This is to test the front right ABS sensor on my 2010 Lexus IS250, 2nd gen, rear wheel drive (RWD), manual transmission.
The following can be used on the other side as well. *This is an active sensor (not a passive one) and requires vehicle power to test*

Step 1: Jack car and remove tire.

Step 2: Turn steering wheel all the way right.




Step 3: Remove sensor connection - Insert a smallish flat head screwdriver under tab and pull straight back




Here's a better pic of the harness



Step 4: Test voltage coming to sensor: You must turn the car on to get power to the sensor:

1. Using a multi-meter
   1. Set meter to 20 volts DC
   2. Insert probes into harness
   3. It should read roughly +13.5 volts
   4. If you have voltage, the signal is getting to sensor. Go to Step 5 to test sensor.
   5. If you do not have voltage you will have to test the wiring up to the fuse box. You can test the connection behind the liners using the same steps as above. See Pic 6.
2. Using an LED: (you need a resistor otherwise the LED will blow)
   1. Create a test lead using wires, 330 ohm resistor (orange, orange, brown), and a RED led (low power, basic led - not the super bright ones) and a breadboard (optional - but easier)
   2. Connect above in this order: Red wire (positive) --> resistor --> LED positive (longer) end --> LED negative --> Black wire (negative). Here’s how I did it:
      
   3. Insert positive and negative wires into harness
   4. If light comes on, the signal is getting to sensor
   5. If you have no light, reverse the positive and negative leads. The test light is polarity specific.
   6. If you do not have voltage you will have to test the wiring up to the fuse box. You can test the connection behind the liners using the same steps as above. See Pic 6. PIC 6 - To access the harness remove the bolts of the front liner - there are also a few underneath the car towards the front

Step 5: Testing the sensor
*THIS IS NOT DIAGNOSTIC NOR IS IT DEFINITIVE*
To test this sensor you need to take the LED tester from above and insert it into the ABS circuit. It is easier to do this at the harness connection behind the liner (Pic 6) but it can be done at the connection at the wheel.

1. Strip the ends of the positive and negative test leads to expose a good inch (4cm) of bare wire.
2. Insert one wire into one of the connections in the harness. With a small flat head screwdriver, push the wire down into the housing as far as you can go. Then bend the wire around the outside of the housing and hold with your finger or tape. Do the same with the other wire/connection: This shows the basic idea:
3. 
   If you do not push the wires to make a loop in the housing they will be pulled out of the connections when you plug into the sensor.
4. Plug into sensor
5. Turn car on
6. If the led is on, continue. If is is not, reverse the positive and negative wires in the test circuit. If you still have no lit LED, retry inserting the test led wires.
7. Turn the hub slowly
   1. If the LED flickers the sensor is working - something to do with a square wave that's being sent to the computer
   2. If the LED does not flicker - your sensor may be broken

NOTES:
- I found the following OBD2 code's testing the ABS system:

• C1241 - Low or high power supply voltage
• C1401 - Malfunction in front speed sensor RH circuit

- When I did my testing I started on the sensor that was working so I would know what to look for in all the voltage values and the flickering of the LED
- I cleaned the connection terminals in the harness (at the wheel and behind the front liner) with WD40 and took the sensor out to inspect it and the bearing. When I put it all back together, the OBD2 code did not reappear on the code reader. So I don't know what exactly fixed my issue.
- I will to a "how to" to replace the sensor and leave a link How To Remove Front ABS Sensor Lexus IS250 if people would like to know how.

Lastly:
This is my contribution to this wonderful forum. I have used this site to do so many things to my car. Thank you all for helping each other.

 

Thank you!!!