Knock sensor tip

subaru
engines
lights
outback
sensors

#1

Hey, all.

Here is something to check on knock sensor repairs.

Not asking for advice, just throwing this one out there for everyone else

I had a check engine light come on my car in the middle of a trip. Power dropped, but not TOO badly. I got home without anything severe happening.

Later in the same day, I took it to get the codes read. The machine spat out a P0325, Engine Knock Sensor Error.

Long story short. The knock sensor tested fine, but there was junk/scale on the bottom of it that had caused a high resistance in the electrical circuit. I removed the scale on the sensor, scuffed up the mounting surface on the engine block, squirted some dielectric grease on it, and put it back together. It ran just fine, with no further lights. Saved a hundred dollar part.


#2

I’ll just add this: It’s quite common to find problems like this. The automotive industry spends untold millions of dollars to develop these systems but usually intalls $2 parts such as sensors, relays and the like on the vehicle. They buy these parts from other manufacturers and usually at the lowest bid. It’s no wonder that a lot of these high dollar engineered automotive systems are installed down the line seemingly as an afterthought. Toyota knows all about this scenario all too well. A quality system should include quality parts.


#3

It’s a corrosion issue, nothing else. The car is 11 years old with 150,000 miles on it. That part has not needed a bit of service before this, and none of the other sensors have needed any attention, either. That’s pretty darn good, especially since the O2 sensors should have crapped out 80,000 miles ago. Stuff is GOING to go bad in that amount of time. And if the only problem is a high resitance to ground tripping the computer to make a warning light come on, then I’m not bothered.


#4

The knock sensor trouble mentioned is fairly common to Subarus. The sensors are also prone to cracking due to the heat they are subjected to and sometimes need to be replaced.


#5

And that’s true with many things.
A good cleaning would solve the problem.
But most people just don’t do that any more.
Investing all that labor time on the chance that cleaning might work is quite a gamble when paying a shop to do it with the chance the cleaning might only work for a short while…then need to pay again to finally replace it after all.


#6

I was not referring to your vehicle at all since you did not list the year or mileage. This just reminded me that in my immediate family we have several vehicle that are from 1 year to 5 years old. There has been a plethora of failures that related to 02 sensors, door lock switches, ABS sensors, gas caps and radiator caps, wiper fluid motors, air pressure monitoring sensors and others. The vehicles all run fine and range from Fords to BMWs but they have had a lot of little irritating failures. I think “attention to detail” is missing in a lot of newer vehicle parts especially when it comes to electronics. This may be an isolated problem but I don’t think so.