GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Air Antilock Brake System 🢒 Status Lamps Illuminated - LFT, RER, and SEN

Circuit Description

As the wheel spins, the wheel speed sensor (WSS) produces an A/C signal. The electronic brake control module (EBCM) uses the frequency of the A/C signal to calculate the wheel speed.

Conditions for Running the Diagnostic Fault
    • The ignition is ON.
    • The vehicle speed is greater than 26 km/h (16 mph).

Conditions for Setting the Diagnostic Fault
    • Open WSS or WSS wiring.
    • Shorted WSS or WSS wiring.
    • Wheel speed signal not present or does not conform to design criteria.

Action Taken When the Diagnostic Fault Sets
    • The ABS indicator lamp turns ON.
    • The ABS is disables on that wheel only.
    • The EBCM illuminates the RER, LFT, and SEN LEDs.

Conditions for Clearing the Diagnostic Fault
    • Repair the condition responsible for illuminating the status lamps.
    • Perform the Status Lamps Reset Procedure.

Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:

    •  Testing for Intermittent Conditions and Poor Connections
    •  Connector Repairs
    •  Testing for Electrical Intermittents
    •  Wiring Repairs

If the customer concern is that the ABS indicator is on only during humid conditions such as rain, snow or vehicle wash, thoroughly inspect the WSS circuits for signs of water intrusion. Use the following procedure in order to help isolate the problem area:

  1. Spray the suspected area with a 5 percent salt water solution; 10 grams (2 teaspoons) of salt to 200 ml (12 oz) of water.
  2. Operate the vehicle at a speed greater than 19 km/h (12 mph) for at least 30 seconds.

Repair or replace the suspect harness if the DTC sets.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for the correct bearing play. Excessive bearing play can cause WSS air gap to exceed specification. WSS air gap must be reinspected after a repair is made to correct excessive bearing play.

    2.

  2. Measure the resistance value of the WSS in order to determine if the sensor has a valid resistance value.

    3.

  3. This step ensures the WSS is generating a valid A/C voltage output.

Step

Action

Values

Yes

No

Schematic Reference: Air Antilock Brake System Schematics

Connector End View Reference: Air Brake System Component Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Operate the vehicle at a speed greater than the specified value.
  2. Observe the LEDs on the electronic brake control module (EBCM).

Do the LEDs on the EBCM indicate a current wheel speed sensor (WSS) fault?

26 km/h (16 mph)

Go to Step 3

Go to Diagnostic Aids

3

  1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
  2. Inspect the wheel bearings for looseness or excessive wear and verify that the wheel bearing play is within specifications. Refer to Wheel Bearing Adjustment or Front Wheel Hub, Bearing, and Seal Replacement or Wheel Bearing Wear - Rear Drive Axle or Rear Axle Hub, Bearing, Cup, and/or Seal Replacement .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 4

4

Inspect the WSS in order to ensure the sensor is installed and retained properly for proper air gap. Refer to Front Wheel Speed Sensor Replacement or Rear Wheel Speed Sensor Replacement .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 5

5

  1. Disconnect the WSS harness connector.
  2. Use a DMM in order to measure the resistance across the WSS.

Does the resistance measure within the specified range?

1800-2200 ohms

Go to Step 6

Go to Step 8

6

  1. Spin the wheel by hand as fast as possible.
  2. Measure the A/C voltage across the WSS.

Does the A/C voltage measure greater than the specified value?

800 mV

Go to Step 7

Go to Step 8

7

Inspect for poor connections at the harness connector of the WSS. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8

Replace the WSS. Refer to Front Wheel Speed Sensor Replacement or Rear Wheel Speed Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

9

Test the WSS circuits for the following:

    • An open
    • A short to ground
    • A short to voltage
    • Shorted together

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step  10

10

Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

11

Replace the EBCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 12

--

12
  1. Perform the magnetic reset procedure. Refer to Status Lamp Resetting .
  2. Operate the vehicle within the Conditions for Running the Diagnostic Fault.

Do the same red LEDs illuminate?

--

Go to Step 3

Go to Step 13

13

Do any red LEDs illuminate?

--

Go to Diagnostic System Check - Vehicle

System OK