The check engine light came on and the code came up as the knock sensor. We will make an appointment to get it replaced, but is it ok to drive for a week or two? This would include a 3 hour mostly highway trip. Thanks in advance!!!

 

Shouldn't be any problem at all.  But the car will run slightly better and more efficiently when you do replace it. (Someone correct me if I'm wrong here!!!) 

Not a major problem. Just be aware that motor will feel like it is down 25 horse power, and gas millage will be off about 5 mpg. The computer reacts to the bad knock sensor by retarding engine timing electronically.

generally not a big deal.

 

but they can vary as to how bad they are and cause a large decrease in power if bad enough.  but that's not the norm.

 

the knock sensors are like $10 on ebay, require removing one 12mm bolt, and takes about 15 minutes.  easy peasy to replace.

Two questions on knock sensor.  1.  Anyone know where I can find a DIY guide to replace it?

 

2/  If the OBD reads P0328 for knock sensor is it likely to be just a bad sensor or caused by something else?

Knock sensor 101

http://www.ultimatesubaru.org/forum/topic/116520-knock-sensor-101-and-replacement/

 

P0328 Knock sensor High input. Most likely to be the sensor itself or a poor ground for the sensor. The sensor grounds to the block, so make sure the mounting spot on the block is clean of dirt and corrosion.

If you have a multimeter you can check voltage at the sensor wire by back probing the connector. Voltage higher than 2.5v means there is poor continuity through the sensor or a bad ground.

When I just did mine, the readings were: Signal wire was around 4.8v with the sensor disconnected and key on. With sensor connected and grounded through the center bolt, that voltage dropped to around 2.3v with either key on or running. Sensor should be reading around 0.553 m ohms +/- resistance. So if you suspect your sensor is bad, check the resistance first with it unplugged. If you see an open circuit, it's bad. If it's still showing a value, try moving the wire around and see if it drops out or fluctuates.

 

As Fairtax mentioned, the surface MUST be clean. I had to go back and remove it and took a chisel to knock down a rust lip that formed around the original sensor location, that the new one seemed to be touching. Also had some gunk mysteriously get between and that needed wiped off again. Don't forget to pull the battery NEG cable to rest the code. If you start the engine and the CEL immediately reappears, go back and check the surface again between the sensor and the block. Do NOT over-tighten.

code is usually the sensor - they often crack at the base, but can still look fine and be bad.  it's the most common sensor failure on Subaru's by a long shot.

 

$10 or less on ebay.

 

it's one 12mm bolt to remove it - you hardly need instructions, but use this as a chance to get a free FSM availble all over the internet.

the directions are posted online in various places too.  same basic procedure for like 20 years on legacy/impreza/outback/foresters.

Edited October 21, 201510 yr by grossgary

code is usually the sensor - they often crack at the base, but can still look fine and be bad.  it's the most common sensor failure on Subaru's by a long shot.

 

$10 or less on ebay.

 

it's one 12mm bolt to remove it - you hardly need instructions, but use this as a chance to get a free FSM availble all over the internet.

the directions are posted online in various places too.  same basic procedure for like 20 years on legacy/impreza/outback

 

Thanks for the reply.  FSM?? Is that for Forester Service Manual maybe?

FSM generally means "Factory Service Manual" around here. And whenever someone is wondering about changing their knock sensor I like to offer up my video of the process. I'm no hotshot mechanic and I found it easy enough:

I got a P0328 code a couple of weeks ago.  Reset it and it came back after a few days.  I was going on a 1500 mile trip so I ordered a cheap after market knock sensor for all of $12.  It just takes a few minutes to install on my 2000 OBW.

 

Just got back from the trip.  I had no check engine light and my mileage went from 25 MPG or so to nearly 28 MPG.  Wow!!  Could this be attributed to the knock sensor?  I had 4 fill-ups so it would seem to not be just chance.

 

Before changing the knock sensor there was no noticeable knock or lack of power.

When the ECU detected a knock or isn't getting a signal from the knock sensor it retards the timing a bit and adds more fuel to the engine to keep it cooler to prevent a cylinder from overheating.

So yes. A knock sensor code will definitely drop the fuel economy by 3 mpg

Edited October 3, 20169 yr by golucky66

Thanks,  hope it stays getting this better mileage!