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Do It Yourself Auto Repair - Knock Sensor Replacement on Subaru

Updated on March 5, 2016

Knock Sensor

This old one has a crack in it.
This old one has a crack in it. | Source

Something Was Wrong

On Thursday night, I was caught in a torrential downpour. A rainstorm that had little wind, but hail and rain so heavy that 5 inches fell in a matter of hours. I was trying to drive home late at night and as I turned the corner to go up a ramp to the highway, I went through a puddle.

My car started to sputter. Then, I think it stopped. It started again when I turned the key, but there was barely enough power to go up the ramp. I definitely knew I did not want anyone behind me on the highway, so I exited at the next ramp which was, fortunately less than a quarter mile down the road.

Familiar Roads

I decided to take my time getting home, so I went on some back roads. They were not very well lit, but the stripe in the middle of the road was there, periodically, to keep me reassured that I was still on the road.

The rain was coming down so hard that it was deafening. The windshield wiper was literally smashing water back and forth.

My Daughter Had Met Me For Shopping in Town

She and I met in town. It was late. We shopped separately and went to a Thrift Store to check their book selection. She's into reading and was looking for a different book to take along on her and her husband's next road trip. Something to do.

We were hungry so we went and sat inside McDonald's for a bite to eat. Outside, there was a storm brewing. There was an odd star shaped cloud in the western sky and as we sat eating our food, it started raining and hailing.

She was glad that the car that she was driving was not her brand new car, but an older car that had some loose paint. A few hail dents weren't welcome, but it meant less damage than if she had the new car.

We Left Each Other and Drove Home Separately

She lives in a different part of the area than I do. We both live in the country. It normally takes about forty-five minutes for me to drive home from town. This night, it took a good hour and a half for me to get home.

Not only that, the rain was beating my car so hard that my windshield wiper on the driver's side was knocked loose and flew off. So, I was driving in this storm, with a car that wasn't working right and I had to lean to the passenger side of the car to see what little I could see of the road.

It wasn't fun. I would venture to say that I was too calm. I figured if I had made it as far as I had without losing complete power in my vehicle, I was doing good.

The Next Day

I had to narrow down what was wrong with the car. It started okay but it acted spongy when I stepped on the gas.

I got an oil change after work and there was a little less oil in the block than was supposed to be. That corrected some of the power issues, but it was still spongy. A coworker told me to take the car to an auto parts store and have them use their computer to check why the check engine light was on. Their machine said that I had two problems. One, a faulty knock sensor and two, my gas cap was defective.

I Ordered The Sensor

The sensor was about eighty dollars. I asked the sales clerk if it was difficult to install and the other sales clerk volunteered that I should 'youtube' the repair. He said that he looks to youtube for a lot of his auto repair work.

So, I did that. The part wasn't going to be in until the next, so I drove the car home. I had had another car shop listen to the motor run and they said to give it a few days to let it dry out.

The Next Morning

I was again driving the car to work. That morning I had forgotten to grab my cell phone, so I turned around in the road and went back home to get it. The car seemed to have a little power but then, as I turned into my driveway, I didn't know if the car was going to make it all the way to the house.

I looked at the RPM's and they were falling and barely going. Not even a full idle. I pulled the car to a stop and the car started to quit.

I switched to a different vehicle. Lucky for me we have more than one car.

That Night

That night, I picked up my part from the auto parts store and took it home. I opened the hood of my car and looked where the video said the sensor would be. There it was. It was even in a spot that was easy to get at.

I got some tools to work with. I needed a rachet wrench with an extension, since the bolt was located about 10 inches below the top of the motor. It took a 12 mm socket. I was afraid that the bolt would be hard for me to turn, but as I started to turn the rachet, I heard a squeaking sound as the screw started to turn.

There were leaves down by the part, so I put the bolt back in the hole and used the air from my air compressor to clean the leaves and sediment off the motor. Then, I unhooked the wires from the old sensor.

The Old Part

The old part was cracked and the clip that attached it to the sensor was in pieces. So, before I could just hook it up, I had to figure out how the clip wire fit in the clip. It took a few minutes to see how it fit together. There was no welding on the previous wires, so I just inserted the metal connector back inside the clip and attached it to the sensor.

It fit together. I put electrical tape on the connector and the wires to make sure they stayed together. Then, I cleaned up all the tools and removed everything of the motor. Went inside the car and started the motor.

It started!!! Not only did it start, but when I pushed on the gas, there was this satisfying roar of power instead of the familiar sponginess. Car fixed. I will get a new gas cap later. I should check and see if my check engine light is off. Nope, check engine light is still on. Plus, starting the vehicle causes my security light to flash. But, the car revs nicely.

The Two Sensors - Old and New

The new sensor.
The new sensor. | Source
The old sensor.
The old sensor. | Source

The Location


The Rachet With Extensions


Fits Better Here


Blowing Dirt Out With Air Compressor


Wire End Was Unhooked

Had to reorient the wire in the clip.
Had to reorient the wire in the clip. | Source
The old one was cracked.
The old one was cracked. | Source

How About You

Have you had to fix the knock sensor in your Subaru?

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How to Replace Sensor


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