Transmission Oil Cooler

Remove and replace the transmission oil cooler, including draining transmission fluid, disconnecting cooler lines, removing the cooler assembly from its mounting location, and refilling the transmission system.

Warnings

Tools required

Parts

• Transmission oil cooler assembly × 1 — Use OEM specification
• Transmission cooler line O-rings × 4 — Use OEM specification
• Transmission cooler mounting hardware kit × 1 — Use OEM specification if reusing is not possible

Fluids

• Touchtronic 6-speed ZF ATF — 9.5 qt

Preparation

1. Park vehicle on level surface and apply parking brake. Place wheel chocks behind rear wheels.
2. Allow engine and transmission to cool for minimum 2 hours if vehicle was recently operated.
3. Raise vehicle on lift or jack stands to provide adequate working clearance beneath vehicle.
4. Locate transmission oil cooler assembly mounted in front lower section of vehicle, typically ahead of or integrated with radiator assembly.
5. Place large drain pan beneath transmission pan drain plug location and secondary pan beneath cooler area.

Procedure

1. 1

   Disconnect battery negative terminal
   Disconnect the negative battery terminal to prevent electrical system activation during the procedure. The battery is located in the trunk. Use a 10mm socket to loosen the negative terminal clamp and secure the cable away from the battery post.
2. 2

   Drain partial transmission fluid
   A full transaxle pan drain is NOT required to replace the front-mounted transmission oil cooler. Fluid loss occurs only when the cooler lines are disconnected. Verify the ZF 6HP26 transaxle pan/level plug location against factory documentation, but plan to capture only residual fluid from the cooler lines rather than draining the transaxle pan. Position drain pan beneath the plug. Remove the drain plug and allow fluid to drain into the pan. Note: the exact drain procedure and fluid quantity must be verified against the ZF 6HP26 service manual. This will reduce fluid loss when disconnecting cooler lines. Reinstall drain plug hand-tight for now (will be torqued during refill). Note: Locate the transmission fluid drain/level plug on the ZF 6HP26 transmission pan (DB9 uses the ZF 6-speed automatic). Position drain pan beneath plug. Remove the plug and allow fluid to drain. Note: this transmission uses a fill-from-bottom level-set procedure rather than a dipstick — verify the correct drain and fill plug locations in factory documentation before proceeding. Note: The 2009 DB9 uses a rear-mounted ZF 6HP26 transaxle with a sealed pan assembly. A full transaxle drain is NOT required to replace the front-mounted cooler; fluid loss occurs only when the cooler lines are disconnected. Verify whether a pan/overflow drain plug is present before attempting any drain, and plan to capture residual fluid from the cooler lines rather than draining the transaxle pan.
3. 3

   Remove front undertray panels
   Remove the front undertray panels to access the transmission oil cooler. Remove the Torx fasteners securing the undertray sections. The DB9 typically uses multiple undertray panels with T25 and T30 Torx fasteners. Work from rear to front, supporting each panel section as the last fasteners are removed. Set panels and fasteners aside in organized manner.
4. 4

   Access transmission oil cooler assembly
   Locate the transmission oil cooler mounted in the front lower section, typically integrated with or positioned near the main radiator and A/C condenser assembly. Identify the two transmission cooler lines (supply and return) connecting to the cooler. These are typically quick-disconnect or threaded fittings with protective caps or boots.
5. 5

   Disconnect transmission cooler supply line
   Cover the supply line connection point with a shop towel to catch residual fluid spray. If equipped with quick-disconnect fittings, use the appropriate transmission line disconnect tool to release the locking mechanism and pull the line free. If threaded fittings are present, use a flare wrench to avoid damaging the fitting. Allow residual fluid to drain into catch basin. Inspect the O-ring on the line end and replace if damaged.
6. 6

   Disconnect transmission cooler return line
   Repeat the disconnection process for the return line using the same technique as the supply line. Cover connection with shop towel, release the fitting, and allow fluid to drain. Cap or plug both disconnected lines with clean shop towels or plastic caps to prevent contamination and further fluid loss.
7. 7

   Remove cooler mounting fasteners
   Locate and remove the mounting fasteners securing the transmission oil cooler to its bracket or frame mounting points. The number and type of mounting fasteners securing the cooler assembly must be verified against factory documentation for the 2009 DB9 before beginning. Do not assume a count. Support the cooler assembly with one hand while removing the final fasteners to prevent it from falling. Note: The transmission oil cooler is secured by mounting fasteners whose exact count and type must be verified against 2009 DB9 service documentation before proceeding. Note: Remove the cooler assembly mounting fasteners (count and type to be verified against Aston Martin DB9 workshop documentation). Support the cooler assembly with one hand while removing the final fasteners to prevent it from falling.
8. 8

   Remove transmission oil cooler assembly
   Carefully lower the transmission oil cooler from its mounting position. Tilt the cooler to drain any remaining ATF into the drain pan. Inspect the cooler for signs of external damage, leaks, or debris. Check mounting brackets for cracks or wear. If cooler showed signs of internal blockage or contamination, inspect transmission fluid for debris and consider transmission filter service.
9. 9

   Prepare new transmission oil cooler
   Unpack the new transmission oil cooler and verify it matches the original unit in physical dimensions, port locations, and mounting points. Install new O-rings on both cooler ports, lubricating them lightly with clean ATF. Verify all mounting hardware is present. If original mounting brackets or rubber isolators are reusable and in good condition, transfer them to the new cooler.
10. 10

    Install new transmission oil cooler
    Position the new transmission oil cooler into the mounting location, aligning mounting holes with frame or bracket mounting points. Install mounting fasteners hand-tight initially. Verify cooler is properly seated and ports are oriented correctly for line connections. Tighten mounting fasteners in a cross pattern to ensure even seating. Torque mounting fasteners to the factory-documented specification for the 2009 DB9 transmission oil cooler (value must be confirmed before assembly). Note: Torque mounting fasteners to the manufacturer specification (verify exact value against 2009 DB9 service documentation before final tightening). Note: Torque mounting fasteners to Aston Martin DB9 specification (value to be verified against official workshop documentation before final tightening).
11. 11

    Reconnect transmission cooler lines
    Remove protective caps from transmission cooler lines. Inspect line ends and install new O-rings on both supply and return lines, lubricating with clean ATF. Connect the supply line to the appropriate cooler port (typically marked or identified by position). For quick-disconnect fittings, push firmly until an audible click confirms engagement. For threaded fittings, hand-tighten then snug with flare wrench. Repeat for return line. Verify both connections are secure by attempting to pull lines free.
12. 12

    Reinstall front undertray panels
    Reinstall the front undertray panels in reverse order of removal. Align each panel section with its mounting points and install Torx fasteners, working from front to rear. Tighten fasteners in a progressive pattern to avoid warping panels. Ensure all fasteners are secure but do not overtighten plastic mounting points.
13. 13

    Refill transmission fluid
    Access the transmission fill plug located on the side of the ZF 6HP26 transmission pan. This transmission has no dipstick; fluid level is set via the overflow standpipe at a specified fluid temperature. Using a transmission funnel with long neck, add the ZF-specified ATF for the 6HP26 transmission (ZF Lifeguard 6 / Shell M-1375.4 equivalent) — verify the exact approved specification against Aston Martin documentation. Begin by adding fluid to replace only the amount lost at the cooler lines during the procedure, then set the final level via the overflow method. Start engine and allow to idle in Park. Check fluid level using the overflow/level plug while the transmission is at the ZF-specified fluid temperature. This transmission has no dipstick. Add fluid until it begins to seep from the open level/overflow plug with the transmission at the specified fluid temperature, then install the plug. There is no dipstick or MIN/MAX mark on this sealed transmission. Total system capacity must be verified against ZF/Aston Martin documentation (approximately 9-10 liters dry fill); only add what was lost during the procedure. Note: ZF Lifeguard 6 ATF (Aston Martin-approved spec for the ZF 6HP26) Note: The ZF 6HP26 in this DB9 is a sealed transmission with no dipstick; it must be filled from the bottom level plug. With the vehicle level, add fluid through the fill/level plug until fluid runs out, then start the engine and bring the transmission to the specified fluid check temperature for the ZF 6HP26 level-set procedure (verify exact temperature window against ZF/Aston Martin documentation before setting the level). Top up through the level plug until fluid just begins to overflow, then install the plug. Use ZF-specified Lifeguard 6 ATF (Aston Martin spec). Note: The DB9 ZF 6HP26 transaxle is a sealed unit with NO dipstick; fluid level is set via the fill/overflow plug on the pan at a specified fluid temperature. Using a pump/long-neck funnel, add Aston Martin-approved ZF Lifeguard 6 full-synthetic ATF through the fill plug. Add fluid to replace only what was lost during the procedure, then bring the transaxle to the specified fluid temperature and set the level per the overflow-plug method (allowing excess to drain until a steady trickle is reached). Confirm the correct fill temperature and exact fluid specification against Aston Martin workshop documentation. Note: "name": "ZF Lifeguard 6 full-synthetic ATF (Aston Martin-approved, 6HP26)", "quantityQuarts": 9.5 Note: add Aston Martin-approved ZF Lifeguard 6 full-synthetic ATF (6HP26 specification) Note: Transmission fluid level must be set at the ZF-specified fluid temperature for the overflow procedure (commonly in the 30-40°C range for the 6HP26 — verify exact spec against ZF/Aston Martin documentation). Checking at the wrong temperature will cause an incorrect fill level.
    ⚠Transmission fluid level must be checked with transmission at operating temperature (approximately 80-90°C / 176-194°F). Cold level readings will be inaccurate.
14. 14

    Reconnect battery and clear fault codes
    Reconnect the negative battery terminal in the trunk and tighten the clamp securely. If the vehicle is equipped with a diagnostic port scanner, connect it and clear any transmission-related fault codes that may have been triggered during the procedure. If no scanner is available, the codes may self-clear after several drive cycles.
15. 15

    Pressure test and leak inspection
    Lower vehicle to ground. Start engine and allow to idle for 5 minutes while monitoring for leaks around cooler connections and mounting area. Shift transmission through all gear positions (P-R-N-D-manual modes) while stationary with brake applied, pausing 5 seconds in each position. This circulates fluid through the cooler and pressurizes all connections. Return to Park and inspect all connection points for seepage. Raise vehicle and perform final inspection of cooler area and undertray for any fluid drips.

Reassembly

1. Ensure all transmission cooler line connections are fully seated and locked into place before operating vehicle.
2. Verify transmission fluid level is correct when transmission reaches full operating temperature.
3. All undertray panels must be properly secured to prevent aerodynamic issues and component damage.

Verification

• Start engine and verify no transmission fluid leaks are present at cooler connections or mounting points after 5-minute warm-up period.
• Test drive vehicle through multiple transmission gear changes and verify smooth shifting with no slipping or delayed engagement.
• After test drive, recheck transmission fluid level with transmission at operating temperature and top off if necessary.
• Verify transmission temperature gauge reads normal operating range (if equipped) or use scan tool to confirm transmission temperature is within normal parameters (80-90°C / 176-194°F).
• Perform final inspection of cooler area and undertray for any signs of fluid seepage after 24 hours of normal driving.

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