GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Tracker - 2WD 🢒 Brakes 🢒 Antilock Brake System 🢒 Scan Tool Diagnostics

The scan tool, when plugged into the DLC, becomes part of the vehicle's electronic system. The scan tool can perform the following functions:

    • Display ABS Data.
    • Display and clear ABS diagnostic trouble codes.
    • Control ABS components.
    • Perform extensive ABS diagnosis.
    • Provide diagnostic testing for intermittent ABS conditions.

Verify the proper system operation and the absence of DTCs after completing the clearing procedure.

In general the scan tool has five test modes for diagnosing the ABS.

    • ABS DATA - In this test mode, the scan tool continuously monitors wheel speed data, brake switch status and other inputs and outputs.
    • DTC(s) - In this test mode, diagnostic trouble codes stored by the EBCM, both current ignition cycle and history, may be displayed or cleared.
    • DTC HISTORY - In this mode, DTC history data is displayed. This data includes how many ignition cycles since the DTC occurred, along with other information for the last DTC set. The first three and last DTC set are included in the ABS history data.
    • SNAPSHOT - In this test mode, the scan tool captures data before and after a system malfunction (auto trigger) from a forced manual key press or from a DTC setting.
    • SPECIAL FUNCTIONS - In this test mode, the scan tool performs various functional tests to assist in problem isolation during troubleshooting.

ABS Data

A brief description of all ABS data parameters available on the scan tool are listed below:

    • Left Front Wheel Speed--scan tool displays: km/h/mph--Display shows actual wheel speed.
    • Right Front Wheel Speed--scan tool displays: km/h/mph--Display shows actual wheel speed.
    • Left Rear Wheel Speed--scan tool displays: km/h/mph--Display shows actual wheel speed.
    • Right Rear Wheel Speed--scan tool displays: km/h/mph--Display shows actual wheel speed.
    • Brake Switch--scan tool displays: Applied/Released--This parameter indicates the state of the brake switch.
    • Relay State--scan tool displays: On/Off--This parameter indicates the state of the relay.

Diagnostic Trouble Codes (DTCs)

The Diagnostic Trouble Codes (DTC) function has three modes that are described below:

    • DTC Information: In this mode, current or history DTC(s) stored by the EBCM can be displayed.
    • Enhanced Data: In this mode, DTC data for current or history DTC(s) is displayed. This data includes the following information at the time when the DTC(s) was set:
      • Brake switch status
      • ABS activity status
      • Vehicle speed
      • The number drive cycles since the DTC was set
    • Clear DTC Information: In this mode, current or history DTC(s) stored by the EBCM can be cleared.

Snapshot

In this test mode, the scan tool captures the data listed in the data displays before and after a snapshot triggering condition which may or may not set a DTC.

Special Functions

In this test mode, the scan tool can be used to perform functional tests on the ABS which help verify proper operation. Malfunction conditions can be further identified by testing and observing the test results. DTCs must be cleared before any tests in Special Functions can be performed. The Special Functions are grouped as following:

    • Lamp Test (ABS indicator)
    • Automated Test
    • Solenoid Tests (for all inlet and outlet solenoid valves)

Lamp Test

This test allows activation of the ABS warning indicator.

The Lamp Test aids in diagnosing indicator malfunctions. The test allows the operator to flash the indicator on and off manually.

Automated Test

The Automated Test cycles each valve solenoid and the pump motor (as well as the relay) to check component operation. If a malfunction is detected, the EBCM will set DTCs, which will be displayed upon completion of the test. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to ON.
  4. Select the scan tool's Special Functions.
  5. Select the Automated Test.
  6. Run the Automated Test.
  7. Note any DTCs set.

Solenoid Tests (Inlet Valves)

The Solenoid Test for inlet valves activates the selected wheel circuit Inlet valve placing it in the pressure hold position. When in the pressure hold position, the valve will not allow master cylinder pressure to be delivered to the hydraulic wheel circuit. This is done under ABS operating conditions because the EBCM has determined that the wheel is moving too slowly, so it holds additional master cylinder pressure from the wheel circuit in an attempt to allow the wheel to rotate at an appropriate speed. The scan tool commands the valve to close, which should allow the technician to spin the wheel even though an assistant is applying pressure to the brake pedal. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to ON.
  4. Raise vehicle such that wheels are about 6 inches off the floor with the transmission in neutral.
  5. Select the scan tool's Special Functions.
  6. Select Solenoid Test. Have an assistant command Hold Pressure with the scan tool.
  7. Have the assistant press and hold the brake pedal.
  8. Attempt to move the wheel being tested by hand; it should move even though the assistant is applying pressure to the brake pedal. The wheels may be difficult to turn by hand, but can be moved if the system is working properly.

Solenoid Tests (Outlet Valves)

The Solenoid Test for outlet valves activates the selected hydraulic wheel circuit valves, placing them in the pressure release position. When in the pressure release position, the valve will allow wheel caliper pressure to be returned to the master cylinder circuit. This is done under ABS operating conditions because the EBCM has determined that the wheel is moving too slowly, and holding additional master cylinder pressure from it has not allowed it to rotate at an appropriate speed. The scan tool commands the valves to these positions which should allow the technician to spin the wheel even though an assistant is applying pressure to the brake pedal. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to ON.
  4. Raise vehicle such that wheels are about 6 inches off the floor with the transmission in neutral.
  5. Have an assistant press and hold the brake pedal.
  6. Select the scan tools Special Functions.
  7. Select Solenoid Test. Have the assistant command Release Pressure with the scan tool.
  8. Attempt to move the wheel being tested by hand; it should move even though the assistant is applying pressure to the brake pedal. The wheels may be difficult to turn by hand, but can be moved if the system is working properly.