Detonation sensor - Knock

Detonation sensor - Knock

Although the knock sensor is not as well known as some of its counterparts, it is essential to keep your car's engine running properly. It informs you when detonation or pre-ignition is present.

What is a detonation sensor?

Engine detonation is usually caused by harmful forms of abnormal combustion, such as pre-ignition . 

The detonation sensor, located on the outside of the engine block, registers detonation noise in all engine operating states to prevent engine damage. In other words, it listens for vibrations sustained by the engine block structure.

Why are these vibration detection sensors important?

The detonation sensor is necessary because - although loud bangs and pings are heard by humans, the sensor detects imperceptible noises. 

So when the sensor detects any high-frequency engine vibration characteristic of knocking noise, it sends a voltage signal to the electronic control unit (ECU) and this delays spark plug timing. As a result, a knock sensor can reduce fuel consumption, help improve fuel economy and increase torque.

What are the signs of a faulty detonation sensor?

Detonation sensor failure can easily cause one or more visible symptoms. 

The most common sensor problems include:

1. A check engine light on

When the Powertrain Control Module (PCM) detects a detonation sensor or faulty circuit, it will illuminate the engine check LED and trigger a corresponding Diagnostic Trouble Code ( DTC ).

2. A pinging noise from the engine

In the event of a detonation sensor failure, the PCM may not be able to recognise or repair the detonation. The faulty sensor may result in a metallic noise from the engine. 

You will also notice that the noise becomes most prominent when the engine is under a high load.

3. Poor engine performance

A fault in the detonation sensor can cause the PCM to misadjust the ignition timing, resulting in inadequate engine performance.

The engine may not feel right while driving at high speed or when the vehicle is carrying a light or heavy load.

In such a case, it should be checked by a mechanic even if the check engine light is not on.

3. Poor acceleration

A faulty ignition sensor may not let the engine accelerate correctly while driving on the motorway, causing the car to lose fuel consumption. 

4. Loss of power

Once the engine control unit realises that the knock sensor is not working properly, the car will most likely lose power. 

The amount of power lost will depend on the octane limit of the engine and how much it depends on the detonation sensor input. 

The cars with the highest power loss are high compression and flexible fuel engines. This is because power loss slows timing and keeps the transmission away from the unit until the knock sensor is replaced. 

What causes a detonation error?

There are several reasons why an engine detonation happens. 

Here are some potential causes:

⦁ Spark ignition does not occur in time

⦁ Improper air/fuel mixture ratio

⦁ Deposits inside the cylinder (dirt and contaminants entering the cylinder)

Defective spark plugs

⦁ Spark plugs that are of the wrong type or with deposit build-up

⦁ Low octane fuel

⦁ Incorrect mounting of detonation sensors

⦁ Mechanical damage

⦁ Abnormally high engine operating temperatures

⦁ Carbon accumulation inside the combustion chamber(s)