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Brake Pad Sensor Testing
 
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Pelican Technical Article:

Brake Pad Sensor Testing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$80

Talent:

***

Tools:

DVOM, jumper wires

Applicable Models:

BMW Z4 Coupe/Conv (2006-08)

Parts Required:

Brake pad sensor

Hot Tip:

Stay clear of brake dust

Performance Gain:

Proper brake pad warning light function

Complementary Modification:

Replace brake pads

BMW Z4 service brakes consist of hydraulic brake calipers and rotors, one at each wheel. When the brake pedal is pressed, brake fluid is forced out of the brake master cylinder and through the brake lines to each brake caliper. Pistons in the calipers push out and clamp brake pads against the brake rotors (or discs), thus slowing down the vehicle. A vacuum assisted brake booster multiplies the braking force exerted by the driver at the brake pedal. The parking or emergency brake is integrated into the rear brake caliper. A pair of mechanically operated cables attached to the parking brake handle actuate the parking brake lever inside the caliper.

You should check your brake pads every time you service your BMW. Replace your brake pads if thickness is 2.4 mm (0.09 in.) or below. There are brake pad wear sensors that trigger a warning light when pads reach the minimum; however the sensor is only located on one brake pad per axle, left front and right rear outer pads. This leaves three brake pads on each axle that are not monitored by the warning system. This is why periodic inspections are required. When replacing your brake pads, you can replace pads on one axle at a time. Have a new brake pad wear sensor handy. Even though the sensor may be reused, they become brittle and do not always fit tightly into new pads when reused. On BMW Z4 models, the brake pad wear sensor wiring is different than previous models; it's run in series to alert the mechanic of an issue and to inspect all the brakes. This provides the vehicle with more accurate brake pad monitoring. It is now more dedicated and prone to breaking when removed. So if the sensor shows the slightest bit of wear, replace it.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please remember to include your vehicle information.

In this article, I will show you how to check if your brake pad wear sensor is faulty.

Lift and support the axle you are replacing the brake pads on. See our tech article on jacking up your vehicle.

Remove the wheel on the axle you are checking the sensor on.

The brake pad wear sensor on the front axle is located in the left front brake caliper (red arrow).
Figure 1

The brake pad wear sensor on the front axle is located in the left front brake caliper (red arrow). The rear sensor is located in the right rear caliper. In order to inspect the sensor, you will need to remove it from the bracket. Look for wire damage, sensor wear or cranking.

On BMW Z4 models, the brake pad wear sensor wiring is different than previous models; it is run in series to alert the mechanic of an issue and to inspect all the brakes.
Figure 2

On BMW Z4 models, the brake pad wear sensor wiring is different than previous models; it is run in series to alert the mechanic of an issue and to inspect all the brakes. The reference voltage comes from the cluster and pulled to ground through the sensors. If the cluster sees the reference voltage not pulled to ground, it assumes the brake pads need inspecting. Testing this circuit is as easy as jumping out the sensors (for a quick test) but if that doesn't solve the issue, you will need to dig deeper. This diagram applies to our 2006 BMW Z4M subject vehicle. Wiring for your Z4 may vary, be sure to use a current wiring diagram for your vehicle.

The brake pad warning light (red arrow) will be on when the sensor is seen to be open, or worn out.
Figure 3

The brake pad warning light (red arrow) will be on when the sensor is seen to be open, or worn out. As soon as the circuit is closed, or a new sensor is installed, the light will go out.

Set your DVOM to Ohms.
Figure 4

Set your DVOM to Ohms. To check resistance of the sensor, measure across the sensor terminals (red arrows). Should be less than 1 ohm, as shown.

To test the front sensor voltage, set your DVOM to DC volts.
Figure 5

To test the front sensor voltage, set your DVOM to DC volts. At the front sensor, terminal 1 (blue arrow) should be reference volts (about 5 volts) as shown. Terminal 2 (red arrow) should read close to zero, as that is the ground through the rear sensor.

To test the rear sensor voltage, set your DVOM to DC volts.
Figure 6

To test the rear sensor voltage, set your DVOM to DC volts. At the rear sensor, terminal 1 (blue arrow) should be close to zero volts, ground. Terminal 2 (red arrow) should read reference volts (about 5 volts) as shown.

If you are missing the reference voltage to Pin 2 at the rear, you can simply add a ground to pin 2 at the front sensor to confirm the circuit is open.
Figure 7

If you are missing the reference voltage to Pin 2 at the rear, you can simply add a ground to pin 2 at the front sensor to confirm the circuit is open. If the light goes out, you will have to repair the harness. If you are missing a ground, you can simply add a ground at terminal 2 at the front or terminal 1 at the rear to test you theory. This diagram applies to our 2006 BMW Z4M subject vehicle. Wiring for your Z4 may vary, be sure to use a current wiring diagram for your vehicle.

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Page last updated: Sat 12/3/2016 03:08:44 AM