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Knock Sensor

The “check engine” light has recently been going on & off. The Autozone diagnostic tool says it’s the “knock sensor.” How important is it to get this replaced? Are there ways for me to maintain my car without replacing this sensor? Also, I’m going to be driving from Colorado to West Virginia in a couple of weeks. Thanks.


It’s only important if you don’t want to destroy your engine. Use the highest octane gas you can get and drive very gently until you fix this. Note that removing, cleaning, and replacing the sensor might fix it.

You should not rely on a diagnosis from AutoZone. Their job is to scan the car and provide the codes to you; not diagnose a problem. A code is only a starting point.

What code(s) did they give you? A knock sensor code may not necessarily mean a faulty knock sensor.
A knock sensor provides a signal to the ECM (computer) to retard the ignition timing when a pre-ignition rattle exists. If the situation is bad enough the ECM may not be able to retard the timing enough to offset the problem.

The EGR system is always suspect in a case like this and if you hear any rattling on acceleration then this problem really needs to delved into.

“How important is it to get this replaced?”

A few thousand miles from now, when you need to have the engine torn down in order to replace damaged valves and pistons to the tune of…maybe $1,200…you will wish that you had not hesitated to replace the knock sensor. If it wasn’t necessary, Subaru would not have spent the money to equip the engine with one.

A few months from now, you will probably wish that you had paid your mechanic $150 or so to replace the knock sensor.

In addition to what others have said, you will probably get lousy performance and reduced fuel economy until it’s replaced.

Are there ways for me to maintain my car without replacing this sensor?

You seem to be asking if there is some way to maintain your car without doing any maintenance. If that’s your question, the answer is “no”.