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 and ETS Data. |
| • | Display and clear ABS diagnostic trouble codes. |
| • | Control ABS components. |
| • | Perform extensive ABS diagnosis. |
| • | Provide diagnostic testing for intermittent ABS conditions. |
In general the scan tool has six 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. |
| • | ETS DATA - In this test mode, the scan tool
continuously monitors wheel speed data, ETS 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. |
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: |
| • | The number of 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:
| • | Solenoid Tests (for all inlet and outlet solenoid valves) |
Automated Bleed
The Automated Bleed mode of the scan tool is used during bleeding of
the ABS system. Refer to
Antilock Brake System Automated Bleed Procedure
.
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:
- Ignition OFF.
- Install the scan tool.
- Turn the ignition ON.
- Raise the vehicle such that the wheels are about 6 inches off
the floor with the transmission in neutral.
- Select the scan tool's Special Functions.
- Select Solenoid Test. Have an assistant command Hold Pressure
with the scan tool.
- Have the assistant press and hold the brake pedal.
- 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 caliper or wheel
cylinder 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:
- Ignition OFF.
- Install the scan tool.
- Turn the ignition ON.
- Raise the vehicle such that the wheels are about 6 inches off
the floor with the transmission in neutral.
- Have an assistant press and hold the brake pedal.
- Select the scan tools Special Functions.
- Select Solenoid Test. Have the assistant command Release Pressure
with the scan tool.
- 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.
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:
- Ignition OFF.
- Install the scan tool.
- Turn the ignition ON.
- Select the scan tool's Special Functions.
- Select the Automated Test.
- Run the Automated Test.
- Note any DTCs set.
