Reduction Gear Service

Complete service of the electric drive unit reduction gear, including removal, inspection, fluid replacement, and reinstallation of the single-speed transmission assembly.

Warnings

Tools required

Parts

• Reduction gear cover gasket × 1 — Use OEM specification
• Drain plug washer × 1 — Use OEM specification
• Fill plug O-ring × 1 — Use OEM specification
• Drive unit filter (if equipped) × 1 — Use OEM specification
• Output shaft seal × 2 — Use OEM specification

Fluids

• ACDelco Dexron VI ATF — 13.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Place wheel chocks behind rear wheels
3. Disconnect 12V auxiliary battery negative terminal and wait 2 minutes
4. Remove high-voltage service disconnect located under rear seat (requires removing seat cushion)
5. Verify high-voltage system is de-energized using insulated multimeter on HV battery terminals
6. Install high-voltage lockout tag and retain service plug in secure location
7. Wait minimum 15 minutes for capacitor discharge
8. Raise vehicle on lift to working height
9. Remove front wheels
10. Remove engine undershield and splash shields
11. Place transmission jack or support fixture under drive unit

Procedure

1. 1

   Disconnect high-voltage cables from drive unit
   Wearing high-voltage insulated gloves, remove the high-voltage connector bolts securing the orange HV cables to the motor assembly. Carefully support the cable connectors and move them away from the work area. Cover exposed terminals with insulating caps.
   ⚠️Verify system de-energization with multimeter before touching any HV connectors. Even with service plug removed, residual voltage may be present.
   Torque spec

   Connector Bolts7 Nm (5 lb-ft)
2. 2

   Disconnect low-voltage connections and sensors
   Disconnect the resolver/encoder connector, temperature sensor connector, and any other low-voltage connections from the drive unit. Remove sensor bolts securing position sensors to the housing. Label all connections for proper reassembly.
   Torque spec

   Sensor Bolts11 Nm (8 lb-ft)

   Connector Bolts7 Nm (5 lb-ft)
3. 3

   Remove motor mounting brackets
   Support the drive unit weight with transmission jack. Remove the upper and lower motor mount bolts connecting the drive unit to the subframe and body. Remove any bracket bolts securing supporting brackets to the drive unit housing.
   ⚠Drive unit weighs approximately 170 lbs. Ensure adequate support before removing final mounting bolts.
   Torque spec

   Motor Mount Bolts75 Nm (55 lb-ft)

   Bracket Bolts20 Nm (15 lb-ft)
4. 4

   Disconnect axle shafts
   Remove the axle shaft mounting bolts from both driver and passenger side CV joints at the drive unit output flanges. Use a pry bar to carefully separate the shafts from the output flanges. Support axle shafts with wire to prevent damage to CV boots.
   Torque spec

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

   Lower and remove drive unit assembly
   Verify all connections, mounts, and fasteners have been removed. Carefully lower the drive unit assembly using the transmission jack. Navigate the unit away from the subframe and remove from under the vehicle. Place on clean workbench for service.
   ⚠Guide HV cable connectors carefully during removal to avoid damage. Do not allow drive unit to hang by cables or hoses.
6. 6

   Drain reduction gear fluid
   Position drain pan under drive unit. Remove the drain plug from the bottom of the reduction gear housing. Allow fluid to drain completely (approximately 10-15 minutes). Inspect drained fluid for metal particles or debris indicating internal wear. Remove and discard drain plug washer.
   ⚠Fluid may still be warm. Wear appropriate gloves and eye protection.
7. 7

   Remove reduction gear cover
   Remove all cover screws securing the reduction gear cover to the main housing. Carefully separate the cover using plastic pry tools if necessary. Remove and discard the cover gasket. Inspect the cover for cracks or damage.
   Torque spec

   Cover Screws11 Nm (8 lb-ft)
8. 8

   Inspect reduction gear components
   Visually inspect the reduction gear set, bearings, and shafts for wear, scoring, or damage. Check gear teeth for pitting, excessive wear, or chipping. Inspect the differential assembly for proper operation. Remove and replace the internal filter if equipped. Document any abnormal wear patterns.
   ℹ️If significant gear wear or damage is observed, consult GM service bulletin for complete drive unit replacement criteria.
9. 9

   Replace output shaft seals
   Remove both output shaft seals using seal puller or appropriate tool. Clean seal bores thoroughly. Install new output shaft seals using seal driver, ensuring proper depth and alignment. Lubricate seal lips with fresh Dexron VI before installation.
   ⚠Do not damage seal bores during removal. Nicked or damaged bores will cause leaks.
10. 10

    Clean and prepare for reassembly
    Thoroughly clean all mating surfaces on the housing and cover using plastic scraper and brake cleaner. Remove all old gasket material. Inspect mating surfaces for warping or damage. Clean the fill plug opening and threads.
    ℹ️Ensure no cleaning residue or debris remains inside the housing before reassembly.
11. 11

    Reinstall reduction gear cover
    Install new cover gasket on housing mating surface. Position cover carefully onto housing, ensuring proper alignment of dowel pins. Install all cover screws and tighten in a cross-pattern to specified torque. Verify gasket is properly seated all around.
    Torque spec

    Cover Screws11 Nm (8 lb-ft)
12. 12

    Refill reduction gear with fluid
    Install new drain plug washer and reinstall drain plug to specified torque. Using fluid pump, fill the reduction gear through the fill port with 13.5 quarts of ACDelco Dexron VI ATF. Fill until fluid begins to escape from fill port. Install new fill plug O-ring and reinstall fill plug. Verify no leaks from drain or fill plugs.
    ℹ️Use only Dexron VI ATF. Other transmission fluids are not compatible and will cause damage.
13. 13

    Reinstall drive unit to vehicle
    Using transmission jack, carefully raise drive unit assembly into position. Align motor mounts with mounting points on subframe and body. Install motor mount bolts and tighten to specified torque. Ensure drive unit is properly seated in all mounting locations.
    ⚠Guide HV cables carefully during installation to prevent pinching or damage.
    Torque spec

    Motor Mount Bolts75 Nm (55 lb-ft)

    Bracket Bolts20 Nm (15 lb-ft)
14. 14

    Reconnect axle shafts and sensors
    Reconnect both axle shafts to output flanges. Install mounting bolts and torque to specification. Reinstall all position sensors with new sensor bolts torqued to specification. Reconnect all low-voltage electrical connectors using labeled references from disassembly.
    Torque spec

    Mounting Bolts27 Nm (20 lb-ft)

    Sensor Bolts11 Nm (8 lb-ft)

    Connector Bolts7 Nm (5 lb-ft)
15. 15

    Reconnect high-voltage system
    Wearing high-voltage insulated gloves, remove insulating caps from HV terminals. Position HV cable connectors onto motor terminals. Install high-voltage connector bolts and torque to specification. Verify all HV connections are secure and properly seated. Reinstall high-voltage service disconnect plug under rear seat.
    ⚠️Ensure HV connector bolts are torqued precisely to specification. Improper torque can cause arcing, overheating, or connection failure.
    Torque spec

    Connector Bolts7 Nm (5 lb-ft)

Reassembly

1. Reinstall splash shields and engine undershield
2. Reinstall front wheels and torque lug nuts to specification
3. Lower vehicle to ground
4. Reconnect 12V auxiliary battery negative terminal
5. Verify high-voltage service disconnect is properly installed and locked
6. Clear any diagnostic trouble codes using factory scan tool

Verification

• Start vehicle and verify 'READY' indicator illuminates without error messages
• Check for fluid leaks around reduction gear cover, drain plug, and fill plug
• Check for fluid leaks at output shaft seals
• Perform test drive including forward, reverse, and regenerative braking
• Listen for abnormal noises from drive unit during operation
• Verify smooth acceleration and deceleration without vibration
• Monitor drive unit temperature during test drive for normal operating range
• Recheck fluid level after test drive and top off if necessary
• Scan for diagnostic trouble codes and verify no new codes are present

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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