ABS Pump

Remove and replace the ABS hydraulic control unit (ABS pump) on a 2023 Chevrolet Bolt EUV, including brake system bleeding and verification.

Warnings

Tools required

Parts

• ABS hydraulic control unit assembly × 1 — Use OEM specification
• Brake line sealing washers × 6 — Replace all connection washers
• Thread locker (medium strength) × 1 — Loctite 243 or equivalent

Fluids

• ACDelco DOT 4 Brake Fluid — 1.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Verify 12V battery is fully charged (critical for scan tool bleeding procedure)
3. Chock rear wheels securely
4. Raise front of vehicle and support on jack stands rated for EV weight (Bolt EUV is approximately 3650 lbs)
5. Remove both front wheels
6. Place drain pan beneath master cylinder and ABS unit location
7. Remove engine cover if equipped
8. Extract as much brake fluid as possible from master cylinder reservoir using turkey baster or extraction pump

Procedure

1. 1

   Access ABS unit
   Locate the ABS hydraulic control unit in the engine compartment on the driver's side near the strut tower. Remove any plastic covers or air intake ducting that obstructs access. The unit is mounted vertically with multiple brake lines connected.
2. 2

   Disconnect electrical connector
   Depress the locking tab on the ABS unit electrical connector and carefully disconnect it. Move the wiring harness aside and secure it so it doesn't interfere with brake line removal.
3. 3

   Mark and remove brake lines
   Photograph or mark each brake line connection for reference during installation. Using a line wrench, carefully loosen all brake line fittings at the ABS unit (typically 5-6 lines). Work slowly to avoid rounding off fittings. Allow brake fluid to drain into the pan. Cap or plug open lines immediately to prevent contamination.
   ⚠Use only a properly sized line wrench to prevent rounding off brake line fittings. Standard wrenches will likely damage the soft metal.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)
4. 4

   Remove ABS unit mounting bolts
   Locate the mounting bolts securing the ABS unit to its bracket (typically 2-3 bolts). Support the unit with one hand while removing the mounting bolts with the other. Carefully lower the ABS unit away from the vehicle, taking care not to damage any remaining brake line stubs.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
5. 5

   Prepare new ABS unit
   Remove the new ABS unit from packaging and verify all electrical connector pins are undamaged. Inspect all brake line ports and ensure they are clean and free of debris. Have new sealing washers ready for installation.
6. 6

   Install new ABS unit
   Position the new ABS unit onto the mounting bracket, aligning the mounting holes. Install mounting bolts and tighten to specification. Ensure the unit is stable and properly seated before proceeding to brake line connections.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
7. 7

   Connect brake lines
   Install new sealing washers on all brake line fittings. Thread each brake line into the correct port on the ABS unit by hand first, referring to your photos or marks from removal. Once all lines are hand-tight, use a line wrench to torque each fitting to specification in sequence. Do not cross-thread fittings.
   ⚠Cross-threading brake line fittings will ruin the ABS unit. Always thread fittings by hand first and ensure they turn smoothly before using a wrench.
   Torque spec

   Line Fittings20 Nm (15 lb-ft)
8. 8

   Reconnect electrical connector
   Clean the electrical connector with electrical contact cleaner if needed. Reconnect the ABS unit electrical connector, ensuring it clicks securely into place. Verify the locking tab is fully engaged.
9. 9

   Fill brake fluid reservoir
   Fill the master cylinder reservoir to the MAX line with fresh ACDelco DOT 4 brake fluid. Keep the reservoir topped up throughout the bleeding process to prevent air ingestion.
10. 10

    Perform manual brake bleeding
    Starting with the wheel furthest from the master cylinder (right rear), then left rear, right front, left front: attach bleeder hose to bleeder screw, have assistant pump brake pedal 3-4 times and hold, open bleeder screw to release fluid and air, close bleeder screw before pedal reaches floor, repeat until fluid flows clear without bubbles. Torque bleeder screws to specification after bleeding each corner.
    ⚠Never allow the brake pedal to reach the floor during bleeding, as this can damage the master cylinder seals.
    Torque spec

    Bleeder Screw10 Nm (7 lb-ft)
11. 11

    Perform ABS automated bleeding
    Connect scan tool and navigate to ABS bleeding function for 2023 Bolt EUV. Follow scan tool prompts to activate ABS solenoids in sequence. Monitor brake fluid reservoir level constantly and refill as needed. The scan tool will cycle each ABS valve to purge trapped air. After automated bleeding completes, repeat manual bleeding procedure at all four wheels to remove any air displaced from ABS unit.
12. 12

    Reinstall wheels and lower vehicle
    Reinstall front wheels and torque lug nuts to specification in a star pattern. Remove jack stands and carefully lower vehicle to ground. Perform final lug nut torque verification with wheels on ground.
    Torque spec

    Wheel Lug Nuts136 Nm (100 lb-ft)

Reassembly

1. Reinstall any engine covers or air intake ducting that was removed for access
2. Top off brake fluid reservoir to MAX line with fresh DOT 4 fluid
3. Clear any ABS fault codes using scan tool if present
4. Verify ABS warning light extinguishes after starting vehicle

Verification

• Start engine and verify ABS warning light illuminates briefly then turns off (normal system check)
• With engine running, firmly depress brake pedal and hold for 30 seconds - pedal should remain firm with no sinking
• Check all brake line connections at ABS unit for leaks while assistant holds brake pedal
• Perform test drive in safe area at low speed (under 15 mph) to verify normal brake operation and pedal feel
• Perform ABS activation test in safe area on dry pavement by firmly braking from 25 mph - ABS should activate normally with pulsing pedal feedback
• Re-check brake fluid level after test drive and top off if needed
• Use scan tool to verify no ABS fault codes are present after test drive
• Inspect all brake line connections one final time for any signs of seepage or leaks

More procedures for this vehicle