Maytag MDB8959SKZ – Drain pump failure Repair Guide

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Model: Maytag MDB8959SKZ
Brand: Maytag
Model Number: MDB8959SKZ

🔍 Problem Description

Test pump motor; check impeller for damage; replace pump

📋 What You’ll Need

  • Drain pump
  • Multimeter

    • 🔧 Step-by-Step Repair Instructions

      🔧 Step 1: Test drain pump motor with multimeter

      1. Set your digital multimeter to the ohms (Ω) setting at 200 ohms or the lowest resistance setting available.
      2. Open the dishwasher door and remove the bottom dish rack by lifting it straight up and out.
      3. Unscrew the 6 Torx T20 screws securing the lower spray arm assembly and lift it out to expose the sump cover.
      4. Remove the 4 Phillips-head #2 screws around the perimeter of the circular gray sump cover, located in the center of the dishwasher floor.
      5. Lift the sump cover straight up and set it aside to reveal the drain pump assembly directly below.
      6. Locate the drain pump motor on the left side of the sump housing—it’s a black cylindrical component approximately 3 inches in diameter with two wire terminals on top.
      7. Press the plastic tab on the wire connector attached to the pump motor terminals and pull the connector straight off, exposing two metal blade terminals.
      8. Touch one multimeter probe to each of the two exposed terminals on the pump motor (polarity doesn’t matter for resistance testing).
      9. Read the resistance value on your multimeter display—a functional drain pump motor will show between 15 and 40 ohms of resistance.
      10. If the multimeter displays “OL” (overload) or a number above 100 ohms, the motor winding is open and the pump has failed.
      11. If the multimeter displays 0 ohms or near-zero, the motor winding is shorted and the pump has failed.
      12. Test for a ground fault by touching one probe to either terminal and the other probe to the metal pump housing—the reading should be “OL” (infinite resistance); any continuity reading indicates a failed pump that is grounding out.

      🛠️ Step 2: Check pump impeller for damage

      1. Locate the pump assembly cover at the bottom center of the dishwasher tub, directly beneath where the lower spray arm sits.
      2. Grasp the lower spray arm and pull straight up to remove it from the spray arm mount—it requires no tools and lifts off with 3-5 pounds of upward force.
      3. Remove the spray arm support by turning it counterclockwise one-quarter turn (90 degrees) until it releases, then lift it straight up and set aside.
      4. Identify the circular pump cover (approximately 5 inches in diameter) with a center cap visible in the sump area.
      5. Turn the pump cover counterclockwise one-quarter turn and lift it straight up to remove it—this exposes the pump housing.
      6. Look down into the pump housing and locate the white or gray plastic impeller with multiple curved blades radiating from a center hub.
      7. Insert your index finger into the pump housing and attempt to rotate the impeller clockwise and counterclockwise—it should spin freely with minimal resistance.
      8. Inspect each impeller blade for these specific damage indicators:
      9. Check the center hub where the impeller mounts to the motor shaft for cracks radiating outward toward the blades.
      10. Feel along the outer edges of the impeller for any rough or sharp areas indicating wear or damage.
      11. If the impeller shows any cracks, missing pieces, excessive wear, or does not spin freely, note that it requires replacement with part number W11032770.
      12. If the impeller appears intact with no visible damage and spins freely without grinding sounds, it passes inspection and requires no replacement.

      ⚙️ Step 3: Inspect pump housing for obstructions

      1. Locate the pump housing assembly, which is the gray or black cylindrical component positioned directly beneath the filter screen you removed in Step 2, centered at the bottom of the dishwasher tub.
      2. Grasp the pump cover (circular piece approximately 4 inches in diameter) and rotate it counterclockwise one-quarter turn until it releases from the bayonet-style lock tabs.
      3. Lift the pump cover straight up and set it aside on your work surface.
      4. Look inside the now-exposed pump chamber – you’ll see the white or cream-colored impeller with 6 fins at the bottom of the cylindrical opening, approximately 3 inches deep.
      5. Insert your index finger into the chamber and manually rotate the impeller clockwise through several complete rotations to check for resistance or grinding sensations that indicate debris.
      6. Remove any visible obstructions using needle-nose pliers: common items include small bone fragments, toothpicks, fruit pits, pieces of broken glass, or twist ties lodged between the impeller fins or chamber walls.
      7. Shine a flashlight into the pump chamber at different angles to identify any debris stuck to the sides or trapped beneath the impeller edges.
      8. Use a damp cloth to wipe the interior walls of the pump chamber, removing any food residue, grease buildup, or mineral deposits.
      9. Check the pump inlet port (the opening at the 6 o’clock position when facing the chamber) for blockages by inserting a straightened wire coat hanger or pipe cleaner 2-3 inches into the opening.
      10. Verify the impeller now spins freely by rotating it again with your finger – it should complete multiple rotations with light resistance and no grinding sounds.
      11. Examine the rubber seal on the underside of the pump cover for cracks, tears, or deformation – the seal should be uniform, pliable, and approximately 3mm thick around its entire circumference.

      🔩 Step 4: Test pump operation

      1. Locate the service panel at the bottom front of the dishwasher, directly beneath the door, and remove it by pulling the bottom edge toward you until the clips release.
      2. Identify the drain pump assembly on the right side of the tub base, approximately 8 inches from the right wall – it’s a cylindrical black unit about 4 inches in diameter with two wire connectors attached.
      3. Trace the wire harness from the drain pump to find the circulation pump motor on the left side, positioned 6 inches from the left wall – this is a larger silver cylindrical motor with a white wire connector.
      4. Press the power button on the control panel to turn the dishwasher on without closing the door.
      5. Press and hold the “Heavy Duty” and “Normal” buttons simultaneously for 3 seconds until you hear a beep – this activates diagnostic mode.
      6. Press the “Start/Resume” button once to advance to the drain pump test cycle (the display will show “01” or the drain light will illuminate).
      7. Listen for the drain pump motor to activate – you’ll hear a distinct humming sound increasing in pitch over 2-3 seconds, reaching approximately 60 decibels.
      8. Watch the drain pump impeller housing while the pump runs – place your hand 2 inches away to feel for vibration, which indicates the motor is engaging properly.
      9. Press “Start/Resume” again to advance to circulation pump test (display shows “02” or wash light illuminates).
      10. Listen for the circulation pump to start – this produces a louder, deeper hum than the drain pump, approximately 65-70 decibels.
      11. Feel the circulation pump motor housing for steady vibration without any grinding, clicking, or rattling sounds.
      12. Press “Cancel” twice to exit diagnostic mode once both pumps have run for 30 seconds each without abnormal sounds or failure to start.

      đź“‹ Step 5: Replace drain pump if motor fails or impeller is damaged

      1. Locate the drain pump assembly at the bottom center of the dishwasher tub, directly beneath where the spray arm rotates.
      2. Disconnect the electrical connector from the pump motor by pressing the locking tab on the top of the white rectangular connector and pulling straight away from the pump body.
      3. Use slip-joint pliers to compress the clamp on the ribbed drain hose (black corrugated hose approximately 1.5 inches in diameter) and slide the clamp 2-3 inches back along the hose.
      4. Pull the drain hose straight off the pump outlet port with a twisting motion—expect residual water to drain out (approximately 1/4 cup).
      5. Locate three T20 Torx screws securing the pump assembly to the sump housing, positioned in a triangular pattern approximately 2 inches apart.
      6. Remove all three T20 Torx screws and set aside.
      7. Rotate the entire pump assembly counterclockwise 1/4 turn (90 degrees) to disengage it from the bayonet-style mounting tabs.
      8. Lift the pump assembly straight up and out of the sump housing—you’ll feel it release after lifting approximately 1 inch.
      9. Position the new drain pump (part number W11032770) with the outlet port facing toward the right side of the dishwasher.
      10. Lower the pump into the sump housing opening until the mounting tabs align with the slots in the housing.
      11. Rotate the pump clockwise 1/4 turn until it stops—the pump will seat firmly and you’ll feel it lock into position.
      12. Insert and tighten the three T20 Torx screws until snug (approximately 18-20 inch-pounds—firm hand pressure on a 6-inch screwdriver).
      13. Push the drain hose onto the pump outlet port until it bottoms out (approximately 1.5 inches of insertion depth).
      14. Slide the hose clamp back to within 1/4 inch of the pump connection point.
      15. Reconnect the white electrical connector to the pump motor terminals—the connector will click audibly when fully seated.

      đź›’ Recommended Products

      Here are the recommended products for this repair: