* Poor Engine Performance: The engine's computer (ECU) relies on the knock sensor to detect detonation (uncontrolled explosion of the air/fuel mixture). A faulty sensor might report no knock even when it's happening, or falsely report knock when it isn't. This leads to the ECU making incorrect adjustments to the ignition timing. The result can be sluggish acceleration, poor fuel economy, and a rough-running engine.
* Reduced Engine Power: To protect the engine from damage due to detonation, the ECU will often retard (delay) the ignition timing significantly if it *thinks* it detects knock. Even a false positive from a bad knock sensor can cause a significant reduction in engine power.
* Engine Damage: Continued detonation from unchecked knock (due to a faulty or absent sensor) will eventually cause damage to internal engine components. This includes:
* Piston damage: Detonation creates extremely high pressures that can damage or even shatter pistons.
* Connecting rod damage: The intense forces can bend or break connecting rods.
* Crankshaft damage: The crankshaft can also be damaged by the excessive forces.
* Head gasket failure: The high pressure can blow a head gasket.
* Cylinder wall scoring: The pistons can score the cylinder walls.
* Catalyst damage (catalytic converter): Unburnt fuel from poor combustion caused by incorrect timing can damage the catalytic converter.
In short, ignoring a bad knock sensor can lead to costly engine repairs or even a complete engine rebuild. It's a relatively inexpensive sensor to replace, so it's best to address the problem promptly.
