NOX sensor replacement

[Zeppo]

My daughter is driving across a few states today coming back from a trip in
her 2001 Forester and her check engine light came on. At the last gas stop
before it came on she noticed her gas mileage was down about 30%. She
stopped at a mechanic who read the code and said she needed a NOX sensor. He
said she would be OK finishing the trip before having it done. She was an
hour from home then.

Where is the NOX sensor located? Is it easily accessible? What should it
cost to replace?

She had a new cat put in last October. Would they have replaced the sensor
then?
Jon

 

[S]

Hi Jon!

My daughter is driving across a few states today coming back from a trip in
her 2001 Forester and her check engine light came on. At the last gas stop
before it came on she noticed her gas mileage was down about 30%. She
stopped at a mechanic who read the code and said she needed a NOX sensor. He
said she would be OK finishing the trip before having it done. She was an
hour from home then.

Where is the NOX sensor located? Is it easily accessible? What should it
cost to replace?

She had a new cat put in last October. Would they have replaced the sensor
then?
Jon

There is a _knock_ sensor. These do fail, and are easily replaced.
Then there is an Oxygen sensor. These can go bad as well, and are a
little harder to get to.

I don't think there is a Nitric Oxide (NOx) sensor.

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[Zeppo]

Hi Jon!



There is a _knock_ sensor. These do fail, and are easily replaced.
Then there is an Oxygen sensor. These can go bad as well, and are a
little harder to get to.

I don't think there is a Nitric Oxide (NOx) sensor.

ByeBye! S.

Steve Jernigan KG0MB

Thanks for the reply Steve. I checked with my daughter, and it is the knock
sensor that needs replacement. That actually makes a lot more sense as it
would directly affect gas mileage. Any idea where it is located?

Thanks,
Jon

 

[clare]

Thanks for the reply Steve. I checked with my daughter, and it is the knock
sensor that needs replacement. That actually makes a lot more sense as it
would directly affect gas mileage. Any idea where it is located?

Thanks,
Jon

Not 100% sure, but usually on the top of the motor towars the back -
it threads into the block. Generally not hard to change once you get
down to it.

 

[johninky]

This link may help.



http://www.lovehorsepower.com/SubaruDocs/subaru_legacy_knock_sensor.htm

 

[S]

Hi again, Jon!

Thanks for the reply Steve. I checked with my daughter, and it is the knock
sensor that needs replacement. That actually makes a lot more sense as it
would directly affect gas mileage. Any idea where it is located?

You bet.
As Clare says, it is bolted to the top of the engine block., toward
the back, just to the left (drivers side) of, and below the throttle
body.
Look for a round black plastic thingie about 1.5 inches in diameter by
1 inch tall, with a single lead (two wire), and a bolt thru the middle
holding it to the block. Think it's an 8mm bolt; 12mm head in any
event.

It's a little busy in that area with the cables for the throttle and
some misc. wiring, but once you get your eyes to focus on it (bright
light helps immensely), it isn't any trouble to put a 12mm socket on
the end of a 4 - 6 inch extension on it.

Remove the bolt, and disconnect the lead, either at the sensor, or at
the connector into the engine harness. I'm trying to remember what the
connectors look like; I think you will want an ice pick or similar to
lift either a plastic tab, or a wire retainer. This turns out to be
the hardest part of the project, 'cause it's kinda tough to get both
hands on the job.

I think these are fairly expensive at the dealership, but probably
about $30 at a salvage yard. There is a way to test them with an
ohmmeter. I can't recall exactly, but the folks at the yard should
know. Perhaps someone here can tell us as well?

Anyway, be sure the replacement is clean and free of corrosion where
it hits the engine block, and also that the block is clean. Connect
the lead, put a dab of antisieze on the bolt, and bolt it down using
only modest torque; 10 - 15ft.lb or so.

It might take a little while running for the CEL to go away, or you
could reset the ECU by disconnecting the negative battery terminal for
several minutes, or use an OBDII reader to reset the code.

FWIW, this is a fairly common problem, and it will cause your fuel
economy to drop.

Pardon any typos that sneak in; our kitten has been "helping" me type
this morning Hope this helps.

ByeBye! S.
Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[Zeppo]

Hi again, Jon!



You bet.
As Clare says, it is bolted to the top of the engine block., toward
the back, just to the left (drivers side) of, and below the throttle
body.
Look for a round black plastic thingie about 1.5 inches in diameter by
1 inch tall, with a single lead (two wire), and a bolt thru the middle
holding it to the block. Think it's an 8mm bolt; 12mm head in any
event.

It's a little busy in that area with the cables for the throttle and
some misc. wiring, but once you get your eyes to focus on it (bright
light helps immensely), it isn't any trouble to put a 12mm socket on
the end of a 4 - 6 inch extension on it.

Remove the bolt, and disconnect the lead, either at the sensor, or at
the connector into the engine harness. I'm trying to remember what the
connectors look like; I think you will want an ice pick or similar to
lift either a plastic tab, or a wire retainer. This turns out to be
the hardest part of the project, 'cause it's kinda tough to get both
hands on the job.

I think these are fairly expensive at the dealership, but probably
about $30 at a salvage yard. There is a way to test them with an
ohmmeter. I can't recall exactly, but the folks at the yard should
know. Perhaps someone here can tell us as well?

Anyway, be sure the replacement is clean and free of corrosion where
it hits the engine block, and also that the block is clean. Connect
the lead, put a dab of antisieze on the bolt, and bolt it down using
only modest torque; 10 - 15ft.lb or so.

It might take a little while running for the CEL to go away, or you
could reset the ECU by disconnecting the negative battery terminal for
several minutes, or use an OBDII reader to reset the code.

FWIW, this is a fairly common problem, and it will cause your fuel
economy to drop.

Pardon any typos that sneak in; our kitten has been "helping" me type
this morning Hope this helps.

Thanks Steve and Johninky,
She's bringing in the car tomorrow and I'm picking up the part in a little
bit.

Jon

 

[Zeppo]

Thanks Steve and Johninky,
She's bringing in the car tomorrow and I'm picking up the part in a little
bit.

Jon

Sorry to not report back sooner...

Knock Sensor replaced. CEL is gone, mileage back to normal. Job was fairly
simple but I had to pick up a new torque wrench in the middle of it the job
as mine had mysteriously gone missing.

Thanks for the knowledge, links and advice.
Jon

Thanks for the advice and

 

[S]

Hi Jon!

Knock Sensor replaced. CEL is gone, mileage back to normal. Job was fairly
simple but I had to pick up a new torque wrench in the middle of it the job
as mine had mysteriously gone missing.

Thanks for the knowledge, links and advice.
Jon

You are most welcome. Free advice, and worth every penny ;-)

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101