Rick's Free Auto Repair Advice

Knock sensor symptoms

Knock sensor symptoms

What does a knock sensor do?

A knock sensor detects knock caused by detonation, pre-ignition, or engine mechanical problems. A knock sensor doesn’t cause any of these problems; its only job is to detect vibration caused by the pre-ignition, detonation, or mechanical problem and create a voltage that is read by the ECM.

An engine knocking sound will cause vibration which is picked up by the knock sensor and  reported to the ECM. If the voltage exceeds pre-determined levels, it will set one of the knock sensor trouble codes listed below.

P0325 Knock Sensor 1 Circuit Malfunction (Bank I or Single Sensor)
P0326 Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor)
P0327 Knock Sensor 1 Circuit Low Input (Bank I or Single Sensor)
P0328 Knock Sensor 1 Circuit High Input (Bank I or Single Sensor)
P0329 Knock Sensor 1 Circuit Intermittent (Bank 1 or Single Sensor)
P0330 Knock Sensor 2 Circuit Malfunction (Bank 2)
P0331 Knock Sensor 2 Circuit Range/Performance (Bank 2)
P0332 Knock Sensor 2 Circuit Low Input (Bank 2)
P0333 Knock Sensor 2 Circuit High Input (Bank 2)

What causes an engine knock large enough to set a knock sensor code?

Pre-ignition (PING) can cause a knock sensor code

Pre-ignition occurs when combustion starts before the spark plug has fired. When the spark plug fires and ignites the fuel, the two flame fronts collide, creating a knocking sound.

What causes pre-ignition?

• Glowing carbon buildup in the cylinder head ignites the fuel before the spark event.
• Incorrect spark plug heat range that prevents the spark plug from cooling properly—allows the spark plug to retain too much heat
• Running low octane fuel in a high compression engine that requires a high octane fuel

Detonation can cause a knock sensor code

Detonation occurs at the end of the combustion cycle when a rapid rise in heat and pressure causes pockets of unburned fuel to ignite and collide.

What causes detonation?

Fueling with low octane fuel in an engine that requires hi octane fuel

What knock sensor code symptoms would you notice?

• Knocking sound under hard acceleration
• Poor acceleration
• Poor fuel economy

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Posted on by Rick Muscoplat

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