How to troubleshoot ABS wheel sensors.
This tutorial assumes you have already checked ABS codes and found a wheel sensor code. If you have not checked for ABS codes you should do so before continuing with this tutorial. Instructions can be found here: How To Check ABS Codes
Once you have determined that you have a wheel sensor code stored in the EBCM don't assume you have narrowed it down to a specific wheel. It is commonly known that the codes do not always indicate the specific sensor that is bad.
Troubleshooting Buick Reatta ABS wheel sensors is done in three basic steps to ensure they are in good working order.- Checking to see if resistance of the sensor and leads are within specifications.
- Checking to see if output voltage of the sensor is within specifications.
- Visually inspecting the sensor leads for cracks and missing insulation.
This tutorial will lead you through the logical process of troubleshooting the ABS sensors and leads to help you determine which ones need to be replaced.
ABOUT CLEARING ABS CODES: ABS codes are stored in non-volatile memory. You cannot clear the codes by unplugging the ECBM, disconnecting the battery cables or turning off the ignition switch. To clear the ABS codes you must drive the car over 18 miles per hour and they will automatically be cleared if you have repaired all problems that caused the ABS trouble codes to set. If you drive the car greater than 18 miles per hour and the yellow ABS light comes on the ECBM is still detecting a problem and codes will be present when you check the codes again.
The ECBM will not allow the codes to be cleared unless ALL codes have been read.
1. Connector Locations
The connectors can be hard to find if you aren't familiar with their locations. The photos below will give you a general idea where to look for them.
The connector for the left front wheel may be tucked below the plastic wire raceway and be hard to find.
The connector for the right front sensor may be tucked behind the coolant reservoir tank.
Look for the exhaust pipe hanger and you will see the connector against the frame rail.
Look for the exhaust pipe hanger and you will see the connector against the frame rail.
2. Electrical Tests
I recommend starting with the front wheel sensors even if your code indicates a problem with a rear sensor. Front sensors take more abuse as they turn and twist much more than the rear and they are the most likely to be defective.
Before you can test the sensor you will need to disconnect the lead from the body wiring harness. To do that you must grasp the flats on the sensor connector and squeeze to disconnect the locking tabs. While squeezing the flats on the connector work the connectors apart.
Test for proper resistance:
Once you have the lead disconnected you are ready to perform the electrical tests to determine if the sensor is defective.
- Set you multimeter to read resistance (OHMS).
- Inset the probes into the connector as show in the photo below.
(If you have an auto-ranging multimeter it may read in k ohms. 1.115 k ohm=1115ohms)
- The multimeter should read a resistance in the range of 800-1400 ohms. A reading of about 1100 ohms is most common.
Any reading on the high or low end of the range warrants closer scrutiny more testing to find out for sure if it is defective.
- Test for proper voltage:
Set your meter to read voltage of less than one volt.
- Jack the car up and secure with jack stands and release the brakes and set the transmission so the wheels will spin freely..
- Spin the wheel quickly by hand and observe the voltage reading on your meter.
The voltage should register and increase as you spin the wheel faster until it peaks out about 450 mv or .45 volt. This is the signal that the EBCM is looking at while you are driving. However, it is more interested in the frequency of this signal than its voltage level.
Repeat the tests above until you are satisfied you have obtained accurate results from your tests.
3. Test Sensor Function
Check the sensor for function after measuring the resistance. The sensor is magnetic. It should react to a metal object passing near it.
With your ohmmeter attached to the connector end - move a screw driver (or other metal object) over and near the sensor end without touching it. You will see a notable change in the reading on the ohmmeter as the screwdriver is passed over the sensor. The ohmmeter should change resistance by about 10-20 ohms. Anything less than that should be considered marginal operation and the sensor should be suspect. Go back to tab #2 and verify the resistance readings are in range. Testing the insulation in step #4 may reveal bad insulation on the leads which might be the cause of the sensor not reacting correctly.
Special thanks to Jim Finn for providing this information.
4. Inspect Sensor Leads
Do a visual inspection of the wheel sensor leads. Look closely for cracks in the insulation that will allow moisture to penetrate into the wiring. Even a small amount of moisture will cause the sensor to give a bad reading.
Here is what you are looking for:
A few small crack in the insulation might be repairable with liquid tape of something similar. Large cracks or missing pieces of insulation requires the sensor leads to be replaced or refurbished.
Thanks to members of the Reatta forums for this information. Special thanks to Michiner 55 for supplying the photos.
