GM Service Manual Online
For 1990-2009 cars only

Refer to the Scan Tool Manual for complete information on scan tool diagnostics.

F0 - Diagnostic Trouble Codes (DTC)

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.
    • History Data: In this mode, DTC data is stored for the last 12 DTC events. This data includes the following information at the time when the DTC(s) was set:
       - The DTC number
       - Number of occurrences of the DTC
       - Number of ignition cycles since last occurrence
       - Was EBCM in an ABS mode when the DTC occurred
       - Composite vehicle speed (3 speed sensor inputs, averaged) when the DTC occurred
       - Was vehicle in an 4WD when the DTC occurred
       - Brake switch status
       - Differential Pressure switch status
    • Clear DTC Information: In this mode, current and history DTCs are cleared. History data is not cleared from the EBCM.

F1 - Data Display

The Data Display function contains two special function hot keys, and a data list which details ABS parameters. The hot keys perform the following functions:

    • DTCs -- used to instantly read stored DTCs
    • Quick Snap -- used to record instant events

The following ABS parameters are viewable on the data list:

    • Brake Switch Status--scan tool displays: On / Off
    • 4WD Status--scan tool displays: Two Wheel Drive or Four Wheel Drive
    • Left Front Wheel Speed--scan tool displays: km/h / mph--Display shows actual wheel speed. The default wheel speed is 3 mph.
    • Right Front Wheel Speed--scan tool displays: km/h / mph--Display shows actual wheel speed. The default wheel speed is 3 mph.
    • Rear Wheel Speed--scan tool displays: km/h / mph--Display shows actual wheel speed. The default wheel speed is 3 mph.
    • ABS Lamp Command--scan tool displays: On / Off
    • Brake Warning Lamp Cmd--scan tool displays: On / Off
    • Diff. Pressure Switch--scan tool displays: Ok / Low
    • DRP Active -- scan tool displays: Yes/No
    • ABS Stop State--scan tool displays: On/Off
    • ABS Pump Motor--scan tool displays: On/Off--This parameter indicates the state of the ABS Pump Motor.
    • ABS Relay Command--scan tool displays: On/Off--This parameter indicates the state of the ABS relay.
    • RF ISO Valve Command--scan tool displays: On/Off--This parameter indicates the state of the RF ISO Valve.
    • RF ISO Valve Feedback--scan tool displays: On/Off--This parameter indicates the state of the RF ISO Valve feedback.
    • LF ISO Valve Command--scan tool displays: On/Off--This parameter indicates the state of the LF ISO Valve feedback.
    • LF ISO Valve Feedback--scan tool displays: On/Off--This parameter indicates the state of the LF ISO Valve feedback.
    • Rear ISO Valve Command--scan tool displays: On/Off--This parameter indicates the state of the Rear ISO Valve.
    • Rear ISO Valve Feedback--scan tool displays: On/Off--This parameter indicates the state of the Rear ISO Valve feedback.
    • RF Dump Valve Command--scan tool displays: On/Off--This parameter indicates the state of the RF Dump Valve.
    • RF Dump Valve Feedback--scan tool displays: On/Off--This parameter indicates the state of the RF Dump Valve feedback.
    • LF Dump Valve Command--scan tool displays: On/Off--This parameter indicates the state of the LF Dump Valve.
    • LF Dump Valve Feedback--scan tool displays: On/Off--This parameter indicates the state of the LF Dump Valve feedback.
    • Rear Dump Valve Command--scan tool displays: On/Off--This parameter indicates the state of the Rear Dump Valve.
    • Rear Dump Valve Feedback--scan tool displays: On/Off--This parameter indicates the state of the Rear Dump Valve feedback.

F2 - 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. In a vehicle equipped with ABS, the Special Functions are grouped as following:

    • Function Test
    • Automated Bleed
    • ABS Motor
    • System Identification
    • Tire Size Calibration
    • ABS Lamp
    • Solenoid Tests (for all Dump and Isolation solenoid valves)
    • ABS Relay
    • Brake Lamp

Function Test

The Function Test cycles each valve solenoid and the pump motor (as well as the necessary relays) to check component operation. If a malfunction is detected, the EBCM will set DTC(s), 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 RUN.
  4. Select the scan tool's Special Functions.
  5. Select the Function Test.
  6. Run the Function Test.
  7. Note any DTCs set.

Automated Bleed

Automated Bleed cycles each valve solenoid and the pump motor in a special sequence (as well as the necessary relays) in order to bleed air out of the BPMV after removal or installation of brake lines, or BPMV replacement. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the Automated Bleed function.
  6. Run the Automated Bleed function.

ABS Motor

This function tests the ABS pump motor to check component operation. If a malfunction is detected, the EBCM will set DTC(s), and the ABS indicator lamp will turn on. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the ABS Motor Test.
  6. Run the ABS Motor Test.

System Identification

This function is used to identify the hardware and software revision of the EHCU

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select System Identification.
  6. Make note of the relevant information.

Tire Size Calibration

This function allows the EBCM tire size to be set or changed when a new EBCM is installed, or different tires/wheels are installed on the vehicle.

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the Tire Size Calibration.
  6. Make the necessary changes to existing tire size setting.

ABS Lamp

This test allows activation of the ABS indicator. The ABS Lamp test aids in diagnosing indicator malfunctions. The test allows the operator to turn the indicator on and off manually.

BRAKE Lamp

This test allows activation of the BRAKE indicator. The BRAKE Lamp test aids in diagnosing indicator malfunctions. The test allows the operator to flash the indicator on and off manually.

Solenoid Tests (Isolation Valves)

The Solenoid Test for isolation valves activates the selected wheel circuit Isolation 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 it in an attempt to allow it 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 RUN.
  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 the desired Isolation Solenoid test. Have an assistant command the Isolation valve ON 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 (Dump Valves)

The Solenoid Test for Dump valves activates the selected hydraulic wheel circuit Dump valve, placing it 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 valve to release hydraulic pressure to the affected brake caliper, 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 RUN.
  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 the desired Dump Solenoid Test. Have the assistant command the Dump valve ON 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.

ABS Relay

This function tests the ABS relay to check component operation. If a malfunction is detected, the EBCM will set DTC(s), and the ABS indicator lamp will turn on. Perform the test as follows:

  1. Ignition OFF.
  2. Install the scan tool.
  3. Turn ignition to RUN.
  4. Select the scan tool's Special Functions.
  5. Select the ABS Relay.
  6. Take note of the relay status as the relay is cycled.

F3 - Snapshot

In this test mode, the scan tool captures the data listed in the data displays before and after a snapshot. The following triggering conditions are available:

    • DTC -- In this mode, the snapshot will be triggered on a specific (operator selected) DTC.
    • Any DTC -- in this mode, the snapshot will trigger on any DTC
    • Auto Trigger -- will trigger a snapshot under two conditions:
        1. Wheel speed out of range -- Snapshot will trigger when a WSS/VSS input is +/- 11 km/h (7 mph) out of range in relation to other WSS/VSS inputs.
        2. ABS Stop -- Snapshot will trigger when an ABS event occurs.