Transmission Speed Sensor - Output

Replace the transmission output speed sensor on the ZF 6-speed automatic transmission, located on the transmission housing near the output shaft.

Warnings

Tools required

Parts

• Transmission output speed sensor × 1 — Use OEM Aston Martin or ZF specification
• O-ring seal for speed sensor × 1 — Usually included with sensor

Fluids

• Touchtronic 6-speed ZF ATF — 1.5 qt

Preparation

1. Park vehicle on level ground and engage parking brake
2. Disconnect negative battery terminal to prevent fault code generation during sensor disconnection
3. Allow transmission and exhaust system to cool completely (minimum 1 hour after operation)
4. Raise vehicle on lift or secure on jack stands at all four corners, ensuring vehicle is level for proper fluid fill procedure
5. Remove engine undertray panels using Torx fasteners to access transmission from below

Procedure

1. 1

   Locate the transmission output speed sensor
   Note: On the ZF 6HP26 used in the 2009 DB9, the output/turbine speed sensors are integrated into the internal mechatronic unit and are not externally serviceable threaded components. Verify against Aston Martin service documentation whether an externally accessible output speed sensor exists before proceeding; access may require dropping the transmission pan and servicing the mechatronic/sensor assembly rather than unthreading an external sensor. The sensor is a cylindrical component with an electrical connector on top and threads into the transmission case. Note: On the DB9 the ZF 6HP26 is configured as a rear-mounted transaxle. Be aware that on the 6HP26 the output/turbine speed sensors are part of the internal mechatronic unit and are generally NOT externally serviceable. Per Aston Martin service documentation, confirm whether any externally accessible output speed sensor exists for this transmission before proceeding; if not, servicing requires dropping the transmission pan and accessing the mechatronic/sensor assembly.
2. 2

   Disconnect the sensor electrical connector
   Press the locking tab on the electrical connector and carefully pull the connector away from the output speed sensor. Note the routing of the wiring harness for reinstallation. If the connector is difficult to access, trace the harness to identify any clips or ties that need to be released for additional slack. Note: Disconnect the negative battery terminal (battery is located in the luggage compartment/boot on the DB9) to prevent fault code generation during sensor disconnection. Note that a battery disconnect may trigger module re-initialization requirements.
3. 3

   Position drain pan and prepare for fluid loss
   Place a drain pan beneath the output speed sensor location. A small amount of transmission fluid may drain from the sensor bore when removed. Have shop towels ready to manage fluid flow. Have shop towels ready to manage fluid flow.
4. 4

   Remove the output speed sensor
   Confirm the sensor retention method against factory documentation. If the sensor is retained by a hold-down bolt, remove that bolt and withdraw the sensor straight out; if it is threaded into the case, loosen by turning counterclockwise with the correct socket. Once threads are clear, quickly withdraw the sensor and allow residual fluid to drain into the pan. Inspect the sensor o-ring seal on the removed sensor. Note: unknown — verify retention method (threaded sensor vs. single-bolt retained) and exact tool size against Aston Martin/ZF documentation before removal Note: Verify the sensor mounting method against Aston Martin/ZF documentation. If the sensor is externally threaded, it is almost certainly a standard right-hand thread; remove it by turning counterclockwise. Verify thread type against Aston Martin/ZF documentation before applying force. If the output speed sensor is part of the internal mechatronic unit, the transmission pan and mechatronic assembly must be serviced instead of unscrewing an external sensor. Note: Tool size not verified — confirm the exact socket/Torx size (if an external sensor exists) against Aston Martin/ZF documentation before removal.
5. 5

   Clean the sensor mounting bore
   Using shop towels, clean the sensor mounting bore in the transmission case thoroughly. Remove any debris, old seal material, or metal particles. Inspect the bore threads for damage or debris that could prevent proper sealing.
6. 6

   Inspect the new sensor and prepare for installation
   Verify the new output speed sensor matches the original in connector type and physical dimensions. Ensure the o-ring seal is properly seated in the sensor groove. Lightly lubricate the o-ring with clean ATF to aid installation and prevent seal damage.
7. 7

   Install the new output speed sensor
   Thread the new sensor into the transmission case by hand, turning clockwise until finger-tight. Ensure the sensor threads smoothly without cross-threading. Once hand-tight, use a socket or wrench to snug the sensor securely. Do not overtighten as this can damage the aluminum transmission case or crush the o-ring seal. Note: Torque unknown — obtain the exact factory specification for the sensor (or its retaining bolt) from Aston Martin/ZF documentation before final tightening. Note: Torque specification not verified — obtain the exact factory spec from Aston Martin/ZF documentation before final tightening. Do not rely on an estimated value.
8. 8

   Reconnect the electrical connector
   Push the electrical connector onto the new sensor until the locking tab clicks into place. Gently tug on the connector to verify it is secure. Route the wiring harness as originally positioned and secure any clips or ties that were released.
9. 9

   Refill the transmission with ATF
   Locate the transmission fill plug on the side of the transmission case. Remove the fill plug and use a fluid pump or transmission fill equipment to add ZF-specification ATF (ZF Lifeguardfluid 6) to replace the fluid lost during sensor removal. Add fluid only to replace the small amount lost during sensor removal (typically a few ounces), then check fluid level according to manufacturer procedure. The transmission fluid must be within the ZF-specified check temperature window (approximately 30-40°C / 86-104°F) for accurate level checking; checking above this range will give a false-low reading and lead to overfilling. Note: Locate the transmission fill plug on the side of the transmission case. Remove the fill plug and use a fluid pump or transmission fill equipment to add the ZF-specified ATF (ZF Lifeguard 6 / ZF S671.090.255 or Aston Martin-approved equivalent for the ZF 6HP26 transmission) to replace the fluid lost during sensor removal. Add fluid only to replace the small amount lost during sensor removal (typically a few ounces), then check fluid level according to manufacturer procedure. The transmission fluid must be within the ZF-specified check temperature window (approximately 30-40°C / 86-104°F per ZF 6HP26 spec) for accurate level checking — this is a controlled check window, not full operating temperature. Note: Locate the transmission fill/level plug on the side of the transmission case. Remove the fill plug and use a fluid pump or transmission fill equipment to add the correct ZF-specification ATF (ZF Lifeguardfluid 6, as specified for the 6HP26 'Touchtronic 2' transmission) to replace the fluid lost during sensor removal. Add only the amount needed to restore the correct level, checking fluid level according to Aston Martin procedure. The transmission must be at the manufacturer-specified fluid temperature window for accurate level checking. Note: the ZF-approved ATF specified for the 6HP26 transmission (ZF Lifeguard 6 or Aston Martin-specified equivalent — verify exact spec against factory documentation)
10. 10

    Verify proper fluid level
    With the transmission fluid within the ZF-specified check temperature window (approximately 30-40°C / 86-104°F) and the vehicle level, check the fluid level per Aston Martin specification. Fluid should be at the correct level when a small amount weeps from the fill/check plug hole with the engine running, the transmission fluid within the specified temperature window, and the selector position per the factory procedure. Verify exact ZF/Aston Martin level-check steps before confirming. Install the fill plug once proper level is confirmed.
11. 11

    Reinstall undertray panels
    Reinstall all engine undertray panels removed during preparation, securing with the original Torx fasteners. Ensure all panels are properly aligned and all fasteners are tightened.
12. 12

    Reconnect battery and clear fault codes
    Reconnect the negative battery terminal. Using a diagnostic scan tool compatible with Aston Martin systems, clear any stored fault codes related to the transmission speed sensor. This prevents false fault code history from affecting transmission operation.

Reassembly

1. Ensure all electrical connections are secure and properly routed
2. Verify transmission undertray panels are fully secured with all fasteners
3. Confirm transmission fluid level is correct at operating temperature before final verification

Verification

• Start the engine and allow transmission to reach operating temperature while monitoring for fluid leaks around the output speed sensor
• Using a diagnostic scan tool, verify the output speed sensor is providing valid signal readings (typically showing RPM values that correspond to wheel rotation)
• Test drive the vehicle through all gears, verifying smooth shifting and proper speedometer operation
• Check for any new transmission-related fault codes after test drive
• Perform final inspection underneath vehicle for any ATF leaks at sensor location

Related trouble codes on this vehicle

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