Antilock Brake System Buick Century VI

Fastener Tightening Specifications

Fastener Tightening Specifications

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Scheme 10

Scheme 11

Scheme 12

Scheme 13

Scheme 14

Scheme 15

Begin the system diagnosis with DIAGNOSTIC SYSTEM CHECK - ABS . The Diagnostic System Check will provide the following information

1. The identification of the control modules which command the system
2. The ability of the control modules to communicate through the serial data circuit
3. The identification of any stored diagnostic trouble codes (DTCs) and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Circuit Description

The ABS Diagnostic System Check is an organized approach to identify problems associated with the EBCM. This check must be the starting point for any EBCM complaint, and will direct you to the next logical step in diagnosing the complaint.

The EBCM is a very reliable component and is not likely the cause of the malfunction. Most system complaints are linked to faulty wiring, connectors, and occasionally to components. Understanding the ABS system and using the tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.

Test Description

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

1. 2. Lack of communication may be due to a partial malfunction of the serial data circuit or due to a total malfunction of the serial data circuit. The specified procedure will determine the particular condition.
2. 4. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

Scheme 16

Scheme 17

Scheme 18

Scheme 19

Scheme 20

Scheme 21

Scheme 22

Scan Tool Data Definitions

ABS Active: The scan tool displays Yes or No. The active status of the ABS. Indicates if the ABS is currently active.

ABS Relay Command: The scan tool displays On or Off. The scan tool displays On during vehicle operation. The EBCM commands the ABS relay On when ignition positive voltage is present.

ABS Relay Feedback: The scan tool displays On or Off. The scan tool displays On during vehicle operation.

ABS Warning Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the ABS indicator.

Antilock Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the ABS active indicator ON.

Auto Learn Mode Active: The scan tool displays Yes or No. Indicates if TIM is currently in learn mode.

Battery Voltage: The scan tool displays 0 to 30 Volts. The voltage measured between the module's battery positive voltage circuit and ground circuit.

Brake Fluid Level: The scan tool displays Low or Normal. The scan tool displays if the brake fluid level is below the standard operating level.

Brake Switch Status: The scan tool displays Applied or Released. The scan tool displays the state of the brake switch.

Brake Temp Status: The scan tool displays Normal or Over Temp. The status of the brake temperature. Indicates if the brake temperature is above the traction control thermal cutoff point. If brake temperatures are above the thermal cutoff point, Over Temp is displayed and traction control is temporarily suspended until the brake temperature cools below the cutoff. This feature is used to maintain braking effectiveness if the base braking system is required. Over-heated brakes could result in brake fade.

Configuration ID: The scan tool displays the 4-digit configuration ID of the control module.

DE Base Part Number: The scan tool displays the base part number of the EBCM.

DE Build Sequence Number: The scan tool displays the number in order that the EBCM was built.

DE Calibration Part Number: The scan tool displays the calibration part number of the EBCM.

DE End Model Part Number: The scan tool displays the end model part number of the EBCM.

DE ROM Part Number: The scan tool displays the ROM part number of the EBCM.

DRP Active: The scan tool displays Yes or No. The active status of the DRP indicates if DRP is currently active.

DRP Disabled: The scan tool displays Yes or No. The failed status of the DRP indicates if the EBCM disabled DRP due to a malfunction.

DRP Equipped: The scan tool displays Yes or No. Indicates if the vehicle is equipped with DRP.

DRP Switched Battery Voltage: The scan tool displays 0 to 17 volts. The level of the internal EBCM switched battery voltage available to the solenoid valves and pump motor.

EBCM to PCM Requested: The scan tool displays 0-100 percent. The scan tool displays the torque signal. The signal is used to transmit how much torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 100 percent. The signal should be at 100 percent when the traction control is not active and at lower values when the traction control is active.

ETS Active: The scan tool displays Yes or No. The scan tool displays whether or not the vehicle is currently in an ETS event.

ETS Active Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the LOW TRAC indicator ON.

ETS Disable Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the TRAC OFF indicator ON.

ETS Equipped: The scan tool displays Yes or No. Indicates if the vehicle is equipped with ETS.

ETS Status: The scan tool displays Off or On. The scan tool displays the state of the ETS based on if the driver has disabled ETS by pressing the ETS switch, or if the ETS has been disabled due to a malfunction.

ETS Warning Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the TRAC OFF indicator ON.

Ignition 0: The scan tool displays 0-17 Volts. The scan tool displays the level of ignition positive voltage at the IPC.

Ignition Voltage: The scan tool displays 0 to 17 volts. The level of ignition voltage at the EBCM.

Julian Date Code: The scan tool displays year and day. The first digit indicates the last digit of the year that the EBCM was built. The remaining 3 digits indicate the day of the year that the EBCM was built.

Left Front Wheel Speed: The scan tool displays 0 to 255 km/h (0 to 159 mph). The actual speed of the left front wheel.

Left Rear Wheel Speed: The scan tool displays 0 to 255 km/h (0 to 159 mph). The actual speed of the left front wheel.

LF Inlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the LF inlet solenoid valve.

LF Outlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the LF outlet solenoid valve.

LF Rotor Temperature: The scan tool displays -40 to +650°C (-40 to +1202°F). The estimated temperature of the left front brake rotor.

Low Tire Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the low tire pressure indicator ON.

Low Tire Reset: The scan tool displays Was Pressed. Indicates if the tire pressure reset switch was pressed.

Low Trac. Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the LOW TRAC Indicator ON.

Low Tire Pressure: The scan tool displays Yes or No. Indicates if the EBCM has determined that a tire has low pressure.

LR Inlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the LR inlet solenoid valve.

LR Outlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the LR outlet solenoid valve.

Monitor Mode 1: The scan tool displays Yes or No. Indicates if TIM is currently in mode 1 monitoring. The EBCM has limited detection capability for a low tire condition and has only partially learned the tire inflation configuration for the speed range.

Monitor Mode 2: The scan tool displays Yes or No. Indicates if TIM is currently in mode 2 monitoring. The EBCM has full detection capability for a low tire condition and has fully learned the tire inflation configuration for the speed range.

PCM to EBCM Delivered: The scan tool displays 0-100 percent. The scan tool displays the Requested Torque signal. The signal is used to transmit how much engine torque the PCM is delivering. Normal values are between 10 and 100 percent. The signal is at low values at idle and at higher values under driving conditions.

PROM ID: The scan tool displays the 4 digit PROM ID of the EBCM.

Pump Motor Commanded State: The scan tool displays Off or On. Indicates the commanded state of the pump motor control.

Pump Motor Feedback State: The scan tool displays Off or On. Indicate the actual state of the pump motor control.

Red Brake Lamp: The scan tool displays Off or On. Indicates if the red Brake warning indicator is currently ON.

RF Inlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the RF inlet solenoid valve.

RF Outlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the RF outlet solenoid valve.

RF Rotor Temperature: The scan tool displays -40 to 650°C (-40 to 1202°F). The estimated temperature of the right front brake rotor.

Right Front Wheel Speed: The scan tool displays 0 to 255 km/h (0 to 159 mph). The actual speed of the right front wheel.

Right Rear Wheel Speed: The scan tool displays 0 to 255 km/h (0 to 159 mph). The actual speed of the right rear wheel.

Rough Road Parameter: The scan tool displays 0 to 1 g. The EBCM calculation of the road surface, this information is sent to the PCM over the class 2 serial data line. The PCM uses this information for misfire detection.

RR Inlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the RR inlet solenoid valve.

RR Outlet Valve Solenoid: The scan tool displays Active or Inactive. The scan tool displays the commanded state of the RR outlet solenoid valve.

Software Part Number: The scan tool displays the software version of the BCM.

Software Version: The scan tool displays the software version of the IPC.

Switched Battery Voltage: The scan tool displays 0 to 17 volts. The level of the internal EBCM switched battery voltage available to the solenoid valves and pump motor.

System ID: The scan tool displays the configuration ID of the EBCM.

TCS Active: The scan tool displays Yes or No. The active status of the TCS. Indicates if TCS is currently active.

TCS Active Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the Traction Active indicator ON.

TCS Circuit History: The scan tool displays history status of the requested torque signal circuit.

TCS Circuit Status: The scan tool displays OK or Fault. The status of the delivered torque signal circuit.

TCS Disable Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the TRAC OFF indicator ON.

TCS Enable Status: The scan tool displays Off or On. The scan tool displays the state of the TCS based on if the driver has disabled TCS by pressing the Traction Control switch, or if the TCS is disabled because of a malfunction.

TCS Equipped: The scan tool displays Yes or No. Indicates if the vehicle is equipped with TCS.

TCS Failed: The scan tool displays Yes or No. The failed status of the TCS. Indicates if the EBCM disabled TCS due to a malfunction.

TCS Switch: The scan tool displays Was Pressed. Indicates if the traction control switch was pressed.

TCS Warning Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the Traction Off indicator ON.

TIM Equipped: The scan tool displays Yes or No. The scan tool displays if vehicle is equipped with TIM.

TIM Failed: The scan tool displays Yes or No. Indicates if TIM failed due to a malfunction.

TIM Reset Switch: The scan tool displays Was Pressed. Indicates if the TIM reset switch was pressed.

Torque Delivered Signal: The scan tool displays 0 to 100%. The duty cycle of the delivered torque signal. The duty cycle of the signal is used to transmit how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal is at low values (approximately 10 percent) at idle and at higher values under driving conditions.

Torque Request Signal: The scan tool displays 0 to 100%. The duty cycle of the requested torque signal. The duty cycle of the signal is used to transmit how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal is at 90 percent duty cycle when traction control is not active and at lower values (approximately 10 percent) when traction control is active.

Traction Control: The scan tool displays Active or Inactive. The active status of the TCS. Indicates if TCS is currently active.

Traction Control Status: The scan tool displays Active or Inactive. The active status of the TCS. Indicates if TCS is currently active.

Traction Off Lamp: The scan tool displays Off or On. Indicates if the EBCM is commanding the TRAC OFF indicator ON.

Vehicle Speed: The scan tool displays 0-255 km/h (0-158 mph). This parameter displays the vehicle speed. The Powertrain Control Module (PCM) receives reference pulses from the Vehicle Speed Sensor (VSS) and converts them into km/h or MPH for display.

VES Actuator Commanded: Displays -3.3 to +3.3 amps. The amount of current that the EBCM is commanding to the variable effort steering actuator.

VES Actuator Feedback: Displays -3.3 to +3.3 amps. The actual amount of current that the variable effort steering actuator is drawing from the EBCM. The scan tool display the absolute value (i.e. positive value) of the feedback current.

VES Equipped: The scan tool displays Yes or No. The scan tool displays if vehicle is equipped with VES.

Diagnostic Trouble Code (DTC) List

DIAGNOSTIC TROUBLE CODE (DTC) LIST

Scheme 23

History Data

Enhanced diagnostic information is found in the History Data function of the scan tool. Enhanced diagnostic information provides the service technician with specific malfunction occurrence information.

The scan tool will display the last 3 DTCs to occur, one at a time. The DTC with the most recent occurrence will be displayed first. Each DTC will include the following

1. The number of drive cycles since the DTC last occurred.
2. The number of occurrences for the DTC since the scan tool DTC information was last cleared.

The most recent DTC will also display various data parameters with values from the time of the DTC occurrence.

Diagnostic Strategy

In difficult diagnostic situations use the above information to identify malfunction occurrence trends. Ask question such as the following

1. Did the malfunction only occur once over a large number of drive cycles, indicating an unusual condition present when it occurred?
2. Does the malfunction occur infrequently over a large number of drive cycles, indicating that special diagnostic techniques may be required to identify the source of the malfunction?

A malfunction that occurs more frequently increases the odds of finding the cause of the malfunction.

Use the information in order to determine if a DTC is intermittent. Use the information in order to determine if the DTC has not set for long periods of time due to weather changes or a repair prior to this visit.

The Traction Off indicator is controlled by the instrument cluster via serial data messages from the EBCM. When the body control module sees the traction control switch input grounded through the momentary traction control switch, it sends a serial data message to the EBCM that tells the EBCM that the traction control switch has been pressed. The EBCM then disables traction control and sends a serial data message to the instrument cluster to turn the Traction Off indicator ON. Each time the ignition is cycled from OFF to ON, the traction control system is enabled.

The following conditions will cause the Traction Off indicator to illuminate

1. The EBCM has disabled the TCS due to a DTC.
2. The driver manually disabling the TCS via the traction control switch.
3. The instrument cluster bulb check. When the ignition switch is turned to ON, the Traction Off indicator will turn on for approximately 3 seconds and then turn OFF.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The BCM detects a ground on the traction control switch signal circuit for longer than 60 seconds.

Action Taken When the DTC Sets

1. The ABS remains functional.
2. The ABS indicator remains OFF.

Conditions for Clearing the DTC

1. The condition for the DTC is no longer present and you used the scan tool Clear DTC function.
2. The BCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive ignition cycles.

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

1. 2. Tests for the normal state of the TCS switch using a scan tool.
2. 3. Tests if the BCM is able to detect a change in TCS switch state.
3. 4. Tests for a stuck or shorted TCS switch. If the TCS switch is stuck or shorted, the state will change from On to Off when the TCS switch is disconnected.
4. 5. Tests for a short to ground in the TCS switch signal circuit.
5. 8. When the BCM is replaced, use a scan tool to perform the setup procedure for the BCM. Refer to BODY CONTROL MODULE (BCM) PROGRAMMING/RPO CONFIGURATION in Body Control System.

Scheme 24

The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage.

The EBCM controls each solenoid valve by grounding the solenoid.

The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes

1. Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events.
2. Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.

1. The ignition voltage is greater than 10.8 volts.
2. The system relay is commanded ON.
3. For Criteria 2, one of the following conditions exists: The pump motor is OFF. During initialization, the pump motor is ON.

One of the following conditions exists for 0.23 seconds

Criteria 1

The system voltage is less than 8 volts.

Criteria 2

The difference between the ignition voltage and system voltage is greater than 1.9 volts.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids

The system relay is integral to the EBCM. The relay is not serviceable.

The number below refers to the step number on the diagnostic table.

1. 2. Determines whether the DTC is current.

Scheme 25

The EBCM monitors the On/Off state of each solenoid and recognizes when the ABS is in pressure decrease too long. This fault indicates that the EBCM was unable to decrease brake pressure enough to a certain wheel to prevent excessive wheel slip.

1. The ABS is active.
2. The wheel speed is less than 5 km/h (3 mph).

The solenoid of the wheel is releasing for greater than 1 second.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The ABS indicator turns ON.
4. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Possible causes of this DTC are the following conditions

1. A contaminated hydraulic unit.
2. An intermittent wheel speed sensor.
3. A sticking solenoid.
4. Excessive brake drag or high resistance in base brake system.
5. Suspension system irregularities.

Scheme 26

The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage.

The EBCM controls each solenoid valve by grounding the solenoid.

The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes

1. Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events.
2. Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.

1. The pump motor has been commanded OFF for 1 second.
2. The system voltage is greater than 9.36 volts.

One of the following conditions exists for 0.2 seconds

1. The voltage across the pump motor is greater than 10.2 volts.
2. The pump motor low side voltage is less than 2.7 volts.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

1. This DTC determines if there is a short in the pump motor control circuit.
2. The pump motor is integral to the BPMV. The pump motor is not serviceable.

The number below refers to the step number on the diagnostic table.

1. 3. Tests the pump motor circuits of the BPMV for a short to the housing of the BPMV.

Scheme 27

The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage.

The EBCM controls each solenoid valve by grounding the solenoid.

The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes

1. Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events.
2. Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.

1. The pump motor is commanded ON.
2. The system voltage is greater than 8 volts.

One of the following conditions exists for 0.16 seconds

1. With the commanded pump motor voltage less than the system voltage, the actual pump motor voltage is 3 volts less than the commanded voltage.
2. With the commanded pump motor voltage greater than the system voltage, the actual pump motor voltage is less than 8 volts.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

The pump motor is integral to the BPMV. The pump motor is not serviceable.

The number below refers to the step number on the diagnostic table.

5. Tests the ability of the EBCM to control the pump motor. If the test lamp illuminates, the pump motor circuit within the EBCM is good.

Scheme 28

As the wheel spins, the wheel speed sensor produces an AC signal. The EBCM uses the frequency of the AC signal to calculate the wheel speed.

C1221 through C1228

1. DTCs C1232 through C1235 are not set.
2. The brake pedal is not pressed.
3. The ABS is not active.

C1232 through C1235

The ignition is ON.

C1221 through C1224

All of the following conditions exists for 2.5 seconds

1. The suspect wheel speed equals zero.
2. The other wheel speeds are greater than 8 km/h (5 mph).
3. The other wheel speeds are within 11 km/h (7 mph) of each other.

C1225 through C1228

The EBCM detects a rapid variation in the wheel speed. The wheel speed changes by 24 km/h (14.9 mph) or more in 0.01 second. The change must occur 5 times with no more than 1 second between occurrences.

One of the following conditions exists for 0.02 seconds

1. A short to voltage - the wheel speed sensor signal circuit and wheel speed sensor return circuit voltages are both greater than 4.25 volts.
2. A short to ground - the wheel speed sensor signal circuit and wheel speed sensor return circuit voltages are both less than 0.75 volts.
3. An open - the wheel speed sensor signal circuit voltage is greater than 4.25 volts and wheel speed sensor return circuit voltage is less than 0.75 volts.

If equipped, the following actions occur

1. The EBCM disables the ABS/TCS for the duration of the ignition cycle.
2. The EBCM temporarily suspends the TIM monitoring function while the DTC is set.
3. The DRP does not function optimally.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Under the following conditions, 2 Wheel Speed Sensor Input is 0 DTCs are set

1. The 2 suspect wheel speeds equal zero for 20 seconds.
2. The other wheel speeds are greater than 16 km/h (10 mph).
3. The other wheel speeds are within 11 km/h (7 mph) of each other.

Diagnose each wheel speed sensor individually.

A possible cause of this DTC is electrical noise on the wheel speed sensor harness wiring. Electrical noise could result from the wheel speed sensor wires being routed to close to high energy ignition system components, such as spark plug wires.

If the customer comments that the ABS indicator is ON only during moist environmental conditions: rain, snow, vehicle wash, etc., inspect the wheel speed sensor wiring for signs of water intrusion. If the DTC is not current, clear all DTCs and simulate the effects of water intrusion by using the following procedure

1. Spray the suspected area with a 5 percent saltwater solution. To create a 5 percent saltwater solution, add 2 teaspoons of salt to 8 fl oz of water (10 g of salt to 200 ml of water).
2. Test drive the vehicle over various road surfaces: bumps, turns, etc., above 40 km/h (25 mph) for at least 30 seconds.
3. If the DTC returns, replace the suspected wheel speed sensor or repair the wheel speed sensor wiring.
4. Rinse the area thoroughly when completed.

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

4. Measures the resistance of the wheel speed sensor in order to determine if the sensor has a valid resistance value.

5. Ensures that the wheel speed sensor is generating a valid AC voltage output.

Scheme 29

The EBCM monitors the voltage level available for system operation. A low voltage condition prevents the system from operating properly.

1. The vehicle speed is greater than 8 km/h (5 mph).
2. The ignition voltage is less than 10.8 volts.
3. The system relay is commanded ON.

One of the following conditions exists for 0.72 seconds

1. During initialization or when the system is inactive, the system voltage is less than 10.8 volts.
2. During the system operation, the system voltage is less than 9.36 volts.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

1. Test the charging system. Refer to DIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL in Battery.
2. Possible causes of this DTC are the following conditions: A charging system malfunction An excessive battery draw A weak battery A faulty system ground

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

1. 2. Use the scan tool in order to inspect the voltage to the EBCM.
2. 3. Use the scan tool in order to inspect the voltage to the body control module. A low voltage value in multiple modules indicates a concern in the charging system.
3. 5. Verifies that the condition is still present.

Scheme 30

The EBCM monitors the voltage level available for system operation. If the voltage level is too high, damage may result in the system. When the EBCM detects a high voltage condition, the EBCM turns OFF the system relay which removes battery voltage from the solenoid valves and pump motor.

The vehicle speed is greater than 8 km/h (5 mph).

The system voltage is greater than 17 volts for 0.7 seconds.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

A possible cause of this DTC is overcharging.

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

1. 2. Use the scan tool in order to inspect the voltage to the EBCM.
2. 3. Use the scan tool in order to inspect the voltage to the body control module. A low voltage value in multiple modules indicates a concern in the charging system.
3. 4. Verifies that the condition is still present.

Scheme 31

The EBCM monitors vehicle speed deceleration, system activation, and stoplamp switch active times in order to calculate an estimate of the brake rotor temperatures. If the EBCM calculates that the brake rotor temperatures have exceeded the thermal cutoff point, the EBCM will temporarily suspend the TCS function until the brake rotors cool. This feature is used to maintain braking effectiveness if normal base braking is required. An overly heated brake system could result in brake fade.

The EBCM continues calculating the brake rotor temperatures after the ignition is turned OFF. The EBCM remains awake until the EBCM calculates that the brake rotors cooled sufficiently. The cooling period may take up to 30 minutes.

The ABS conditions and the braking conditions are normal.

This DTC sets when the estimated brake rotor temperature of either of the drive wheels exceeds 375°C (700°F). When the estimated brake rotor temperature of either of the drive wheels exceeds 375°C (700°F) during normal braking or normal ABS operations, the DTC does not set until the next TCS activation. The brake rotor temperature can exceed 375°C (700°F) without setting the DTC if a TCS activation has not occurred. When the estimated brake rotor temperature of either of the drive wheels exceeds 375°C (700°F) during a TCS activation, the DTC sets immediately, but the EBCM does not disable TCS until the end of the TCS event.

1. The EBCM disables the TCS until the DTC becomes a history DTC.
2. The Traction Off indicator turns ON.
3. The ABS remains functional.

1. The current DTC becomes history when the estimated brake rotor temperatures of both drive wheels decreases below 275°C (530°F). The EBCM also enables TCS.
2. The condition for the DTC is no longer present and you used the scan tool Clear DTC function.
3. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

1. With TCS temporarily disabled, the EBCM continues calculating the brake rotor temperatures after the ignition is turned OFF. Turning ON the ignition again while TCS is temporarily disabled will not re-enable TCS.
2. The temperature is an estimate calculated by the EBCM.
3. Possible causes of this DTC are the following conditions: The brake usage is excessive. The TCS usage is excessive. The stoplamp switch is misaligned or damaged.

The number below refers to the step number on the diagnostic table.

4. Use the scan tool in order to verify that the Brake Thermal Model is exceeded.

Scheme 32

The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage.

The EBCM controls each solenoid valve by grounding the solenoid.

The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes

1. Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events.
2. Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.

C1242

1. The system voltage is greater than 8.0 volts.
2. The system relay is ON.
3. The pump motor is commanded OFF.

C1243

1. The pump motor is ON for at least 0.3 seconds.
2. The system relay is ON.

The voltage across the pump motor is between 1.7 - 10.2 volts for 2 seconds.

The pump motor is stalled or turning slowly.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

The pump motor is integral to the BPMV. The pump motor is not serviceable.

The number below refers to the step number on the diagnostic table.

5. Tests the ability of the EBCM to control the pump motor. If the test lamp illuminates, the pump motor circuit within the EBCM is good.

Scheme 33

The dynamic rear proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the mechanical proportioning valve in the base brake system. The DRP control system is part of the operating software in the EBCM. The DRP uses active control with the existing ABS in order to regulate the vehicle's rear brake pressure.

One or more faults have been detected by the EBCM in the ABS/TCS systems.

One of the following conditions exits

1. DTC C1236 sets and ignition voltage is less than 8.5 volts.
2. DTC C1254 or C1255 sets.
3. DTC C1265 and C1267 set.
4. Two wheel speed sensor DTCs on the same axle set.

1. The EBCM disables the DRP for the duration of the ignition cycle.
2. The red Brake warning indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

1. Use this DTC in order to differentiate which of the following conditions is present: The EBCM turned ON the red Brake warning indicator. The instrument cluster turned ON the red Brake warning indicator due to low brake fluid in the master cylinder reservoir. The body control module turned ON the red Brake warning indicator due to the application of the park brake. Diagnose any other ABS DTCs that set along with this DTC.

The number below refers to the step number on the diagnostic table.

1. 2. Verifies whether other ABS/TCS DTCs are set.

Scheme 34

The microprocessor contains a data storage area, keep alive memory, which can save pertinent data when the ignition is turned OFF. The keep alive memory (KAM) data is lost if battery power or module ground is removed from the module. The KAM area is an integral part of the microprocessor and cannot be serviced separately.

The ABS conditions and the braking conditions are normal.

The microprocessor calculates a checksum on those areas of memory that hold critical operation data. This is done at a regular interval and is called the periodic checksum. The microprocessor also calculates a checksum on these memory locations when ever new data is written to them. This is called the running checksum.

To check the keep alive memory (KAM), the microprocessor compares the periodic checksum to the running checksum. If they do not match, the microprocessor sets the DTC.

If equipped, the following actions occur

1. The EBCM disables the DRP/ABS/TCS for the duration of the ignition cycle.
2. The EBCM disables the variable effort steering (VES) for the duration of the ignition cycle.
3. The ABS indicator turns ON.
4. The Traction Off indicator turns ON.
5. The EBCM will not send serial data messages.
6. The EBCM will not send the requested torque output to the PCM.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Possible causes of this DTC are the following conditions

1. A loss of battery ground
2. A disconnected battery
3. A running reset A running reset is detected when the keep alive memory check sum is not updated properly.
4. A sudden drop in the system voltage to less than 5 volts
5. Long extended engine cranks that cause the battery voltage to drop
6. Poor power or ground connections
7. An internal EBCM malfunction

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

1. 2. Tests for an open in the ground circuits of the body control module.
2. 4. Verifies the proper operation of the charging system.
3. 6. Determines whether the DTC resets.

Scheme 35

This DTC identifies a malfunction within the EBCM.

The ABS conditions and the braking conditions are normal.

An internal EBCM malfunction exists.

C1255

If equipped, the following actions occur

1. The EBCM disables the DRP/ABS/TCS for the duration of the ignition cycle.
2. The EBCM disables the variable effort steering (VES) for the duration of the ignition cycle.
3. The EBCM temporarily suspends the TIM monitoring function while the DTC is set.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

C1256

1. The ABS remains functional.
2. The ABS indicator remains OFF.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

The scan tool displays 2 additional characters after the DTC. Take note of the 2 character code and any other DTCs that are set. The 2 character code is an engineering aid used in order to determine the cause of the internal malfunction.

The number below refers to the step number on the diagnostic table.

1. 2. Determines whether the DTC is current.

Scheme 36

The system relay is energized when the ignition is ON. The system relay supplies voltage to the valve solenoids and the pump motor. This voltage is referred to as the system voltage. The EBCM microprocessor activates the valve solenoids by grounding the control circuit.

1. The system voltage is greater than 8 volts.
2. The ignition voltage is greater than 9 volts.

The commanded state of the driver and the actual state of the control circuit do not match for 0.03 seconds.

If equipped, the following actions occur

1. The EBCM disables the ABS for the duration of the ignition cycle.
2. The EBCM disables the TCS (w/NW9) for the duration of the ignition cycle.
3. The DRP does not function optimally, or with ignition voltage less than 8.5 volts, the EBCM disables the DRP for the duration of the ignition cycle.
4. The ABS indicator turns ON.
5. The Traction Off indicator turns ON.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

The solenoid valve circuit is internal to the EBCM. The solenoid valve circuit is not diagnosable external to the EBCM. The DTC sets when there is a malfunction in the solenoid circuit internal to the EBCM.

The number below refers to the step number on the diagnostic table.

1. 2. Determines whether the DTC is current.

Scheme 37

The PCM monitors various parameters and will not allow traction control operation if any parameter falls outside a specified range.

Condition for Running the DTC

The ignition is ON.

The PCM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The PCM will typically set a DTC and the EBCM will set this DTC.

1. The EBCM disables the TCS until the DTC becomes a history DTC.
2. The Traction Off indicator turns ON.
3. The ABS remains functional.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system.

Scheme 38

The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.

The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.

The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.

When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

The engine is running.

C1276

One of the following conditions exists

1. The EBCM detects that delivered torque signal is out of the valid range.
2. The EBCM does not receive the delivered torque signal.

P1644 or P1689

The PCM detects that the delivered torque signal voltage is invalid.

1. The EBCM disables the TCS for the duration of the ignition cycle.
2. The PCM will store conditions which were present when the DTC set as Fall Records data only.
3. The Traction Off indicator turns ON.
4. The ABS remains functional.

1. The condition for the DTC is no longer present and you used the scan tool Clear DTC function.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
3. The PCM automatically clears the history DTC when a current DTC is not detected in 40 consecutive warm-up cycles.

The following conditions can cause this concern

1. An open in the delivered torque circuit.
2. An short to ground or voltage in the delivered torque circuit.
3. A wiring problem, terminal corrosion, or poor connection in the delivered torque circuit.
4. A communication frequency problem.
5. A communication duty cycle problem.
6. The EBCM is not receiving information from the PCM.
7. Loose or corroded EBCM ground or PCM ground.

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

3. Use the scan tool in order to determine if the delivered torque signal has a valid duty cycle.

9. This vehicle is equipped with a PCM which uses an Electrically Erasable Programmable Read Only Memory (EEPROM). When replacing the PCM, the replacement PCM must be programmed.

Scheme 39

The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.

The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.

The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.

When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

The engine is running.

C1277

The PCM diagnoses the requested torque signal circuit and sends a serial data message to the EBCM indicating a fault is present.

P1571

One of the following conditions exists

1. The PCM detects that requested torque signal is out of the valid range.
2. The PCM does not receive the requested torque signal.

1. The EBCM disables the TCS for the duration of the ignition cycle.
2. The PCM will store conditions which were present when the DTC set as Fail Records data only.
3. The Traction Off indicator turns ON.
4. The ABS remains functional.

1. The condition for the DTC is no longer present and you used the scan tool Clear DTC function.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
3. The PCM automatically clears the history DTC when a current DTC is not detected in 40 consecutive warm-up cycles.

The following conditions can cause this concern

1. An open in the delivered torque circuit.
2. An short to ground or voltage in the delivered torque circuit.
3. A wiring problem, terminal corrosion, or poor connection in the delivered torque circuit.
4. A communication frequency problem.
5. A communication duty cycle problem.
6. The EBCM is not receiving information from the PCM.
7. Loose or corroded EBCM ground or PCM ground.

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

3. Use the scan tool in order to determine if the requested torque signal has a valid duty cycle.

4. Measure the requested torque signal in order to determine if the signal has a valid duty cycle.

5. Measure the requested torque signal in order to determine if the signal has a valid frequency.

11. This vehicle is equipped with a PCM which uses an Electrically Erasable Programmable Read Only Memory (EEPROM). When replacing the PCM, the replacement PCM must be programmed.

Scheme 40

Scheme 41

The PCM monitors various parameters and will not allow traction control operation if any parameter falls outside a specified range.

The ignition is ON.

The PCM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The PCM will typically set a DTC and the EBCM will set this DTC.

1. The EBCM disables the TCS for the duration of the ignition cycle.
2. The Traction Off indicator turns ON.
3. The ABS remains functional.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system.

Scheme 42

The stop lamp switch signal informs the EBCM when the brake pedal is pressed.

The ABS conditions and the braking conditions are normal.

1. The stop lamp switch remains open for 3 deceleration cycles.
2. A DTC C1291 was set in a previous ignition cycle.

1. The EBCM disables the TCS for the duration of the ignition cycle.
2. The Traction Off indicator turns ON.
3. The ABS remains functional.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

1. Diagnose any wheel speed sensor DTCs before continuing with the diagnosis of the DTC.
2. A deceleration cycle consists of the following sequence: The vehicle speed is greater than 24 km/h (15 mph). The vehicle decelerates more than 8 km/h/second (5 mph/second) for 2 seconds. The vehicle speed decelerates to less than 16 km/h (10 mph).
3. Verify proper stop lamp switch operation using the data list of the scan tool. As the brake is applied, the data list displays the stop lamp switch on within 2.54 cm (1 in) of travel.
4. Possible causes of this DTC are the following conditions: An open stop lamp switch The stop lamp switch is misadjusted An open fuse Circuit has a wiring problem, terminal corrosion, or poor connections Erratic wheel speeds

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

3. Tests the circuit for a change in states.

5. Tests for proper operation of the circuit by bypassing the stop lamp switch. If the fuse in the jumper opens when you perform this test, the signal circuit of the stop lamp switch is shorted to ground.

Scheme 43

Scheme 44

The stop lamp switch signal informs the EBCM when the brake pedal is pressed.

The vehicle speed is greater than 40 km/h (25 mph).

The stop lamp switch input was active for 2 consecutive ignition cycles.

1. The EBCM disables the TCS for the duration of the ignition cycle.
2. The Traction Off indicator turns ON.
3. The ABS remains functional.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Possible causes of this DTC are the following conditions

1. The stop lamp switch circuit is shorted to voltage.
2. The stop lamp switch is misadjusted.
3. The stop lamp switch is stuck closed.
4. A brake pedal that is binding.

The number below refers to the step number on the diagnostic table.

1. 2. Test for the current state of the brake lamp switch parameter.

Scheme 45

The EBCM sources 5 volts on the stop lamp switch signal circuit when the stop lamp switch is inactive. The voltage is supplied a ground path through the stop lamp bulbs.

The ignition is ON.

The stop lamp switch input voltage is between 2.2 volts and 5.0 volts for 2 seconds.

1. The EBCM disables the TCS for the duration of the ignition cycle.
2. The Traction Off indicator turns ON.
3. The ABS remains functional.

1. The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
2. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Possible causes of this DTC are the following conditions

1. A signal circuit of the stop lamp switch is open.
2. The stop lamp switch is misadjusted.
3. Verify proper stop lamp switch operation using the data list of the scan tool. As the brake is applied, the data list displays the stop lamp switch ON within 2.54 cm (1 in) of travel.
4. All brake lamps are open.
5. All brake lamp grounds are open.
6. Circuit has a wiring problem, terminal corrosion, or poor connections.
7. Loose or corroded EBCM ground or PCM ground.
8. An internal EBCM problem.

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

3. This DTC detects an open stop lamp switch signal circuit from the stop lamp side of the splice pack to the EBCM.

4. The EBCM sources 5 volts on the stop lamp switch signal circuit. This small voltage has a ground path through the stop lamp bulbs. This DTC sets if the path to ground is open.

Scheme 46

Scheme 47

1. Perform the «DIAGNOSTIC SYSTEM CHECK - ABS»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control module(s) can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to ABS «DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the antilock brake system. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Inspect the master cylinder reservoir for the proper brake fluid level.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «ABS INDICATOR ALWAYS ON»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system)
2. «ABS INDICATOR INOPERATIVE»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system)
3. «LOW TRACTION INDICATOR ALWAYS ON»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system)
4. «LOW TRACTION INDICATOR INOPERATIVE»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system)
5. «TRACTION OFF INDICATOR ALWAYS ON»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system)
6. «TRACTION OFF INDICATOR INOPERATIVE»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system)

The instrument cluster controls the operation of the ABS indicator. The EBCM reports the desired status of the ABS indicator via serial data messages.

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

3. Use the scan tool to check the normal state of the ABS indicator control circuit.

4. Ensures that the instrument panel cluster (IPC) can operate the ABS indicator.

Scheme 48

The instrument cluster controls the operation of the ABS indicator. The EBCM reports the desired status of the ABS indicator via serial data messages.

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

3. Use the scan tool to check the normal state of the ABS indicator control circuit.

4. Ensures that the instrument panel cluster (IPC) can operate the ABS indicator.

Scheme 49

The Low Traction indicator is controlled by the instrument cluster via serial data messages from the EBCM. When the ABS or TCS is active for 0.5 seconds, the EBCM commands the instrument cluster to turn ON the Low Traction indicator.

The Low Traction indicator will also turn ON during the instrument cluster bulb check. When the ignition switch is turned to ON, the Low Traction indicator will turn ON for approximately 3 seconds and then turn OFF.

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

1. 2. Use the scan tool to check the normal state of the Low Traction indicator control.
2. 3. Ensures that the instrument cluster can operate the Low Traction indicator.

Scheme 50

The Low Traction indicator is controlled by the instrument cluster via serial data messages from the EBCM. When the ABS or TCS is active for 0.5 seconds, the EBCM commands the instrument cluster to turn ON the Low Traction indicator.

The Low Traction indicator will also turn ON during the instrument cluster bulb check. When the ignition switch is turned to ON, the Low Traction indicator will turn ON for approximately 3 seconds and then turn OFF.

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

1. 2. Use the scan tool to check the normal state of the Low Traction indicator control.
2. 3. Ensures that the instrument cluster can operate the Low Traction indicator.

Scheme 51

The Traction Off indicator is controlled by the instrument cluster via serial data messages from the EBCM. When the body control module sees the traction control switch input grounded through the momentary traction control switch, it sends a serial data message to the EBCM that tells the EBCM that the traction control switch has been pressed. The EBCM then disables traction control and sends a serial data message to the instrument cluster to turn the Traction Off indicator ON. Each time the ignition is cycled from OFF to ON, the traction control system is enabled.

The following conditions will cause the Traction Off indicator to illuminate

1. The EBCM has disabled the TCS due to a DTC.
2. The driver manually disabling the TCS via the traction control switch.
3. The instrument cluster bulb check. When the ignition switch is turned to ON, the Traction Off indicator will turn on for approximately 3 seconds and then turn OFF.

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

1. 2. Use the scan tool to check the normal state of the Traction Off indicator control.
2. 3. Ensures that the instrument cluster can operate the Traction Off indicator.

Scheme 52

The Traction Off indicator is controlled by the instrument cluster via serial data messages from the EBCM. When the body control module sees the traction control switch input grounded through the momentary traction control switch, it sends a serial data message to the EBCM that tells the EBCM that the traction control switch has been pressed. The EBCM then disables traction control and sends a serial data message to the instrument cluster to turn the Traction Off indicator ON. Each time the ignition is cycled from OFF to ON, the traction control system is enabled.

The following conditions will cause the Traction Off indicator to illuminate

1. The EBCM has disabled the TCS due to a DTC.
2. The driver manually disabling the TCS via the traction control switch.
3. The instrument cluster bulb check. When the ignition switch is turned to ON, the Traction Off indicator will turn on for approximately 3 seconds and then turn OFF.

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

1. 2. Use the scan tool to check the normal state of the Traction Off indicator control.
2. 3. Ensures that the instrument cluster can operate the Traction Off indicator.

Scheme 53

Scheme 54

Bleeding the ABS System

Note. Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Cautions and Notices.

Perform a manual or pressure bleeding procedure. Refer to PRESSURE BLEEDING . . If the desired brake pedal height results are not achieved, perform the automated bleed procedure below.

The procedure cycles the system valves and runs the pump in order to purge the air from the secondary circuits normally closed off during normal base brake operation and bleeding. The automated bleed procedure is recommended when air ingestion is suspected in the secondary circuits, or when the BPMV has been replaced.

Automated Bleed Procedure

Note. The Auto Bleed Procedure may be terminated at any time during the process by pressing the EXIT button. No further Scan Tool prompts pertaining to the Auto Bleed procedure will be given. After exiting the bleed procedure, relieve bleed pressure and disconnect bleed equipment per manufacturers instructions. Failure to properly relieve pressure may result in spilled brake fluid causing damage to components and painted surfaces.

1. Raise the vehicle on a suitable support. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
2. Remove all four tire and wheel assemblies. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tires and Wheels.
3. Inspect the brake system for leaks and visual damage. Refer to «BRAKE FLUID LOSS»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__brake-fluid-loss) or «SYMPTOMS -- HYDRAULIC BRAKES»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__symptoms-hydraulic-brakes) . Repair or replace as needed.
4. Inspect the battery state of charge. Refer to BATTERY INSPECTION/TEST in Battery.
5. Install a scan tool.
6. Turn ON the ignition, with the engine OFF.
7. With the scan tool, establish communications with the EBCM. Select Special Functions. Select Automated Bleed from the Special Functions menu.
8. Bleed the base brake system. Refer to «MANUAL BLEEDING»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__manual-bleeding) or «PRESSURE BLEEDING»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__pressure-bleeding) in Disc & Drum.
9. Follow the scan tool directions until the desired brake pedal height is achieved.
10. If the bleed procedure is aborted, a malfunction exists. Perform the following steps before resuming the bleed procedure: If a DTC is detected, refer to «DIAGNOSTIC TROUBLE CODE (DTC) LIST»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system__diagnostic-trouble-code-dtc-list) and diagnose the appropriate DTC. If the brake pedal feels spongy, perform the conventional brake bleed procedure again. Refer to «MANUAL BLEEDING»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__manual-bleeding) or «PRESSURE BLEEDING»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__pressure-bleeding) in Disc & Drum.
11. When the desired pedal height is achieved, press the brake pedal in order to inspect for firmness.
12. Remove the scan tool.
13. Install the tire and wheel assemblies. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tires and Wheels.
14. Inspect the brake fluid level. Refer to «MASTER CYLINDER RESERVOIR FILLING»(/buick/century/vi-1997-2005/remont/mechanical-hydraulic/#disc-brakes-drum-brakes__master-cylinder-reservoir-filling) .
15. Road test the vehicle while inspecting that the pedal remains high and firm.

Removal Procedure

Note. Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Cautions and Notices.

Note. To prevent equipment damage, never connect or disconnect the wiring harness connection from the EBCM with the ignition switch in the ON position.

Scheme 55

Scheme 56

1. Turn the ignition switch to the OFF position.
2. Remove the fuel injector sight shield (3.8 L engine only). Refer to FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L36) or FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L67) .
3. Remove the front fender upper diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
4. Disconnect the accelerator and cruise control cable from the accelerator control cable bracket.
5. Disconnect the cruise control module from the left strut tower. It is not necessary to remove the cable from the module. Refer to CRUISE CONTROL MODULE REPLACEMENT In Cruise Control. Position the module and cables aside.
6. Remove the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T. .
7. Disengage the red locking tab (1) from connector lock tab.
8. Push down lock tab and then move sliding connector cover (2) to the open position.
9. Disconnect the EBCM harness connector.
10. Remove any dirt/debris from the assembly.
11. Remove the four EBCM to BPMV retainers. IMPORTANT: Do not pry apart using a tool. Be careful not to damage BPMV surface. IMPORTANT: Care must be taken not to damage the solenoid valves when the EBCM is removed from the BPMV.
12. Separate the EBCM from the BPMV by gently pulling apart until separated.

Scheme 57

Scheme 58

1. Install the EBCM to the BPMV. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the four retainers that attach the EBCM to BPMV. Tighten Tighten the retainers to 5 N.m (44 lb in).
3. Connect the EBCM harness connector.
4. Push down lock tab (1) and then move sliding connector cover (2) back in the home position to lock.
5. Reengage the red locking tab (1) to the connected lock tab.
6. Install the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T. .
7. Reposition the module and cables. Connect the cruise control module to the left strut tower. Refer to CRUISE CONTROL MODULE REPLACEMENT in Cruise Control.
8. Connect the accelerator and cruise control cable to the accelerator control cable bracket.
9. Install the front fender upper diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
10. Install the fuel injector sight shield (3.8 L engine only). Refer to FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L36) or FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L67) .
11. Turn the ignition switch to the RUN position, do not start engine.
12. Perform the «DIAGNOSTIC SYSTEM CHECK - ABS»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

Note. Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Cautions and Notices.

Scheme 59

Scheme 60

Scheme 61

Scheme 62

Scheme 63

1. Turn the ignition switch to the OFF position.
2. Remove the attaching bolts for the cruise control module.
3. Swing the cruise control module off to the side.
4. Disengage the red locking tab from the connector (1).
5. Push down lock tab (1) and then move sliding connector cover (2) to the open position.
6. Disconnect the EBCM harness connector. IMPORTANT: Note the locations of the brake pipes in order to aid in installation.
7. Disconnect the wheel cylinder brake pipes (1) from the BPMV (2).
8. Swing the 4 wheel cylinder brakes pipes out of the way only after covering the open pipes to avoid dripping or being contaminated.
9. Disconnect the master cylinder brake pipes (2) from the BPMV (4).
10. It is not necessary to remove the brake pipes (2) from the master cylinder (1).
11. Swing the 2 master cylinder brake pipes out of the way only after covering the open pipes to avoid dripping or being contaminated.
12. Remove the 2 BPMV mounting bracket nuts (3) and 1 bolt located near the bottom and 1 nut (1) located at the top of the BPMV mounting bracket (4) to the strut tower.
13. Disconnect the ground strap between the EBCM assembly and the chassis.
14. Remove the BPMV mounting bracket (4) and EBCM assembly (2) from the vehicle. NOTE: When removing the brake pressure modulator valve, protect the vehicle exterior from possible brake fluid spillage. Brake fluid can cause damage to painted surfaces.
15. Remove the 4 bolts (3) that connect the BPMV (1) to the mounting bracket (2).
16. Remove EBCM if replacing the BPMV only. Refer to «ELECTRONIC BRAKE CONTROL MODULE (EBCM) REPLACEMENT»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

Scheme 64

Scheme 65

Scheme 66

Scheme 67

Scheme 68

1. Install EBCM onto the BPMV (1) if replacing the BPMV only. Refer to «ELECTRONIC BRAKE CONTROL MODULE (EBCM) REPLACEMENT»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .
2. Install BPMV and EBCM as an assembly (1) to the mounting bracket (2). NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the 4 bolts (3) that connects the BPMV assembly (1) to the mounting bracket (2). Tighten Tighten the 4 bolts (3) that connect the BPMV (1) to the mounting bracket (2) to 10 N.m (89 lb in).
4. Install the BPMV bracket (4) to the strut tower.
5. Install the 1 bolt and 3 nuts that attach the BPMV mounting bracket (4) to the strut tower. Tighten Tighten the lower 2 BPMV mounting bracket nuts (3) and bolt to 10 N.m (89 lb in). Tighten the top nut (1) for BPMV mounting bracket (4) to strut tower to 3 N.m (27 lb in). CAUTION: Make sure brake pipes are correctly connected to brake pressure modulator valve. If brake pipes are switched by mistake, wheel lockup will occur and personal injury may result. The only two ways this condition can be detected are by using a Scan Tool or by doing an Antilock stop. IMPORTANT: If a new BPMV is being installed, remove the shipping plugs from the valve openings during the next few steps when ready. Install the master cylinder brake pipes (2) into the BPMV (4). Tighten Tighten the master cylinder brake pipe fittings to 24 N.m (18 lb ft). Install the wheel cylinder brake pipes (1) on the BPMV (2). Tighten Tighten all 4 wheel cylinder brake pipe fittings to 24 N.m (18 lb ft). Re-connect the ground strap between the EBCM assembly and the chassis. Connect the EBCM harness connector. Push down lock tab (1) and then move sliding connector cover (2) back in home position to lock. Insert red locking tab back in place. Reinstall the cruise control module. When all procedures have been completed, the automated ABS bleed procedure is required. Refer to «ABS AUTOMATED BLEED PROCEDURE»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

Note. Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Cautions and Notices.

Scheme 69

1. Turn the Ignition switch to the OFF position.
2. Remove the two BPMV mounting bracket nuts (3) and one bolt located near the bottom and one nut (1) located at the top of the BPMV mounting bracket (4) to the strut tower.
3. Disconnect the ground strap between the EBCM assembly and the chassis.
4. Remove the BPMV mounting bracket (4) from the vehicle.
5. Remove BPMV and EBCM assembly (2) from the BPMV mounting bracket (4).

Scheme 70

1. Install the BPMV and EBCM assembly (2) to the BPMV mounting bracket (4).
2. Install the BPMV bracket (4) to the strut tower. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the one bolt and three nuts that attach the BPMV mounting bracket (4) to the strut tower. Tighten Tighten the lower two BPMV mounting bracket nuts (3) and bolt to 10 N.m (89 lb. in.). Tighten the top nut (1) for BPMV mounting bracket (4) to strut tower to 3 N.m (27 lb. in.).
4. Reconnect the ground strap between the EBCM assembly and the chassis.
5. Turn the ignition switch to the RUN position, engine off.
6. Perform the «DIAGNOSTIC SYSTEM CHECK - ABS»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

If a speed sensor or a ring needs replacement, replace the entire hub and bearing assembly. Do not service the harness pigtail individually because the harness pigtail is part of the sensor. Refer to WHEEL BEARING/HUB REPLACEMENT - FRONT in Front Suspension.

Scheme 71

Scheme 72

1. Raise and support the vehicle on a suitable hoist. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
2. Remove the front tire and wheel assembly. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tire and Wheels.
3. Disconnect the front wheel speed sensor jumper harness electrical connector (1).
4. Remove the hub and bearing assembly (2). Refer to WHEEL BEARING/HUB REPLACEMENT - FRONT in Front Suspension.

Scheme 73

Scheme 74

1. Install the hub and bearing assembly (2) to the vehicle. Refer to WHEEL BEARING/HUB REPLACEMENT - FRONT in Front Suspension.
2. Install the front wheel speed sensor jumper harness electrical connector (1).
3. Install the wheel and tire assembly. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tires and Wheels.
4. Lower the vehicle.
5. Turn the ignition switch to the ON position with the engine off.
6. Perform the «DIAGNOSTIC SYSTEM CHECK - ABS»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

If a speed sensor or a ring needs replacement, replace the entire hub and bearing assembly. Refer to Wheel Bearing/Hub Replacement - Rear (Disc Brakes) or Wheel Bearing/Hub Replacement - Rear (Drum Brakes) in Rear.

Scheme 75

Scheme 76

1. Raise and support the vehicle on a suitable hoist. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
2. Remove the rear tire and wheel assembly. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tires and Wheels.
3. Disconnect the electrical connector from the rear wheel speed sensor.
4. Remove the hub and bearing assembly (1). Refer to Wheel Bearing/Hub Replacement - Rear (Disc Brakes) or Wheel Bearing/Hub Replacement - Rear (Drum Brakes) in Rear.

Scheme 77

Scheme 78

1. Install the hub and bearing assembly (1) to the vehicle. Refer to Wheel Bearing/Hub Replacement - Rear (Disc Brakes) or Wheel Bearing/Hub Replacement - Rear (Drum Brakes) in Rear.
2. Connect the electrical connector to the rear wheel speed sensor.
3. Install the wheel and tire assembly. Refer to TIRE AND WHEEL REMOVAL AND INSTALLATION in Tires and Wheels.
4. Lower the vehicle.
5. Turn the ignition switch to the ON position, with the engine off.
6. Perform the «DIAGNOSTIC SYSTEM CHECK - ABS»(/buick/century/vi-1997-2005/remont/anti-locktraction-control/#antilock-brake-system) .

Scheme 79

1. Depress the retainers on each side of the traction control/heated seat switch using a small flat-bladed tool.
2. Lift the traction control/heated seat switch from the front of the floor console trim plate.
3. Disconnect the electrical connector from the traction control switch.
4. Disconnect the electrical connectors from the heater seat switches.

Scheme 80

1. Connect the electrical connector to the traction control switch.
2. Connect the electrical connectors to the heater seat switches.
3. Position the traction control/heated seat switch to the front floor console trim plate.
4. Install the traction control/heated seat switch into the console trim plate pressing in until the retainers are fully seated.

Scheme 81

Scheme 82

This vehicle is equipped with the DBC7 antilock braking system.

The vehicle is equipped with the following braking systems

1. Antilock Brake System (ABS)
2. Dynamic Rear Proportioning (DRP)
3. Traction Control System (TCS) (w/NW9)
4. Traction Control System (TCS) (w/NW7)

The following components are involved in the operation of the above systems

1. Electronic Brake Control Module (EBCM) - The EBCM controls the system functions and detects failures. The EBCM contains the following components: System Relay - The system relay is energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the solenoid valves and pump motor. Vent Tube - The vent tube, located in the EBCM connector, is an opening to the internal cavity of the EBCM. It allows ventilation of the EBCM internals.
2. Brake Pressure Modulator Valve (BPMV) - The BPMV contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The BPMV uses a 4 circuit configuration with a diagonal split. The BPMV directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other. The BPMV contains the following components: The Pump Motor One Inlet Valve per wheel One Outlet Valve per wheel One TCS Valve per drive wheel (w/NW9)
3. Wheel Speed Sensors (WSS) - As the wheel spins, the wheel speed sensor produces an AC signal. The EBCM uses this AC signal to calculate wheel speed. The wheel speed sensors are replaceable only as part of the wheel hub and bearing assemblies.
4. Traction Control Switch (w/NW9) - The TCS is manually disabled or enabled using the traction control switch.
5. Stop Lamp Switch - The EBCM uses the stoplamp switch as an indication that the brake pedal is applied.

Initialization Sequence

The EBCM performs 1 initialization test each ignition cycle. The initialization of the EBCM occurs when 1 set of the following conditions occur

Both of the following conditions occur

1. The EBCM detects that there is a minimum of 500 RPM from the PCM via a serial data message.
2. The stop lamp switch is not applied.

OR

Both of the following conditions occur

1. The vehicle speed is greater than 16 km/h (10 mph).
2. The stop lamp switch is applied.

The initialization sequence may also be commanded with a scan tool.

The initialization sequence cycles each solenoid valve and the pump motor, as well as the necessary relays, for approximately 1.5 seconds to check component operation. The EBCM sets a DTC if any error is detected. The initialization sequence may be heard and felt while it is taking place, and is considered part of normal system operation.

The EBCM defines a drive cycle as the completion of the initialization sequence.

When wheel slip is detected during a brake application, the ABS enters antilock mode. During antilock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decreases, hold, or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking. During antilock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the EBCM responds to wheel speed sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present only during antilock braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle rapidly. During antilock braking on dry pavement, intermittent chirping noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal during antilock operation.

Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability.

Pressure Hold

The EBCM closes the inlet valve and keeps the outlet valve closed in order to isolate the system when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decreases.

Pressure Decrease

The EBCM decreases the pressure to individual wheels during a deceleration when wheel slip occurs. The inlet valve is closed and the outlet valve is opened. The excess fluid is stored in the accumulator until the return pump can return the fluid to the master cylinder.

Pressure Increase

The EBCM increases the pressure to individual wheels during a deceleration in order to reduce the speed of the wheel. The inlet valve is opened and the outlet valve is closed. The increased pressure is delivered from the master cylinder.

Traction Control System (TCS) (NW9)

When drive wheel slip is noted while the brake is not applied, the EBCM will enter traction control mode.

First, the EBCM requests the PCM to reduce the amount of torque to the drive wheels via the requested torque signal circuit. The PCM reduces torque to the drive wheels by retarding spark timing and turning off fuel injectors. The PCM reports the amount torque delivered to the drive wheels via the delivered torque signal circuit.

If the engine torque reduction does not eliminate drive wheel slip, the EBCM will actively apply the drive wheel brakes. During traction control braking, hydraulic pressure in each drive wheel circuit is controlled to prevent the drive wheels from slipping. The master cylinder isolation valve closes in order to isolate the master cylinder from the rest of the hydraulic system. The prime valve then opens in order to allow the pump to accumulate brake fluid in order to build hydraulic pressure for braking. The drive wheel inlet and outlet solenoid valves then open and close in order to perform the following functions

1. Pressure hold
2. Pressure increase
3. Pressure decrease

Traction Control System (TCS) (NW7)

When drive wheel slip is noted while the brake is not applied, the EBCM will enter traction control mode.

The EBCM requests the PCM to reduce the amount of torque to the drive wheels via serial data messages. The PCM reduces torque to the drive wheels by retarding spark timing and turning off fuel injectors. The PCM reports the amount torque delivered to the drive wheels via serial data messages.

ABS Indicator

The IPC illuminates the ABS indicator when the following occurs

1. The electronic brake control module (EBCM) detects a malfunction with the antilock brake system. The IPC receives a class 2 message from the EBCM requesting illumination.
2. The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
3. The IPC detects a loss of class 2 communications with the EBCM.

TRAC OFF

The IPC illuminates the TRAC OFF indicator when the following occurs

1. The electronic brake control module (EBCM) inhibits the traction control system due to a malfunction in the traction control system. The IPC receives a class 2 message from the EBCM requesting illumination.
2. The body control module (BCM) detects that the traction control switch has been pressed (signal circuit is low). The BCM sends a class 2 message to the EBCM in order to disable traction control. The IPC receives a class 2 message from the EBCM requesting illumination. The IPC sends a class 2 message to the BCM in order to activate an audible warning.

LOW TRAC

The IPC illuminates the LOW TRAC indicator when the electronic brake control module (EBCM) detects a traction control event. The IPC receives a class 2 message from the EBCM requesting illumination.

Scheme 83

Scheme 84

See also:
• PRESSURE BLEEDING
• LIFTING AND JACKING THE VEHICLE
• BRAKE FLUID LOSS
• SYMPTOMS -- HYDRAULIC BRAKES
• MANUAL BLEEDING
• MASTER CYLINDER RESERVOIR FILLING
• AIR CLEANER INTAKE DUCT
• FASTENER NOTICE
• DIAGNOSTIC SYSTEM CHECK - ABS
• DIAGNOSTIC TROUBLE CODE (DTC) LIST