How to test an ABS sensor with a multimeter
Content
Anti-Lock Braking System (ABS) sensors are components in modern vehicles that communicate with the ECU and monitor the amount of braking when you try to stop your vehicle.
These are sensors attached to the wheels via a wiring harness that monitor the speed at which the wheels are spinning and also use this data to determine if the wheels are locking up.
The brake applied through the ABS is also faster than the handbrake. This means they are useful in harsher conditions, such as when you are driving on wet or icy roads.
A problem with the sensor means a clear danger to your life, and an ABS or traction control indicator light requires very urgent attention.
How to diagnose the sensor for problems?
Our guide will tell you everything you need to know about how to test an ABS sensor.
Let's get started.
Tools Needed to Check the ABS Sensor
For all the tests mentioned here, you will need
- multimeter
- A set of keys
- Jack
- OBD Scan Tool
The multimeter helps us to carry out various types of sensor diagnostics and is therefore the most important tool.
How to check the ABS sensor with a multimeter
Raise the car with a car jack, disconnect the ABS sensor cable, set the multimeter to the 20K ohm range, and place the probes on the sensor terminals. You expect to get a proper reading between 800 and 2000 ohms if the ABS is in good condition.
We will delve into this testing process and also show you how to diagnose the problem by checking the readings of the AC voltage sensor.
- Jack up the car
For safety, you put the car's transmission into park mode and also activate the emergency brake so it doesn't move while you're under it.
Now, in order to have access to the sensor for convenient diagnostics on it, you also need to raise the car where the sensor is located.
Depending on your vehicle, the sensor is usually located behind one of the wheel hubs, but you can refer to your vehicle owner's manual for its exact location.
You also want to know what a particular ABS sensor looks like on your vehicle so you don't confuse the sensor with other sensors.
Place a mat under the car to keep your clothes clean while you run these tests.
- Set the multimeter to the 20 kΩ range
Set the meter to the "Ohm" position, indicated by the omega (Ω) symbol.
You will see a group of numbers in the ohm section of the meter which represents the measurement range (200, 2k, 20k, 200k, 2m and 200m).
The expected resistance of the ABS sensor requires you to place the meter in the 20 kΩ range to get the most appropriate reading.
- Disconnect the ABS cable
Now you disconnect the anti-lock brake system from the sensor cable to expose the terminals for testing.
Here you simply and neatly disconnect the wiring harnesses at their connection points and move your attention to the wiring harness from the side of the wheel.
- Place the probes on the ABS terminals
Because polarity doesn't matter when measuring ohms, you place the meter's probes on either of the sensor's terminals.
- Rate results
Now you check the meter reading. ABS sensors are expected to have a resistance of 800 ohms to 2000 ohms.
By looking at your vehicle's sensor model, you determine the correct characteristics to evaluate whether you are getting the right value or not.
Because the meter is in the 20 kΩ range, it will show a constant value between 0.8 and 2.0 if the sensor is in good condition.
A value outside this range or a fluctuating value means that the sensor is defective and needs to be replaced.
If you also get an "OL" or "1" reading, this means the sensor has a short, open, or excessive resistance in the wiring harness and you need to replace it.
ABS AC voltage test
Checking the ABS sensor voltage helps us figure out if the sensor is working properly in real use.
With the vehicle in park mode, the emergency brake applied, and the vehicle raised, perform the following steps.
- Set multimeter to 200VAC voltage range
AC voltage is represented on the multimeter as "V~" or "VAC" and usually has two ranges; 200V~ and 600V~.
Set the multimeter to 200 V~ to get the most suitable test results.
- Place the probes on the ABS terminals
Just like with the resistance test, you connect the test leads to the ABS terminals.
Luckily, the ABS terminals are not polarized, so you can simply plug wires into any of the terminals without worrying about inaccurate readings.
- Rotation wheel hub
Now, to simulate the movement of a car, you rotate the wheel hub that the ABS is connected to. This generates a voltage, and the amount of volt generated depends on the speed of the wheel.
You want to make sure you spin the wheel at a constant speed to get a constant value from the counter.
For our test, you make a revolution every two seconds. So you are not excited about the spinning of the wheel.
- Check multimeter
At this point, the multimeter is expected to display a voltage value. For our rotational speed, the corresponding AC voltage is about 0.25 V (250 millivolts).
If you're not getting a meter reading, try plugging the sensor harness into where it enters the wheel hub. If you still don't get a reading when you test your multimeter, then the ABS has failed and needs to be replaced.
A lack of voltage or an incorrect voltage value can also be caused by a problem with the wheel hub itself. To diagnose this, replace the ABS with a new sensor and run the exact voltage test again.
If you still don't get a proper voltage reading, the problem is with the wheel hub and you need to replace it.
Diagnosis with an OBD Scanner
An OBD scanner offers you an easier solution for identifying problems with your ABS sensor, although they are not as accurate as multimeter tests.
You insert a scanner into the reader slot under the dash and look for ABS related error codes.
All error codes starting with the letter "C" indicate a problem with the sensor. For example, error code C0060 indicates a problem with the left front ABS and C0070 indicates a problem with the right front ABS.
Refer to this complete list of ABS error codes and their meanings to find out what to expect.
Conclusion
The ABS sensor is a fairly simple component to test and also offers a variety of ways to diagnose problems in our vehicles.
However, with any test you wish to perform, make sure you apply the correct safety precautions and set your multimeter to the correct range to get correct results.
As mentioned in our article, remember that your safety on the road depends to a large extent on the performance of your ABS, so any defective component should be replaced immediately before the vehicle is put into operation.
F.A.Q.
How many ohms should an ABS sensor have?
A good ABS sensor is expected to hold between 800 ohms and 200 ohms resistance depending on the vehicle or sensor model. A value outside of this means a short circuit or insufficient resistance.
How do I know if my ABS sensor is bad?
A bad ABS sensor shows signs such as the ABS or traction control light on the dashboard coming on, the car taking longer to stop, or dangerous instability when braking in wet or icy conditions.
