To use this manual most effectively, a general understanding of basic electrical circuits and circuit testing tools is required. One should also be familiar with wiring diagrams and Ohm's law.

A careful visual and physical inspection must be part of every diagnostic routine. This can often identify a problem without further steps. Inspect all engine compartment and wheel speed sensor wiring for:

Inspect the vehicle tires for:

The visual inspection is very important. It must be done carefully.

Important: DTC charts should not be used unless a DTC is present.

Diagnostic trouble code (DTC) charts and function checks can help identify a faulty circuit or component through the process of elimination. These charts assume that the vehicle functioned properly at the time of assembly and that there are no multiple failures.

Important: ABS/TCS is disabled whenever the EBTCM is communicating with a Scan tool.

Important: Both current and history DTCs will clear when Clear DTCs is selected on the Scan tool.

Important: Disconnecting power to the ABS control module will clear current DTCs, but has no effect on history DTCs.

When the ABS control module detects a fault, it stores a DTC in the General Information table (current DTCs) and signals the BCM to command the I/P cluster to illuminate the ABS telltale. When the ignition is switched off, the current DTCs are moved to the Malf History table (history DTCs) and cleared from the General Information table.

Important: If an ABS control module is installed without activating the option bit, the DTC C0551 - Option Configuration Error will set and traction control will be disabled.

The correct engine and transmission option bit must be activated whenever a new ABS control module is installed. The Scan tool is required to complete this activation.

Observe parameters while:

Compare parameters with those on a known good system.

Important: ABS/TCS is disabled whenever the ABS telltale is on.

When ignition is switched on, the ABS control module performs a self-diagnostic routine while the I/P cluster performs a bulb-check by illuminating the ABS telltale for approximately 3 seconds. If the ABS control module detects a malfunction, it will ground circuit 867 to the BCM. The BCM will then use circuit 1807 (Class II Serial Data) to command the I/P cluster to keep the ABS telltale on. The telltale will remain on until the ignition is switched off.

The ABS control module (EBTCM) does NOT control the red brake telltale.

The LOW TRACTION telltale on the I/P cluster will come on whenever the TCS is in operation. The telltale will remain on for 3-4 seconds after the TCS event is complete. The telltale does NOT operate during an ABS event.

Clear the DTCs before performing any special tests with a Scan tool.

This test activates each valve solenoid, the pump motor and the appropriate relays. If the ABS control module detects a malfunction, the appropriate DTC will set and will display following the test. This test is the same routine as the ABS initialization sequence that occurs on every vehicle start.

1. Turn the ignition off.
2. Install a scan tool.
3. Turn the ignition to RUN.
4. Select the Scan tool's SPECIAL FUNCTIONS.
5. Select the AUTOMATED TEST.
6. Run the AUTOMATED TEST.
7. Note any DTCs that set.

This test allows the technician to place individual inlet valves into a pressure-hold position by activating its corresponding solenoid with the Scan tool. When in the pressure-hold position, the valve will not allow hydraulic pressure to the wheel circuit.

During an ABS event, the control module activates an inlet valve solenoid when it detects that a wheel is rotating too slow.

1. Turn the ignition off.
2. Install a Scan tool.
3. Raise the vehicle until the wheels are off the floor.
4. Turn the ignition to RUN.
5. Shift the transmission to NEUTRAL.
6. Select the Scan tool's SPECIAL FUNCTIONS.
7. Select the SOLENOID TEST.
8. Command the HOLD PRESSURE with the Scan tool.
9. Press and hold the brake pedal.
10. Have an assistant attempt to rotate the appropriate wheel by hand.

The inlet valve is OK if the wheel rotates.

This test allows the technician to place individual outlet valves into a pressure-release position by activating its corresponding solenoid with the Scan tool. When in the pressure-release position, the valve will allow hydraulic pressure in the wheel circuit to return to the master cylinder.

During an ABS event, the control module activates an outlet valve solenoid when a release of hydraulic pressure is needed because a wheel is rotating too slow. The inlet valve solenoid activation usually precedes this event.

1. Turn the ignition off.
2. Install the Scan tool.
3. Raise the vehicle until the wheels are off the floor.
4. Turn the ignition to RUN.
5. Shift the transmission to NEUTRAL.
6. Select the Scan tool's SPECIAL FUNCTIONS.
7. Select the SOLENOID TEST.
8. Command the PRESSURE RELEASE with the Scan tool.
9. Press and hold the brake pedal.
10. Have an assistant attempt to rotate the appropriate wheel by hand.

The outlet valve is OK if the wheel rotates.

This test allows the technician to flash the telltale on and off with the Scan tool.

1. Select the Scan tool's SPECIAL FUNCTION.
2. Select the LAMP TESTS.