Anti-Lock Brake System & Traction Control Buick LeSabre VII

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DESCRIPTION

The Teves 4-wheel Anti-Lock Brake System (ABS) and Traction Control System (TCS) are designed to prevent wheel lock-up during heavy braking and acceleration slip/traction at speeds less than 25 MPH. The ABS allows driver to maintain steering control while stopping vehicle in shortest distance possible, while TCS uses ABS components to prevent wheels from spinning excessively during acceleration. Major components include the following: pump motor, Pressure Modulator Valve (PMV) assembly, fluid reservoir with integral filter, wheel speed sensors (4), fluid level sensor, Electronic Brake Control Module (EBCM) or Electronic Brake and Traction Control Module (EBTCM), brake booster/master cylinder assembly, and BRAKE and ANTI-LOCK warning lights.

Note. For more information on brake system, see BRAKE SYSTEM article in BRAKES.

During normal driving and braking operations, ABS acts like a conventional braking system. Each wheel sensor constantly sends an AC voltage signal to EBCM/EBTCM, which then translates this information into wheel rotation or wheel speed.

When EBCM/EBTCM determines wheels are about to lock-up, it activates Pressure Modulator Valve (PMV) to increase or decrease hydraulic pressure to each wheel. A slight pulsation should be felt through brake pedal.

BRAKE, ANTI-LOCK and TRACTION OFF warning lights (if equipped) should come on when ignition switch is turned and vehicle is started. If any instrument panel warning light stays on longer than approximately 5 seconds after vehicle is started, system malfunction is indicated. See DIAGNOSIS & TESTING .

MANUAL BLEEDING

Note. Ensure brake fluid reservoir cap is properly installed to prevent brake fluid from splashing from master cylinder reservoir during bleeding procedure.

Master Cylinder

1. With engine off, pump brake pedal several times to deplete vacuum reserve in brake booster. Remove brake fluid reservoir cap and add clean DOT 3 brake fluid (if necessary) to fill reservoir to full mark. Replace reservoir cap.
2. Loosen forward (secondary) brakeline fitting at master cylinder. Allow fluid to flow from fitting port while maintaining correct fluid level. Tighten forward brakeline fitting. Slowly depress brake pedal once and hold. Loosen forward fitting, and allow air to be bled out. Tighten fitting. Slowly release brake pedal.
3. Wait 15 seconds. Repeat step 2) (if necessary) until all air is purged. Tighten brakeline fitting to specification. See «TORQUE»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control) SPECIFICATIONS. Repeat procedure for master cylinder rearward (primary) brakeline fitting.

Brakelines

1. Raise and support vehicle. Remove bleeder cap from right rear wheel bleeder valve. Attach hose to bleeder valve. Submerge other end of hose in container of clean brake fluid.
2. Using Brake Bleeder Wrench (J-21472 or J-28434), loosen bleeder valve while an assistant depresses brake pedal to its full travel. Hold brake pedal in depressed position, and close bleeder valve. NOTE: Rapid pumping of brake pedal causes master cylinder secondary piston to move into a position that makes bleeding system difficult.
3. Slowly release brake pedal. Wait 15 seconds, and then repeat operation until no air bubbles emerge from submerged end of hose. Repeat procedure for remaining wheels in following sequence: left rear, right front and then left front. Tighten bleeder valves to specification. See «TORQUE SPECIFICATIONS»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control) .

PRESSURE BLEEDING

Note. Pressure bleeding equipment must be diaphragm type, with rubber diaphragm between air supply and brake fluid to prevent contamination of brake system.

1. Clean reservoir cap area. Fill master cylinder to full mark. Install Brake Bleeder Adapter (J-35589) on master cylinder. Attach Pressure Bleeder (J-29532).
2. Raise and support vehicle. Remove dust cap from right rear wheel bleeder valve. Attach hose to right rear bleeder valve. Submerge other end of hose in container of clean brake fluid.
3. Open valve on bleeder tank to pressurize system. Maintain system pressure of 20-25 psi (1.4-1.8 kg/cm 2 ). Using appropriate Brake Bleeder Wrench (J-21472 or J-28434), open bleeder valve until no air bubbles emerge from submerged end of hose.
4. Repeat procedure for remaining wheels in following sequence: left rear, right front and then left front. After procedure is complete, close pressure bleeder tank valve, and remove adapter. Fill fluid level to full mark. Tighten bleeder valves to specification. See «TORQUE SPECIFICATIONS»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control) .

AIR BAG SYSTEM

Observe the following precautions when working with air bag systems

1. Before performing any repairs, disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM.»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control)
2. After air bag system is disabled, wait 2 MINUTES before working on vehicle, as energy reserve module retains sufficient voltage to deploy air bag.
3. Handle air bag sensor carefully to avoid injury. DO NOT strike or jar sensor, as air bag deployment or improper operation of air bag system could result. Replace sensor if dropped from a height of 2 feet or more.
4. Sensors and mounting bracket bolts must be carefully torqued to ensure correct operation. DO NOT activate air bag system if any sensor is not rigidly attached to vehicle.
5. When carrying a live inflator module, ensure bag and trim cover are pointed away from body. This reduces chance of injury in case of accidental air bag deployment.
6. When placing a live inflator module on a bench or other surface, always face bag and trim cover up, away from surface. NEVER carry any air bag system component by wires or connector.

Note. To diagnose ABS/TCS system, manufacturer recommends using Tech 1 Scan Tester (94-00101-A) with 1988-95 Brake Cartridge. Some diagnostic procedures will require EBCM/EBTCM Pinout Box (J-38716) and High-Impedance Digital Multimeter (J-39200) or equivalent. When using Tech 1 for diagnostics, ABS system is disabled by EBCM. ANTI-LOCK indicator will come on indicating only normal power assisted braking is available. After diagnostics have been completed using Tech 1, disconnect Tech 1 from Data Link Connector (DLC) and turn ignition off for at least 10 seconds before road testing. This procedure is done to reset EBCM.

The EBCM/EBTCM has self-diagnostic capability, which can detect system failures. Fault codes stored by EBCM/EBTCM can be displayed using Tech 1 scan tester. There are no provisions for flash code diagnostics.

Begin ABS/TCS diagnosis with PRE-DIAGNOSTIC INSPECTION procedure. If failures are found during pre-diagnostic inspection, perform necessary repairs, and proceed with ABS/TCS FUNCTIONAL CHECK. (Scheme 5)

If no failures are found during pre-diagnostic inspection, go to ABS/TCS FUNCTIONAL CHECK. (Scheme 5) The ABS/TCS FUNCTIONAL CHECK will either indicate ABS/TCS is functioning properly or direct technician to various diagnostic procedures such as diagnostic charts, symptom diagnosis or BRAKE warning light diagnosis.

PRE-DIAGNOSTIC INSPECTION

Before diagnosing ABS/TCS, perform a comprehensive visual inspection of system as follows.

1. Check ABS/TCS wiring harness connectors for looseness. Check harness routing; pay particular attention to wheel speed sensor wiring harness routing.
2. Check fuses No. 1D, 5B and 6B in instrument panel fuse block. Check fuses No. 1 and 2 in underhood fuse block.
3. Check brake fluid level in master cylinder reservoir.
4. Check brake fluid level in Pressure Modulator Valve (PMV) assembly reservoir.
5. Ensure parking brake is fully released.
6. Ensure parking brake switch is functioning properly.
7. Always perform ABS/TCS system functional check before using DIAGNOSTIC CODE CHARTS. (Scheme 5)

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ENTERING ON-BOARD DIAGNOSTICS

Note. Intermittent history codes do not illuminate Amber ANTI-LOCK warning light. DO NOT use DIAGNOSTIC TROUBLE CODE table for intermittent problems. See INTERMITTENTS & POOR CONNECTIONS under DIAGNOSIS & TESTING.

1. Connect Tech 1 scan tester to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Follow scan tester manufacturer's instructions to retrieve stored fault codes. If no codes are present, identify symptom and perform appropriate SYMPTOM DIAGNOSIS CHART. See «SYMPTOM DIAGNOSIS»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control__symptom-diagnosis) .
2. If code is present, perform appropriate DIAGNOSTIC CODE CHART. See DIAGNOSTIC TROUBLE CODE (DTC) table. If multiple codes are displayed, diagnose codes in the order displayed by Tech 1 scan tester.
3. After repair(s) is complete, follow scan tester manufacturer's instructions to clear all stored fault codes.

DIAGNOSTIC TROUBLE CODE (DTC)

SYMPTOM DIAGNOSIS

SYMPTOM DIAGNOSIS

INTERMITTENTS & POOR CONNECTIONS

There are 2 types of trouble codes: current and history codes. Current codes indicate existing failures, while history codes indicate intermittent failures. Diagnostic charts can be used to identify intermittent problems in ABS electrical components, but fault must be present during testing in order to correctly locate problem.

Most intermittent problems are caused by faulty electrical connections or wiring. When an intermittent failure is encountered, visually inspect suspect circuits for the following conditions.

1. Check for poor mating of connector halves or terminals not fully seated in connector body (backed out).
2. Check for improperly formed or damaged terminals. All connector terminals in a problem circuit should be carefully reformed to increase contact tension.
3. Check for poor terminal-to-wire connection. Terminal and wire need to be removed from connector body for inspection.

If visual inspection does not help locate intermittent problem, use ABS self-diagnostic system to identify suspect circuit. Before using codes to diagnose intermittent failure, perform the following steps

1. Display and then clear ABS trouble codes in Electronic Brake Computer Module (EBCM).
2. Test drive vehicle, and attempt to duplicate conditions causing problem or complaint. Stop vehicle, and record any codes set.

The following conditions may cause intermittent operation of ANTI-LOCK warning light.

1. Low Or Intermittent Voltage At EBCM/EBTCM
2. Low Brake Fluid Or Low Fluid Pressure
3. Interruption Of Power To EBCM/EBTCM Or Hydraulic Pump Motor Circuits (Main Relay, Pump Motor Relay, Fuses And Related Wiring)

Circuit Description

When ignition switch is first turned to RUN position, EBCM/EBTCM goes through a self-test, which lasts 2-4 seconds. During self-test, EBCM/EBTCM grounds terminal No. 52, causing Amber ANTI-LOCK warning light to illuminate.

When low fluid condition exists, EBCM/EBTCM turns on Amber ANTI-LOCK warning light, but does not set Diagnostic Trouble Code (DTC). Low fluid level condition usually lights Red BRAKE warning light since master cylinder supplies brake fluid to Pressure Modulator Valve (PMV) reservoir. Restrictions or air in hose could cause a low fluid condition in PMV reservoir without lighting Red BRAKE warning light.

Diagnostic Aids

Check for open in circuit No. 641 (Brown wire), circuit No. 800 (Tan wire), circuit No. 849 (Pink wire), circuit No. 853 (Light Blue/Black wire) and circuit No. 1050 (Black or Black/White wire). Check for low brake fluid level, open in PMV fluid level switch or wrong scan tester adapter. Check for short to ground in circuit No. 641 (Brown wire), circuit No. 800 (Tan wire) and circuit No. 852 (White wire).

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When ignition switch is first turned to RUN position, EBCM/EBTCM goes through a self-test, which lasts 2-4 seconds. During self-test, EBCM/EBTCM grounds terminal No. 52, causing Amber ANTI-LOCK warning light to illuminate.

EBCM/EBTCM also grounds terminal No. 34, energizing main relay and removing warning light ground path provided through anti-lock diode and main relay contacts. When self-test is completed and no faults are detected, EBCM/EBTCM removes ground at terminal No. 52, turning off warning light. Main relay remains energized.

When EBCM/EBTCM detects a fault, it grounds terminal No. 52, causing Amber ANTI-LOCK warning light to illuminate. EBCM/EBTCM will also de-energize main relay, creating a redundant ground path. If EBCM/EBTCM is disabled for any reason, main relay will be de-energized. This provides ANTI-LOCK warning light ground path through anti-lock diode and main relay contacts, causing warning light to illuminate with no DTCs being set.

Check for open in circuit No. 852 (White wire), circuit No. 1050 (Black or Black/White wire) and circuit No. 1633 (Red wire). Check for open in warning light bulb. Check for short to voltage on circuit No. 852 (White wire). Check for open or shorted anti-lock diode. Check for main relay failure. Check for short to ground in circuit No. 1632 (Pink wire).

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When ignition switch is first turned to RUN position, EBTCM goes through a self-test, which lasts 2-4 seconds. During self-test, EBTCM grounds ANTI-LOCK and TRACTION OFF warning lights.

Traction control switch is located either on instrument panel center trim plate or driver's front door trim panel. Switch allows driver to select traction control mode (on/off). When traction control system is turned off, TRACTION OFF warning light comes on.

EBTCM monitors transaxle temperature through information provided by Powertrain Control Module (PCM). When transaxle becomes hot, about 320°F (160°C), EBTCM disables traction control system and turns on TRACTION OFF warning light. This allows brakes and transaxle to cool down.

When transaxle cools to 300°F (149°C), EBTCM keeps TRACTION OFF warning light on and disables traction control for an additional 3-5 minutes to allow sufficient cooling.

Check for short to ground in circuit No. 1571 (Brown/White wire) and circuit No. 1572 (Purple/White wire). Check for faulty traction control switch or EBTCM.

Note. With traction control (if equipped), any symptom lighting ANTI-LOCK warning light will also light TRACTION OFF warning light. When both warning indicators are on, perform ANTI-LOCK warning light diagnosis if no DTC is set.

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When ignition switch is first turned to RUN position, EBTCM goes through a self-test, which lasts 2-4 seconds. During self-test, EBTCM commands TRACTION OFF indicator warning light on. Powertrain Control Module (PCM) can also command EBTCM to set a Code 75 which will illuminate TRACTION OFF indicator.

Traction control switch is located either on instrument panel center trim plate or driver's front door trim panel. Switch allows driver to select traction control mode (on/off). When traction control system is turned off, TRACTION OFF warning light comes on.

EBTCM monitors transaxle temperature through information provided by PCM. When transaxle becomes hot, about 320°F (160°C), EBTCM disables traction control system and turns on TRACTION OFF warning light. This allows brakes and transaxle to cool down.

When transaxle cools to 300°F (149°C), EBTCM keeps TRACTION OFF warning light on and disables traction control for an additional 3-5 minutes to allow sufficient cooling.

Check for short to ground in circuit No. 800 (Tan wire), circuit No. 1050 (Black or Black/White wire) and circuit No. 1571 (Brown/White wire). Check for faulty traction control switch or EBTCM.

Note. With traction control (if equipped), any symptom lighting ANTI-LOCK warning light will also light TRACTION OFF warning light. When both warning indicators are on, perform ANTI-LOCK warning light diagnosis if no DTC is set.

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EBTCM performs a self-test whenever ignition switch is first turned to RUN position. During this test, EBTCM grounds both ANTI-LOCK and TRACTION OFF indicators for about 2-4 seconds. This acts as a bulb check for the indicators.

Traction control switch is located either on instrument panel center trim plate or driver's front door trim panel. Switch allows driver to select traction control mode (on/off). When traction control system is turned off, TRACTION OFF warning light comes on.

Check for open in circuit No. 251 (Black/White wire), circuit No. 1571 (Brown/White wire) and circuit No. 1572 (Purple/White wire). Check for faulty indicator light bulb or traction control switch.

Note. With traction control (if equipped), any symptom lighting ANTI-LOCK warning light will also light TRACTION OFF warning light. When both warning indicators are on, perform ANTI-LOCK warning light diagnosis if no DTC is set.

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EBTCM enters a self-test whenever ignition switch is first turned to RUN position. During this test, EBTCM commands Instrument Panel Cluster (IPC) to turn TRACTION OFF indicator on for about 2-4 seconds. This acts as a bulb check.

Traction control switch is located in either the instrument panel center trim plate or the driver's front door trim panel. Switch allows driver to select traction control mode (on/off). When traction control system is turned off, TRACTION OFF indicator illuminates.

Check for open in circuit No. 251 (Black/White wire), circuit No. 800 (Tan wire), circuit No. 1571 (Brown/White wire) and circuit No. 1572 (Purple/White wire). Check for faulty indicator light bulb, traction control switch, IPC or IPC circuits.

Note. With traction control (if equipped), any symptom lighting ANTI-LOCK warning light will also light TRACTION OFF warning light. When both warning indicators are on, perform ANTI-LOCK warning light diagnosis if no DTC is set.

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When EBTCM is operating in traction control mode, EBTCM commands Instrument Panel Cluster (IPC) to turn TRACTION ACTIVE indicator on. This indicates traction control system is operating.

Check for faulty indicator light bulb, EBTCM or IPC.

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When EBTCM is operating in traction control mode, EBTCM commands Instrument Panel Cluster (IPC) to turn TRACTION ACTIVE indicator on. This indicates traction control system is operating. If vehicle is equipped with a digital instrument cluster (U2A), IPC will send a signal to Driver Information Center (DIC). The DIC will then display TRACTION CNTL ACTIVE when traction control is operating.

Check for faulty indicator light bulb, EBTCM or IPC.

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Traction control switch indicator is on whenever ignition is in RUN, BULB TEST or START position. Traction control switch indicator is not serviced separately from switch. If bulb is blown, switch must be replaced. Traction control switch indicator is not illuminated if an ABS or TCS failure is present.

Check for blown 1D fuse in instrument panel fuse block. Check for open in circuit No. 1572 (Purple/White wire). Check for faulty indicator light bulb or traction control switch.

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Toothed wheel generates a voltage pulse as it moves past sensor. EBCM/EBTCM uses these pulses to determine wheel speed. EBCM/EBTCM uses wheel speed sensor signal to calculate vehicle reference speeds, individual speed, acceleration value and slip value for each wheel. These values are used to determine when anti-lock or traction control (if equipped) is needed.

In order to prevent electromagnetic interference from disturbing wheel speed sensor signal, wiring from EBCM/EBTCM to each wheel speed sensor are twisted, in pairs, a minimum of 6-9 turns per foot. When servicing speed sensor wiring, ensure original wiring twists are maintained.

Test Description

EBCM/EBTCM performs 2 basic checks on wheel speed sensors: sensor continuity and sensor output. When ignition switch is first turned to RUN position, EBCM/EBTCM performs wheel speed sensor continuity check. Any condition causing lack of continuity in front wheel speed sensor circuit could result in setting of DTC 21 or 25. Conditions include the following: open or short to ground, short between 2 wheel speed sensor circuits, short in wiring harness between speed sensor and EBCM/EBTCM, or open or short to ground across wheel speed sensor coil.

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Toothed wheel generates a voltage pulse as it moves past sensor. EBCM/EBTCM uses these pulses to determine wheel speed. EBCM/EBTCM uses wheel speed sensor signal to calculate vehicle reference speeds, individual speed, acceleration value and slip value for each wheel. These values are used to determine when anti-lock or traction control (if equipped) is needed.

In order to prevent electromagnetic interference from disturbing wheel speed sensor signal, wiring from EBCM/EBTCM to each wheel speed sensor are twisted, in pairs, a minimum of 6-9 turns per foot. When servicing speed sensor wiring, maintain original wiring twists.

EBCM performs 2 basic checks on wheel speed sensors: sensor continuity and sensor output. When ignition switch is first turned to RUN position, EBCM/EBTCM performs wheel speed sensor continuity check.

Any condition causing lack of continuity in rear wheel speed sensor circuit could result in setting of DTCs 31 or 35. Conditions include the following: open or short to ground, short between 2 wheel speed sensor circuits, short in wiring harness between speed sensor and EBCM/EBTCM, or open or short to ground across wheel speed sensor coil.

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Toothed wheel generates a voltage pulse as it moves past sensor. EBCM/EBTCM uses these pulses to determine wheel speed. EBCM/EBTCM uses wheel speed sensor signal to calculate vehicle reference speeds, individual speed, acceleration value and slip value for each wheel. These values are used to determine when anti-lock or traction control (if equipped) is needed.

In order to prevent electromagnetic interference from disturbing wheel speed sensor signal, wiring from EBCM/EBTCM to each wheel speed sensor are twisted in pairs, a minimum of 6-9 turns per foot. When servicing speed sensor wiring, maintain original wiring twists.

DTC 22, 26, 33 or 36 will set if EBCM/EBTCM detects electromagnetic interference in a wheel speed sensor signal. Possible interference sources include accessory motors, wiper motors, ignition circuit and add-on or aftermarket equipment.

DTC 22, 26, 32 or 36 will set if EBCM/EBTCM determines wheel speed signal is erratic; for example, wheel speed signal indicates wheel is accelerating or decelerating faster than physically possible. An intermittent open or short to ground in a wheel speed sensor could also set DTC.

DTC 23, 27, 33 or 37 will set if EBCM/EBTCM does not sense any wheel speed signal, but determines continuity exists in speed sensor circuit. No wheel speed signal could be caused by a dislodged wheel speed sensor, missing toothed sensor ring (front) or defective hub/bearing assembly (rear).

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When ignition switch is first turned to RUN position, EBCM/EBTCM goes through a self-check, which lasts 2-4 seconds. During self-check, EBCM/EBTCM grounds terminal No. 34 to energize main relay. After self-check is completed, main relay remains energized.

With main relay energized, battery voltage is delivered to EBCM/EBTCM and Pressure Modulator Valve (PMV) during vehicle operation. Constant battery voltage allows vehicle to enter ABS mode without delay. If Amber ANTI-LOCK warning light comes on because of a system fault, main relay will be de-energized, causing ABS system to shut down.

If battery voltage is not detected at PMV or EBCM terminals No. 3, 20, and 33, DTC 45 will set when ignition switch turned to RUN position. DTC 45 will also set if EBCM detects an open or a short to ground in left inlet valve circuit.

Check for open in circuit No. 342 (Red wire), circuit No. 641 (Brown wire), circuit No. 1632 (Pink wire) and circuit No. 1633 (Red wire). Check main relay for open circuit. (Scheme 1) Check for short to ground in circuit No. 342 (Red wire), circuit No. 858 (Dark Green/Yellow wire) and circuit No. 1633 (Red wire).

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Inlet Valves

Voltage is applied to normally open inlet valves whenever main relay is energized. An inlet valve closes when EBCM/EBTCM supplies a ground path at inlet valve control terminal. EBCM/EBTCM closes an inlet valve for short periods to maintain (hold) or reduce pressure at a particular wheel.

Outlet Valves

Normally closed outlet valves operate similar to inlet valves; however, when EBCM/EBTCM grounds an outlet valve, valve opens instead of closes. EBCM/EBTCM opens an outlet valve for short periods to reduce pressure at a particular wheel.

Valves have 3 positions: pressure increase (inlet valve open, outlet valve closed), pressure hold (inlet valve closed, outlet valve closed) and pressure reduce (inlet valve closed, outlet valve open).

Test checks for proper inlet and outlet valve operation. Wheel brake operation must be checked to verify valve hydraulics are functioning. Tech 1 scan tester is used to actuate inlet and outlet valves. DTC 41, 42, 45, 46, 51, 52, 55 or 56 will set if EBCM/EBTCM detects an open or short to ground in respective inlet or outlet valve circuits.

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Voltage is applied to normally open isolation valves whenever main relay is energized. Isolation valve closes when EBCM/EBTCM supplies ground path at isolation valve control terminal. EBCM/EBTCM closes isolation valve when EBCM/EBTCM detects wheel slip in a drive wheel and vehicle speed is less than 25 MPH (40 km/h).

Isolation valves are closed only during traction control operations; valves are not used during any anti-lock or normal braking conditions. Isolation valves separate front brake hydraulic circuits from master cylinder and rear brake hydraulic circuits. Once front brake hydraulic circuits are isolated, pressure can be applied to front wheels without affecting any other brake hydraulic circuit.

DTC 44 or 48 will set if EBCM/EBTCM detects open or short to ground in respective isolation valve circuit.

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When EBCM/EBTCM grounds terminal No. 15, pump relay contacts close, applying voltage to Pressure Modulator Valve (PMV) pump motor. EBCM/EBTCM turns on pump motor during most ABS braking conditions and all traction control conditions (if equipped).

When pump motor runs during ABS braking, PMV reservoir is replenished, and fluid pressure is applied to master cylinder. Fluid pressure causes brake pedal to rise gradually. Pump motor runs until brake pedal rises sufficiently to close Torque Converter Clutch (TCC)/anti-lock brake switch.

During traction control mode, after front hydraulic brake circuits are isolated, pump motor runs to increase brake fluid pressure in these circuits. Increased brake fluid pressure is directed to slipping wheel through PMV front inlet and outlet valves. This causes brakes to be applied, reducing wheel spin at slipping wheel. Traction control is disabled as soon as brakes are manually applied.

EBCM/EBTCM monitors pump motor operation via pump motor run sensor. When pump is operating, voltage is induced into sensor coil, and EBCM/EBTCM monitors this voltage at terminals No. 31 and 49.

When EBCM/EBTCM grounds terminal No. 15, DTC 61 will set if EBCM/EBTCM determines frequency between EBCM/EBTCM terminals No. 31 and 49 is not more than 160 Hz.

EBCM/EBTCM recognizes this condition only during ABS braking requiring pump motor operation, traction control mode (if equipped) or EBCM/EBTCM self-check, which occurs when vehicle speed reaches 7 MPH (11 km/h).

DTC 61 will also set if pump motor runs constantly (i.e., EBCM/EBTCM senses proper voltage between terminals No. 31 and 49 without grounding terminal No. 15).

Check for open in circuit No. 854 (Pink wire), circuit No. 864 (Red wire), circuit No. 1150 (Black wire), circuit No. 1292 (Light Green/Black wire), circuit No. 1293 (Light Blue/Black wire) and circuit No. 1633 (Red wire). Check ABS pump relay for open circuit or engaged mode.

Check for short to ground in circuit No. 642 (Red wire), circuit No. 854 (Pink wire), circuit No. 864 (Red wire), circuit No. 1292 (Light Green/Black wire) and circuit No. 1293 (Light Blue/Black wire).

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EBCM/EBTCM monitors brake pedal position using Torque Converter Clutch (TCC)/anti-lock brake switch input. TCC/anti-lock brake switch is normally closed; switch opens when brake pedal is depressed approximately 40 percent. EBCM/EBTCM also monitors pump motor operation using a pump motor run sensor.

During most ABS braking conditions, EBCM/EBTCM turns on pump motor, replenishing Pressure Modulator Valve (PMV) reservoir and applying fluid pressure to master cylinder. This causes brake pedal to gradually rise. EBCM/EBTCM turns off pump motor when brake pedal height rises sufficiently to close TCC/anti-lock brake switch.

During ABS braking, DTC 62 will set if EBCM/EBTCM determines pump is working, but brake pedal height has not risen sufficiently to close TCC/anti-lock brake switch after 3 seconds.

DTC 62 usually indicates a hydraulic problem. Possible causes include air in brakelines or pump motor mechanical failure. Non-hydraulic causes for DTC 62 include open in circuit No. 848 (Tan wire) and circuit No. 853 (Light Blue/Black wire), or misadjusted or defective TCC/anti-lock brake switch.

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DTC 71 indicates a failure has occurred within EBCM/EBTCM. DTC 71 can occur intermittently because of electromagnetic interference. Clear DTC and test drive vehicle before replacing EBCM/EBTCM.

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EBCM/EBTCM monitors brake pedal position using brake travel switch input. Brake travel switch is normally closed; switch opens when brake pedal is depressed approximately 40 percent.

During most ABS braking conditions, EBCM/EBTCM turns on pump motor, replenishing Pressure Modulator Valve (PMV) reservoir and applying fluid pressure to master cylinder. This causes brake pedal to gradually rise. EBCM/EBTCM turns off pump motor when brake pedal height rises sufficiently to close Torque Converter Clutch (TCC)/anti-lock brake switch.

DTC 72 will set if EBCM/EBTCM detects brake travel switch circuit No. 848 (Tan wire) is shorted to ground (with brake pedal depressed).

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Pressure Modulator Valve (PMV) fluid level switch alerts EBCM/EBTCM of low brake fluid condition in PMV reservoir. Switch is located in PMV fluid reservoir and is normally closed when reservoir contains sufficient fluid. When fluid level is low, switch opens, causing EBCM/EBTCM to turn on ANTI-LOCK warning indicator.

DTC 73 will set if EBCM/EBTCM detects a short to ground in PMV fluid level switch circuit No. 848 (Tan wire), circuit No. 849 (Pink wire), circuit No. 853 (Light Blue/Black wire) and circuit No. 1659 (Light Blue wire). DTC 73 will also set if an open exists in circuit No. 1050 (Black or Black/White wire).

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Pressure switch monitors primary brake system pressure. Normally closed brake switch opens when brakes are applied (pressure exceeds 101 psi). If brakes are manually applied during traction control mode (if equipped), Pressure Modulator Valve (PMV) pressure switch input and brake switch input signal EBCM/EBTCM to disable traction control and allow manual braking. Pressure switch is part of PMV assembly and is not serviceable.

DTC 74 will set if EBCM/EBTCM detects open or short to ground in PMV pressure switch circuit.

Check for open in circuit No. 853 (Light Blue/Black wire) and circuit No. 1659 (Light Blue wire). Check for short to ground in circuit No. 1659 (Light Blue wire) with brakes applied. Check for PMV pressure switch failure.

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When excessive wheel spin is detected by EBTCM, EBTCM will request PCM to reduce engine torque via high speed pulse width modulated signal on circuit No. 463.

DTC 75 will set when EBTCM receives serial data message from PCM to disable Traction Control System (TCS). DTC 75 sets when EBTCM to PCM communications circuit No. 463 (Orange/Black wire) or circuit No. 800 (Tan wire) are open or shorted. PCM driveability conditions include PCM DTCs P0101, P0341, P0342, P1350, P1361, P1623, P1630, P0131, P0132, P0171 and P0172.

Note. If PCM DTC 1571 is not present, no fault exists with ABS/TCS system.

1. If DTC 75 is present, DTC 1571 should also be present. If DTC 75 is present and DTC 1571 is not present, a problem exists in PCM-to-EBTCM communications. Perform PCM DTC P1571 DIAGNOSTIC CODE CHART.

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Traction Control System (TCS) system used ABS system in conjunction with PCM fuel and ignition controls to limit drive wheel slippage during acceleration. PCM controlled portion of TCS system reduces engine torque by retarding spark advance, altering air/fuel ratio, altering boost duty cycle and/or shutting off up to 3 injectors.

To determine amount of torque reduction required, PCM monitors desired torque Pulse Width Modulated (PWM) signal (circuit No. 463) from EBTCM. PCM also provides delivered torque PWM signal via circuit No. 464, informing EBTCM how much torque is being produced by engine.

PCM DTC 1571 will set If desired torque signal PWM duty cycle is below 5 percent or above 95 percent. PCM DTC P1571 will set indicating a problem with circuit No. 463. With a current PCM DTC P1571 set, PCM will command EBTCM via circuit No. 800 to set ABS/TCS DTC 75, turn traction control off and illuminate TRACTION OFF indicator. PCM DTC P1571 does not illuminate CHECK ENGINE light.

Check for open or short to ground in circuit No. 463 (Orange/Black wire). Ensure EBTCM is providing proper PWM signal to PCM on circuit No. 463 (Orange/Black wire).

Scheme 58

Scheme 59

EBTCM shares specific serial data information supplied data line. Data line allows use of bidirectional scan tool.

A current DTC 76 cannot be read with Tech 1 due to loss of serial data communications. After data line communications are restored, DTC 76 will be stored in memory.

Check for open or short to ground in circuit No. 800 (Tan wire). Check all data line component connectors for proper terminal contact, beginning with suspect component. Check all data line components ground wiring for high resistance caused by poor terminal contact, frayed wires, etc.

Scheme 60

PCM provides EBTCM with information on engine torque output via high speed Pulse Width Modulation (PWM) signal on circuit No. 464 (Tan/Black wire). EBTCM uses this information to determine if engine management is required during wheel slip condition.

DTC 77 will set and TRACTION OFF indicator will illuminate if EBTCM determines there is a signal and/or circuit malfunction in circuit No. 464 (Tan/Black wire).

Scheme 61

Scheme 62

ANTI-LOCK WARNING LIGHT

ANTI-LOCK and TRACTION OFF (if equipped) warning lights illuminate when vehicle is first started and when a malfunction in Anti-Lock Brake System (ABS) or Traction Control System (TCS) is detected. If either light remains on longer than approximately 5 seconds after vehicle is started, or if they illuminate while driving, system will be disabled, but normal braking will continue. See DIAGNOSIS & TESTING . If BRAKE warning light comes on, check parking brake and brake fluid level. Brake failure is indicated. See BRAKE SYSTEM article in BRAKES.

REMOVAL & INSTALLATION

Note. On vehicles equipped with air bag, disable air bag system before removing EBCM/EBTCM. See SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM.

EBCM/EBTCM is located on left front strut tower. Turn ignition switch to OFF position. Rotate locking clip forward and disconnect EBCM/EBTCM harness connector. Remove 2 EBCM/EBTCM-to-strut tower nuts. To remove, slide EBCM/EBTCM up and away from strut tower. To install, reverse removal procedure. Tighten EBCM/EBTCM mounting nuts to specification. See TORQUE SPECIFICATIONS .

PRESSURE MODULATOR VALVE (PMV) ASSEMBLY

Note. Pump motor is an integral part of PMV assembly and is not serviceable separately.

Removal

1. PMV is located at lower left corner of engine compartment, behind headlight. Disconnect negative battery cable. Remove air cleaner assembly. Disconnect electrical connectors from fluid level switch, pump motor and valve block.
2. Clamp off reservoir to PMV hose. Remove hose, and install a 5/8" (15.9 mm) plug to prevent brake fluid from leaking out of reservoir. Mark all hoses and brakelines for installation reference. Disconnect primary, secondary and 4 wheel brakelines at PMV assembly. (Scheme 63)
3. Raise and support vehicle. Remove lower PMV assembly mount bolt. Lower vehicle. Remove 2 upper PMV assembly bracket bolts. Remove PMV and bracket assembly. If replacing PMV assembly, transfer necessary parts to new unit.

Installation

To install, reverse removal procedure. Tighten bolts to specification. See TORQUE SPECIFICATIONS . Fill reservoir with fluid, and bleed system. See BLEEDING BRAKE SYSTEM .

Scheme 63

WHEEL (SPEED/PULSE) SENSORS

Note. Front wheel speed sensors are not interchangeable, but rear wheel speed sensors are interchangeable.

Removal (Front)

Raise and support vehicle. Disconnect wheel speed sensor electrical connector. Remove hub/bearing assembly. Using a screwdriver, gently pry wheel speed sensor slinger from hub/bearing assembly. Gently pry wheel speed sensor from bearing, and check for contaminants or damage. Replace sensor if necessary.

Coat sensor body with Anti-Corrosion Compound (GM 1052856). Apply Loctite (620) to groove of outer diameter of bearing hub. Using Front Wheel Sensor Installer (J-38764) and a press, install sensor into hub/bearing assembly. Reconnect wheel speed sensor electrical connector.

Removal (Rear)

1. Raise and support vehicle. Remove tire and wheel assembly. Remove brake drum. Remove sensor connector from sensor. Remove bolts from hub and bearing assembly. Use wire to support brake assembly.
2. Remove hub, bearing and sensor assembly. Clean area around sensor housing mount area. DO NOT allow dirt or contaminants to fall into sensor housing. Remove sensor from hub and bearing assembly, and check for contaminants or damage. Replace if necessary.

Note. DO NOT remove grease from around toothed sensor ring, as this does not affect sensor operation. DO NOT lubricate bearing.

To install, reverse removal procedure. Tighten bolts to specification. See TORQUE SPECIFICATIONS .

ABS anti-lock diode is taped to wiring harness, near Electronic Brake Control Module (EBCM) or Electronic Brake and Traction Control Module (EBTCM). Remove tape as necessary. To install, reverse removal procedure.

Left and right proportioning valves are located at rear of vehicle. Raise and support vehicle. Disconnect brakelines from proportioning valve. Remove valve from vehicle. To install, reverse removal procedure.

Disabling System

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control) . Ensure front wheels are in straight-ahead position. Turn ignition switch to LOCK position.
2. Remove AIR BAG/SIR fuse No. 1C at instrument panel fuse block. Wait 2 MINUTES. Disconnect Yellow 2-pin SIR connector located at base of steering column. Disconnect Yellow 2-pin SIR connector located near glove box.

Activating System

Connect Yellow SIR connector located at base of steering column. Connect Yellow SIR connector located near glove box. Install AIR BAG/SIR fuse No. 1C. From passenger side of vehicle, turn ignition switch to RUN position. INFLATABLE RESTRAINT or AIR BAG warning light should flash 7-9 times, indicating system is functioning properly.

POWER BRAKE BOOSTER PISTON ROD

Note. Use the following procedure to measure how far booster piston rod protrudes from booster when vacuum is applied to booster. Piston rod is not adjustable. If piston rod protrusion is out of limits, replace power brake booster.

1. Booster does not have to be installed to perform procedure. Apply 25 in. Hg vacuum or the MAXIMUM available engine vacuum to booster. Position Piston Rod Gauge (J-37839) over piston rod.
2. One side of gauge measures minimum rod length. Other side measures maximum rod length. If piston rod length does not fall between maximum and minimum dimensions, replace brake power booster.

BRAKE PEDAL TRAVEL

Note. Brake pedal travel is not adjustable. Use the following procedure to determine if brake pedal travel is as specified.

1. Most low brake pedal problems are caused by air in hydraulic system. Bleed hydraulic system before continuing procedure. See «BLEEDING BRAKE SYSTEM»(/buick/lesabre/vii-1992-1999/remont/anti-locktraction-control/#anti-lock-brake-system-traction-control) . Other possible causes of excessive pedal travel are incorrect power booster push rod length, parking brake adjustment, frozen rear brake shoe adjustors, worn linings, or a leak in hydraulic system.
2. With engine off, pump brake pedal until all vacuum reserve is exhausted from power brake booster. A definite change in pedal feel will occur. Install Brake Pedal Effort Gauge (J-28662) onto brake pedal. Hook end of tape measure over top of brake pedal. Measure and record distance to rim of steering wheel.
3. Apply 100 lbs. (45 kg) of force to brake pedal. Measure and record distance to rim of steering wheel again. Difference between measured values is brake pedal travel. If brake pedal travel is more than 2.24" (57 mm), check rear brake adjuster mechanism for proper operation and adjustment.
4. If pedal is low, soft or spongy, bleed brake system. Also check for hydraulic leak, parking brake adjustment, master cylinder push rod length and rear brake shoe wear.

STOPLIGHT SWITCH

1. Install electrical connectors and cruise vacuum line on stoplight switch. (Scheme 64) Fully depress brake pedal. Insert switch assembly into mounting bracket. Press switch assembly inward until no clicks are heard.
2. Pull brake pedal rearward until no clicks are heard. Release pedal and pull it rearward again to ensure switch assembly is fully seated.
3. When properly installed, notch in switch plunger should be visible. (Scheme 64) If assembly is not properly installed, repeat steps 1) and 2).

Scheme 64

PARKING BRAKE

Note. If brakes have been serviced, parking brake must be adjusted to prevent premature brake wear.

1. Raise and support vehicle. Adjust rear brakes. See «BRAKE SYSTEM»(/buick/lesabre/vii-1992-1999/remont/mechanical-hydraulic/#disc-brake-system-drum-brake-system) article in BRAKES. Apply parking brake to 6 clicks (ratchets) and release. Do this 5 times.
2. To ensure parking brake pedal is fully released, turn ignition on. BRAKE indicator light on instrument panel should be off. If light is off, go to next step. If light is on, verify pedal is fully released and pull front parking brake cable downward to remove slack.
3. Raise and support vehicle. At parking brake cable adjuster, rotate adjuster nut until a 1/8" (3.2 mm) drill bit can be inserted through access hole into space between shoe web and parking brake lever. Cable is adjusted properly when a 1/8" (3.2 mm) drill bit will fit into space, but a 1/4" (6.4 mm) drill bit will not fit.
4. Apply parking brake to one click. Wheels should not turn when trying to turn wheels forward by hand. Wheels should drag or not turn when trying to turn wheels in reverse direction by hand. Release parking brake. Ensure wheels rotate freely. Install access hole plugs. Lower vehicle.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

ABS/TCS Wiring Diagram (1 Of 2). Scheme 65

ABS/TCS Wiring Diagram (2 Of 2). Scheme 66

See also:
• BRAKE SYSTEM
• DIAGNOSIS & TESTING
• INTERMITTENTS & POOR CONNECTIONS
• SYMPTOM DIAGNOSIS