7. Replace all the parts in reverse order.

You just fixed a nagging problem at very little cost. Plus you have the satisfaction that you solved a problem on your BMW that your dealer could not. So, good luck.