How to Diagnose and Fix ABS Warning Light

Recently I’ve got an ABS warning light on the dashboard of my car. I haven’t been driving the car for some time and rodent got inside and built a nest in the engine bay. It chewed up a few wires and caused the ABS light to come on. I was able to find and fix the problem by following a few simple troubleshooting steps. The troubleshooting methods described here will work on many different vehicles equipped with an ABS system. Let me show you how I did it!

Safety First!

Driving a car with a faulty brake or ABS system could be dangerous and can potentially cause death or injury. Please abide by all the necessary safety rules and regulations when working on your car. Car repairs can be potentially dangerous. Do it at your own risk. Refer to your vehicle owner’s manual or repair manual if you have any questions. You can also find my full Legal Disclosure page here.

Scan the ABS error codes.

When you get an ABS warning light, your vehicle’s onboard computer or ECU (Engine Control Unit) receives and interprets data from various sensors and generates an error code. You can retrieve and use that information to properly diagnose the underlying cause of the problem. To do that you will need to use a diagnostic scanner capable of reading ABS error codes. Basic entry level OBD2 scanners usually don’t have that ability and you will need to get a good scanner that is usually in a $100 price range. Alternatively, you can go to a dealer or an automotive shop and ask them to scan the codes for you. Always ask how much they charge for diagnostics. In some cases, it can be up to $100-150. This might be enough money to buy your own diagnostic scanner. Definitely, something to consider, especially if you like fixing your own cars.

I am personally using the BlueDriver scanner. It is capable of reading and clearing ABS and Brake system error codes, as well as Check Engine light, airbags, transmission, live data stream, freeze frame and more. It works through a BlueDriver app interface via BlueTooth connection and supported on both Apple and Android devices. The app also has frequently reported fixes for various error codes verified by certified ASE mechanics. The scanner supports many major car brands including  GM, Ford, Chrysler, Toyota, Lexus, Scion, Nissan, Infiniti, BMW, VW, and 2003+ Honda or Acura. You can check current prices for this scanner here.

The error code on my 2007 Nissan Altima was C1103. Below are some other similar error codes and their definitions that you may get. *Keep in mind, same error codes may have completely different definitions across various car manufactures. Be sure to refer to the code definition provided by your diagnostic scanner.

  • C1101: Rear right sensor 1
  • C1102: Rear left sensor 1
  • C1103: Front right sensor 1
  • C1104: Front left sensor 1
  • C1105: Rear right sensor 2
  • C1106: Rear left sensor 2
  • C1107: Front right sensor 2
  • C1108: Front left sensor 2

As you can see, error codes can give you a pretty good idea what to look for. In my case, there was an issue with the front right ABS sensor circuit.

Diagnostics and Repair

1. Clear ABS error codes

In order to properly diagnose the ABS issue, the diagnostic trouble codes (DTC) must be active. In some cases, past error codes are still stored in the ECU even after the problem has been fixed. This usually happens if DTC’s haven’t been cleared after performing repairs. You can try to clear the ABS error codes and then drive your car at speed greater than 20 mph (32 km/h). Scan your car for error codes again. If you cannot replicate the issue, and if there is no more DTC’s stored in the ECU, you should be all set.

2. Visually inspect ABS sensor for damage

Safely jack up the car and remove the wheel where the ABS sensor in question is located. Visually inspect the ABS sensor, wires, harness, connectors, and terminals for any signs of damage or deformation. Replace or repair any damaged components if necessary. Also, check if the sensor is displaced because of the rust or suspension components damage.

3. Check ABS actuator & control unit connectors

Unplug and inspect the ABS actuator & control unit electrical connectors for damage, loose-fitting, corrosion, bent pins or contamination. Replace or repair any damaged connectors if necessary. When finished, reconnect the electrical connectors and check if the issue is resolved.

4. Check the taillight bulbs

On some cars, the ABS, Barke, Traction & Vehicle Stability Control (VSC) warning lights may come on if your taillight bulbs go out. I’ve seen this happen before on our Toyota Highlander Hybrid. Replace the bad bulbs and check if ABS warning light goes away.

5. Test ABS Relay

If you are getting error code C1114, check and if necessary replace ABS relay.

6. Active vs. Passive

There are two types of wheel speed sensors: active and passive. It is critical to know what type of sensor is used in your car in order to diagnose it properly. Passive ABS sensors are rarely used nowadays. Most of the newer cars have active wheel speed sensors.

7. Testing passive ABS sensors

There are two ways to test passive wheel speed sensors. First, you can remove the sensor and measure the resistance between the contact pins. Make sure that the measured resistance value is within an acceptable factory specified range. If resistance is too low or too hight, the sensor needs to be replaced.

Second, you can test the signal of the sensor using a digital multimeter. Unplug the sensor connector and attach the multimeter test leads to the connector pins. Spin the wheel and check if the sensor is generating electric current. The faster you spin the wheel, the higher the voltage you should see on the multimeter. Replace the sensor if you are not getting any output signal from it.

8. Testing active ABS sensors

Testing active ABS sensors is more challenging without costly specialized equipment, but it can be done using a common sense approach. I was able to do it on my Altima using just a regular digital multimeter, however, some of the issues require more advanced diagnosis.

9. Check wheel bearing and hub assembly

One of the reasons for ABS light can be a bad wheel bearing and hub assembly. I had this happen on my Lexus IS350. Replacing the bearing & hub assembly fixed the problem. You can read more about it in this article: Lexus IS/GS Front Wheel Bearing & Hub Assembly Replacement 2006-2015.