Saturn Coupes/Sedans/Wagons 1991-1998 Repair Guide

ABS Control Assembly

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The ABS control assembly consists of the solenoid valves, master cylinder and hydraulic modulator.

REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4, 5 and 6


CAUTION
The ABS modulator pistons are normally in the HOME or top position. In this position, the modulator drive gears are under spring tension and will turn during disassembly if not unloaded. The sudden rotation of gears and release of tension could cause injury if done without extreme care. It is recommended that the pistons be run down and the tension released prior to removing the brake control assembly, if the unit is to be disassembled.

  1. If removing the unit for disassembly, connect the Saturn Portable Diagnostic Tool (PDT), or an equivalent scan tool, and perform the RUN ABS MOTORS, PISTONS DOWN-REL test to run the modulator pistons down and release spring tension.
  2.  
  3. Remove the air cleaner/induction assembly.
  4.  
  5. Disconnect the negative battery cable, then remove the battery box and battery from the vehicle.
  6.  
  7. Tag and unplug the 2 electrical connectors from the solenoids and the connector from the brake fluid level sensor on the lower side of the fluid reservoir.
  8.  
  9. Remove the CPA device from the motor pack 6-way connector and disengage the connector from the bottom of the motor pack.
  10.  
  11. Position a cloth to catch any escaping fluid, then tag and disconnect the brake lines from the control assembly. Plug the openings to prevent excessive fluid contamination or loss.
  12.  


WARNING
Once the brake lines are disconnected, do not excessively pull or bend the lines away from the module, or the lines may be damaged.

  1. Remove the 2 brake control assembly-to-brake booster retaining nuts and remove the assembly.
  2.  
  3. If necessary, disassemble the unit as follows:
    1. Remove the 6 gear cover Torx® screws from the bottom of the assembly and remove the cover. If the entire motor pack assembly is being replaced, skip to Step C, and then to the assembly procedure.
    2.  
    3. Mark the location of the modulator drive gears for reassembly. Insert a small suitable prybar between the holes in the gears to keep them from moving and remove the 3 gear-to-driveshaft retaining nuts. Remove the gears from the modulator.
    4.  

  4.  


WARNING
Do not allow the gears to turn while removing the driveshaft nuts, or the piston may hit the top of the modulator bore and damage the pistons.

  1. Remove the motor pack-to-modulator Torx® screws and separate the motor pack from the modulator.
  2.  
  3. Remove the 2 modulator-to-master cylinder through-bolts and separate the master cylinder from the assembly.
  4.  
  5. Remove the 2 transfer tubes and O-rings from the master cylinder and modulator.
  6.  
  7. Remove the through-bolt O-rings from the master cylinder and modulator.
  8.  

To install:
  1. If necessary, assemble the ABS control unit as follows:
    1. Lubricate the new transfer tube O-rings with clean brake fluid. Press the NEW tubes and O-rings into the modulator by hand until fully bottomed.
    2.  
    3. Lubricate the new through-bolt O-rings with clean fluid and install the rings into the master cylinder and modulator.
    4.  
    5. Install the master cylinder onto the modulator, and press the transfer tubes into position on the master cylinder.
    6.  
    7. Install the through-bolts and tighten to 146 inch lbs. (16.5 Nm).
    8.  
    9. Position the drive gears onto the driveshafts as noted earlier. Hold the gears from turning and tighten the retaining nuts to 75 inch lbs. (8.5 Nm).
    10.  
    11. Hold the modulator upside down with the gears facing you and carefully rotate each gear counterclockwise until movement stops. This will position the pistons close to the top or HOME position and simplify the bleeding procedure.
    12.  
    13. Position the motor pack to the modulator, aligning the gears, and install the 4 motor pack retaining screws. Tighten the screws to 40 inch lbs. (4.5 Nm).
    14.  
    15. Install the gear cover onto the modulator assembly with the 6 retaining screws, then tighten the screws to 20 inch lbs. (2.25 Nm).
    16.  

  2.  
  3. Position the control assembly onto the brake booster studs, then install the retaining nuts and tighten to 20 ft. lbs. (27 Nm).
  4.  
  5. Position the brake lines into the control assembly as originally noted and tighten the fittings to 24 ft. lbs. (32 Nm).
  6.  

From the front of the master cylinder moving rearward, the lines are: LF, RR, LR and RF.

  1. Install the 6-way wiring harness connector and insert the CPA device. Install the wiring harness connectors to the brake fluid level and 2 solenoid valve electrical connectors.
  2.  
  3. Install the battery and hold-down device. Connect the positive battery cable first, then the negative battery cable.
  4.  
  5. Install the air cleaner/induction assembly.
  6.  



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Fig. Fig. 1: Label and disconnect the wiring harnesses and brake lines from the control assembly



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Fig. Fig. 2: Remove the control assembly from the brake booster



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Fig. Fig. 3: View of the control assembly from the driver' side of the vehicle



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Fig. Fig. 4: Exploded view of the control assembly

  1. If the ABS pistons were run down for unit disassembly, connect the scan tool and perform the RUN ABS MOTORS, PISTONS UP-HOME test to restore tension to the modulator gears before moving the vehicle.
  2.  


CAUTION
Never attempt to move the vehicle with the modulator pistons in the DOWN position! With the tension released and the piston free to travel, the master cylinder must first fill the piston bores (force the pistons downward with brake fluid) before effective braking can occur. This will cause excessive brake pedal travel and reduced braking until the system is initialized (at a speed greater than 3 MPH) and the pistons are run back to the HOME position.

  1. Fill the reservoir with clean brake fluid and properly bleed the ABS system.
  2.  



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Fig. Fig. 5: Use a small prybar in the holes to secure the modulator gears and loosen the driveshaft nuts



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Fig. Fig. 6: Gently turn the gears by hand to position the pistons towards the top of the modulator bores

TESTING



See Figure 7

  1. Disengage the ABS motor pack connector.
  2.  
  3. Using a Digital Volt/Ohmmeter (DVOM), measure the voltage at circuit E, A or C of the motor pack connector with the key ON . Which circuit is being checked depends on which trouble code is set.
  4.  
  5. If battery voltage is present, the circuit is shorted to voltage. If battery voltage is not present, measure the voltage at circuit(s) F, B and/or D.
  6.  
  7. If battery voltage is not present, the ABS motor pack is at fault.
  8.  
  9. Turn the key OFF and disconnect the negative battery cable.
  10.  
  11. With the DVOM at the ohmmeter setting, measure the resistance to ground of the motor circuit to be tested.
  12.  
  13. If the resistance measures above 200 ohms, the ABS motor pack is at fault.
  14.  



Click image to see an enlarged view

Fig. Fig. 7: ABS motor pack circuit schematic

 
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