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Knock Sensor Replacement
 
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Pelican Technical Article:

Knock Sensor Replacement

Jared Fenton

Time:

2 hours2 hrs

Tab:

$80

Talent:

***

Tools:

10mm socket and wrench

Applicable Models:

Volvo C30 T5 (2008-13)
Volvo C30 T5 R-Design (2008-13)

Parts Required:

Knock sensor

Hot Tip:

Follow the directions for installing the knock sensors to the letter

Performance Gain:

` Better running

Complementary Modification:

Clean fuel injectors

The knock sensor is an important part of the car's ignition system. It functions by detecting instances of detonation or "knocking" within the engine and sending a signal to the vehicle's computer that in turn adjusts the ignition timing and fuel injection. The knock sensor is essentially a microphone that "listens" for certain vibrations.

So what is detonation? Detonation is when combustion of the air/fuel mixture in each cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion flame front. The air/fuel mixture is only meant to be ignited by the spark plug and also when the piston is at the right point in the stroke of the engine. Any ignition outside the normal cycle creates the pinging or knocking noise you hear. Over time, the knocking creates increased heat and stress on the pistons, eventually leading to engine damage.

It sounds a bit complicated, but the knock sensors keep all of that under control. They also give you the ability to run a lower octane fuel in a pinch at the cost of engine performance.

Typically, a knock sensor fault will trigger a check engine light and a fault code. Use a diagnostic software package or the Volvo VADIS computer to read the codes. Unfortunately, replacing the knock sensors requires removing the air filter housing. See our article on Air Filter Housing Removal for more information.

When installing a new sensor, take care to align and torque the fastening bolts precisely. Failure to do so could result in a sensor not working correctly. It is also important to align the sensor so that the wiring harness does not come in contact with either of the sensor housings. A stray brush across the sensor by the wire could be read as detonation. Once installed, torque the securing bolt to 20Nm (14.75 ft/lbs.).

Shown here are the locations of the two knock sensors on the Volvo C30 (green arrows).
Figure 1

Shown here are the locations of the two knock sensors on the Volvo C30 (green arrows). It is important to note the position in which they are mounted. You'll want the new sensors aligned the same way. Now loosen and remove the two 10mm bolts holding the sensors to the engine block.

Both knock sensors use a common connector that plugs into the wiring harness shown here.
Figure 2

Both knock sensors use a common connector that plugs into the wiring harness shown here. Press the tab (green arrow) and pull the connector apart.

Now carefully guide the sensor wiring (green arrows) out from inside the engine bay.
Figure 3

Now carefully guide the sensor wiring (green arrows) out from inside the engine bay.

When fitting the new sensors (green arrow), make sure you mount them in the same position as before at the mounting holes (yellow arrow) on the engine block.
Figure 4

When fitting the new sensors (green arrow), make sure you mount them in the same position as before at the mounting holes (yellow arrow) on the engine block. Once installed, torque the securing bolt to 20Nm (14.75 ft/lbs.).



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