Knock Sensor

Replace knock sensor(s) on the M275 V12 BiTurbo engine by accessing sensors located in the engine valley between cylinder banks, requiring removal of intake manifold components.

Warnings

Tools required

Parts

• Knock sensor × 2 — A 000 905 37 00 or equivalent
• Intake manifold gasket set × 1 — Use OEM specification
• Cover gaskets if damaged × 1 — Use OEM specification

Preparation

1. Ensure engine is completely cool to the touch
2. Disconnect negative battery terminal and wait 10 minutes for system discharge
3. Remove engine cover by lifting upward from front clips
4. Use scan tool to document knock sensor fault codes and freeze frame data
5. Photograph all wiring harness routing and connection points
6. Relieve any residual fuel system pressure if fuel lines will be disturbed
7. Have clean workspace ready for intake components

Procedure

1. 1

   Remove upper intake components
   Disconnect all vacuum lines, breather hoses, and electrical connectors from the upper intake plenum. Remove air intake ducts and any decorative covers. Label each connection for reassembly. Remove mounting bolts securing upper intake sections and carefully lift components away from engine.
   Torque spec

   Mounting Bolts64 Nm (47 lb-ft)
2. 2

   Disconnect fuel system connections
   Disconnect fuel rail connectors and fuel lines from intake manifold area. Use appropriate line disconnect tools. Have shop rags ready to catch residual fuel. Cap open fuel lines to prevent contamination.
   ⚠Fuel may spray when disconnecting lines even after pressure relief. Have fire extinguisher accessible.
3. 3

   Remove intake manifold gasket bolts
   Working from outside to inside in reverse of tightening sequence, remove all intake manifold gasket bolts. Keep bolts organized by location. Note any bolt length differences. Once all gasket bolts are removed, carefully separate intake manifold from cylinder heads.
   Torque spec

   Gasket Bolts27 Nm (20 lb-ft)
4. 4

   Access engine valley
   With intake manifold removed, clean area around valley cover if present. Remove any additional covers or heat shields blocking access to engine valley where knock sensors are mounted. Remove cover bolts and lift covers to expose knock sensors mounted on engine block between cylinder banks.
   Torque spec

   Cover Bolts22 Nm (16 lb-ft)
5. 5

   Disconnect knock sensor electrical connectors
   Locate knock sensor wiring harness connectors in engine valley. Press release tabs and carefully disconnect both knock sensor connectors. Note routing of wiring harness for reinstallation. Check connectors for corrosion or damage.
   ℹ️Connectors may be brittle from heat exposure. Use gentle pressure to avoid breaking tabs.
6. 6

   Remove knock sensors
   Using appropriate socket and extension, carefully remove knock sensor mounting bolts. Note the exact positioning and orientation of each sensor. Remove sensors from engine block. Inspect mounting surfaces for damage, corrosion, or debris.
   Torque spec

   Knock Sensor20 Nm (15 lb-ft)
7. 7

   Clean mounting surfaces
   Thoroughly clean knock sensor mounting bosses on engine block using parts cleaner and clean rag. Ensure surfaces are completely free of oil, dirt, or old gasket material. Clean threads in mounting holes. Inspect for any cracks or damage to mounting area.
   ⚠Mounting surface cleanliness is critical for proper knock sensor function. Any contamination will affect sensor performance.
8. 8

   Install new knock sensors
   Install new knock sensors in correct orientation matching original position. Hand-thread sensor bolts to avoid cross-threading. Using calibrated torque wrench, tighten knock sensor bolts to exactly 20.0 Nm (15.0 lb-ft). Do not overtighten as this will damage sensors and cause false readings.
   ⚠Knock sensor torque is absolutely critical. Too tight or too loose will cause sensor malfunction and engine performance issues.
   Torque spec

   Knock Sensor20 Nm (15 lb-ft)
9. 9

   Reconnect knock sensor wiring
   Route knock sensor wiring harness along original path. Connect electrical connectors to both knock sensors ensuring positive engagement with audible click. Verify connectors are fully seated and locking tabs engaged. Secure any wiring clips or ties.
10. 10

    Reinstall valley covers
    Install new gaskets if required on valley covers. Position covers over engine valley and install cover bolts. Torque cover bolts to 22.0 Nm (16.0 lb-ft) in crossing pattern. Reinstall any heat shields removed for access.
    Torque spec

    Cover Bolts22 Nm (16 lb-ft)
11. 11

    Install intake manifold with new gaskets
    Position new intake manifold gaskets on cylinder heads. Carefully lower intake manifold into place, ensuring all alignment pins engage properly. Install gasket bolts hand-tight initially. Torque all gasket bolts to 27.0 Nm (20.0 lb-ft) in proper sequence (center outward, alternating sides).
    ⚠Follow proper torque sequence to ensure even gasket compression and prevent vacuum leaks.
    Torque spec

    Gasket Bolts27 Nm (20 lb-ft)
12. 12

    Reconnect fuel and vacuum systems
    Reconnect all fuel lines and fuel rail connections. Reconnect all vacuum lines and breather hoses according to photographs and labels from disassembly. Double-check all connections for proper seating.
13. 13

    Reinstall upper intake components
    Reinstall upper intake plenum sections and air intake ducts. Reconnect all electrical connectors and remaining vacuum connections. Install mounting bolts and torque to specification. Reinstall engine covers.
    Torque spec

    Mounting Bolts64 Nm (47 lb-ft)
14. 14

    Clear codes and verify installation
    Reconnect battery negative terminal. Using scan tool, clear all knock sensor fault codes from engine control module. Perform system test if available on scan tool. Start engine and verify smooth idle with no new fault codes.

Reassembly

1. Verify all electrical connectors are fully engaged with positive clicks
2. Confirm all vacuum lines are routed correctly and secured
3. Check for any tools or rags left in engine valley before closing up
4. Ensure all mounting bolts are torqued to proper specification
5. Verify engine covers are properly seated and secured

Verification

• Start engine and verify smooth idle with no unusual knocking sounds
• Using scan tool, verify no knock sensor fault codes present after startup
• Monitor knock sensor live data on scan tool to confirm both sensors reading normally (typically 0-5% knock retard at idle)
• Perform test drive and monitor for proper engine performance under load
• Verify no vacuum leaks by checking for smooth idle and proper fuel trims
• Recheck all connections after engine reaches operating temperature and cools down

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