Transmission Flush

Complete transmission fluid flush and filter replacement for the Mercedes-Benz 722.9 NAG2 7-speed automatic transmission, including pan removal, filter replacement, and fluid refill.

Warnings

Tools required

Parts

• Mercedes-Benz 722.9 transmission filter kit with gasket × 1 — A1402770095 or equivalent OEM
• Transmission oil pan gasket × 1 — A1402710080 or included in filter kit
• Transmission drain plug seal/crush washer × 1 — Use OEM specification
• Transmission conductor plate gasket set (if replacing) × 1 — A1402770395 - recommended if over 60k miles

Fluids

• Mercedes-Benz ATF 134 — 10 qt

Preparation

1. Ensure transmission is cold (below 100°F). Vehicle must have been off for at least 2 hours.
2. Park vehicle on level surface and engage parking brake.
3. Raise vehicle on lift or support securely on jack stands at all four corners. Verify vehicle is completely level for accurate fluid fill.
4. Remove engine undercover panels and transmission protective covers to access transmission pan.
5. Connect diagnostic scan tool and verify communication with transmission control module (TCU).
6. Have all replacement parts, fluids, and tools readily accessible before beginning drain procedure.
7. Position large drain pan under transmission - initial drain will release 6-8 quarts rapidly.

Procedure

1. 1

   Drain transmission fluid via drain plug
   Locate the transmission drain plug on the bottom of the transmission pan. Using appropriate socket, carefully loosen the drain plug. Allow fluid to drain completely into drain pan - this will take 5-10 minutes. Once drained, remove and inspect drain plug and sealing washer. Discard old crush washer and install new washer on drain plug. Reinstall drain plug hand-tight, then torque to specification.
   Torque spec

   Transmission Drain Plug30 Nm (22 lb-ft)
2. 2

   Remove transmission pan bolts
   Using T25 Torx bit, loosen all transmission pan bolts in a criss-cross pattern, working from outside edges toward center. Do not fully remove bolts initially - loosen each 3-4 turns to allow remaining fluid to seep out gradually. Once fluid stops dripping, remove all pan bolts completely and set aside. Note: Approximately 2-3 additional quarts will drain when pan is removed.
   Torque spec

   Pan Bolts22 Nm (16 lb-ft)
3. 3

   Remove transmission oil pan
   Gently tap pan with rubber mallet to break gasket seal. Carefully lower pan while keeping level to avoid spilling residual fluid. Inspect interior of pan for metal debris, clutch material, or excessive sludge - any significant debris indicates internal transmission wear requiring further diagnosis. Clean pan thoroughly with solvent and shop towels, removing all old gasket material from sealing surface. Inspect pan for cracks or damage.
4. 4

   Remove old transmission filter
   Locate the transmission filter assembly mounted to valve body. The filter has multiple bolts/screws securing it. Carefully remove mounting fasteners and pull filter straight down to disengage from valve body. Some additional fluid will drain from filter cavity. Inspect filter housing and O-rings for damage. Clean filter mounting surface on valve body with lint-free cloth, ensuring no debris falls into valve body passages.
5. 5

   Install new transmission filter
   Remove new filter from packaging and verify all O-rings and seals are properly seated. Lightly lubricate O-rings with clean ATF. Align filter carefully with valve body mounting points and press firmly upward until fully seated. Install all filter mounting fasteners and torque to specification in criss-cross pattern. Verify filter is securely mounted with no gaps.
   Torque spec

   Cover Screws15 Nm (11 lb-ft)
6. 6

   Install new pan gasket and reinstall pan
   Place new transmission pan gasket on clean pan, ensuring all bolt holes align correctly. Some gaskets are adhesive-backed; others require careful alignment during installation. Lift pan into position, aligning gasket with transmission case. Start all pan bolts by hand, threading each 2-3 turns before tightening any. Once all bolts are started, torque in criss-cross pattern from center outward to specification. Perform final torque check on all bolts.
   Torque spec

   Pan Bolts22 Nm (16 lb-ft)
7. 7

   Initial fluid fill via dipstick tube
   Locate transmission dipstick tube (if equipped) or fill plug on side of transmission. Using fluid pump or funnel with long flexible hose, add approximately 5 quarts of Mercedes-Benz ATF 134 through fill port. Pour slowly to prevent overflow and air pocket formation. This initial fill gets fluid to valve body and pump for startup. Do not overfill at this stage.
8. 8

   Start engine and circulate fluid
   With scan tool connected and monitoring transmission temperature, start engine and allow to idle. Transmission temperature must be between 30-50°C (86-122°F) for initial circulation. With foot on brake, slowly shift through all gear positions (P-R-N-D and manual modes), pausing 3-5 seconds in each position. Return to Park. This circulates fluid through all clutch packs and passages. Monitor for any leaks around pan gasket and drain plug.
9. 9

   Check fluid level and add to specification
   With engine running at idle and transmission in Park, monitor transmission temperature using scan tool. Temperature must reach exactly 30-40°C (86-104°F) for accurate level check. Access fluid level check procedure in scan tool (actual procedures vary by tool). Add fluid in small increments (0.5 quart) until scan tool indicates proper level OR fluid appears at check plug opening if using plug method. Mercedes 722.9 specification requires approximately 9.5-10 quarts total.
10. 10

    Perform final fluid level calibration
    Using scan tool, perform transmission fluid temperature adaptation/learning procedure per manufacturer instructions. Bring transmission fluid to operating temperature of 80-100°C (176-212°F) by driving vehicle or using scan tool active test functions. Once at temperature, verify fluid level again - add or drain small amounts as necessary. Final level must be checked at specified temperature with engine running, transmission in Park, on level surface. Record final fluid quantity added.

Reassembly

1. Reinstall all transmission protective covers and engine undercovers removed during preparation.
2. Clear any diagnostic trouble codes from transmission control module using scan tool.
3. Reset transmission adaptation values if recommended by scan tool software for fluid change procedure.
4. Lower vehicle from lift or jack stands and perform final ground-level inspection for leaks.

Verification

• Test drive vehicle through all gears, verifying smooth shifts with no slipping, flaring, or harshness. Allow transmission to reach full operating temperature during test drive.
• After test drive, recheck fluid level at proper temperature (80-100°C) with engine running and transmission in Park on level surface. Adjust if necessary.
• Inspect transmission pan, drain plug, and filter area for any signs of fluid leakage. Address any leaks immediately.
• Using scan tool, verify no new transmission fault codes are present and all system parameters read normal.
• Document service date, mileage, and total fluid quantity used for maintenance records. Reset service interval in vehicle if applicable.

Related trouble codes on this vehicle

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

Chasing one of these codes and not sure which part is guilty? Ask a master mechanic about YOUR car →

More procedures for this vehicle