Audi Audi A6 2011-2018 Emissions & Sensor Bolt Torque Specifications

Using the correct torque is crucial for proper sensor function and preventing leaks. Over-tightening can damage the sensor or its threads, leading to inaccurate readings or sensor failure. Under-tightening can result in leaks, which could lead to incorrect emission readings, triggering fault codes, and potential exhaust leaks. For example, an overly tightened oxygen sensor might fracture its ceramic element leading to replacement.

Over-tightening can damage the sensor body, threads in the exhaust manifold, or other mounting points. This can lead to stripping threads, cracking the sensor housing, or distorting the sensor itself, impacting its accuracy. In extreme cases, over-torquing can result in complete sensor failure, requiring costly repairs. A common example is stripping the threads of the lambda sensor bung in the exhaust manifold, requiring retapping or replacement of the manifold.

Under-tightening can result in leaks of exhaust gases, which may be hazardous and also lead to incorrect readings. A loose sensor can also vibrate and fail prematurely. For instance, a NOx sensor improperly tightened can leak, causing a false 'lean' reading and triggering a check engine light. This can also cause exhaust fumes to enter the passenger compartment.

It's generally recommended to use a small amount of anti-seize compound on the threads of emissions sensor bolts, especially those located in high-heat environments such as exhaust manifolds. This will prevent them from seizing and make future removal easier. However, avoid applying anti-seize directly on the sensor itself, particularly on the sensing element. Use a copper-based anti-seize to ensure good conductivity and prevent corrosion.

Emissions sensors typically don't require routine torque checks unless they have been recently removed and reinstalled. However, if you've noticed exhaust leaks or have recently done any work in the vicinity of the emissions sensors, it's good practice to ensure they are tightened to the proper torque specifications using a calibrated torque wrench. Consider checking after any significant engine vibration events or off-road driving.