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Old 02-19-2018, 03:18 PM   #1
Scooby Newbie
Member#: 477892
Join Date: Nov 2017
Chapter/Region: NESIC
Location: Waterbury Center, Vermont
2000 Impreza Wagon

Default How To: P0325 Code and Knock Sensor Replacment

Here is my write up on how to do a knock sensor replacement on the EJ22 motor. Also I wrote up some info on the P0325 code. This was on my 2000 Impreza Outback Sport so its the Phase 2, SOHC motor but the knock sensors (or the procedure at least) are the same throughout most of the Subaru lineup.

The knock sensor is used by the ecu to determine if the engine is knocking.
Also known as pre-ignition or detonation, knocking is a combustion event that is occurring to early in the engine's cycle. This could mean an explosion of fuel and air that can break pistons and bend connecting rods. This type of combustion event is identifiable by a certain sound frequency and this tonal event is transferred throughout the engine block, the knock sensor is a type of microphone if you will, that is mounted to the block and is looking for certain knocking frequencies. The timing of the the ignition or timing of the combustion event, is controlled by the ecu. The ecu will use the knock sensor to determine if there is any knocking and if there is, the ecu will retard or advance the ignition timing to compensate. The P0325 (Knock Sensor 1 Circuit Bank 1) code is generated by the ecu when it senses a out of range voltage or a short/open in the circuit. This code can be caused by faulty wiring (between the sensor and ecu), a bad ground between the sensor and engine, a bad ecu (rarely) or by an internally failed sensor. It is common for the plastic Subaru knock sensors housings to crack after time, exposing the internal components to moisture and debris. Typically if you have a P0325 code, it is due to a failed sensor but using a multi-meter to test the electrical resistance between certain components and wiring isn't a bad idea. The sensor itself is grounded by it's mounting bolt and by the mating mounting surface (which should be cleaned). It's signal is transferred through 1 wire that is connected to the ecu.

Tools Needed:

8" Extention
12mm Shallow or Deep Socket
10mm Wrench
3/8" Torque Wrench
Scotchbrite Pad or Sandpaper

Time Required:
(Subaru Warranty Flat-Rate Time: 0.7 hrs)
(Standard Flat Rate Time: 1.1 hrs)
Time it took me: 15 minutes

1) Disconnect the battery at the negative terminal (Use 10mm wrench)

2) Locate the sensor (Sensor is located right underneath the throttle and cruise control cables on the engine block, near where the engine and transmission meet)

3) OPTIONAL for ease of access: Remove the air cleaner box from it's mounts and the throttle body-(2) 10mm Bolts, Hoses, Hose Clamp etc.
4) Unplug the white, 2 pin connector by pressing on the locking tang and pulling the two apart (Only 1 terminal occupied)

5) Remove the 12mm mounting bolt (Use ratchet and 8" extension with 12mm socket, I found that putting the ratchet extension down in between the throttle and cruise cables worked best, straight shot)

6) Remove the old sensor
7) Clean the mounting surface on the engine block (Use a scotchbrite pad or sandpaper, this will ensure a good ground)

8) Install the new sensor (Be sure to position the sensor correctly, the sensors harness connector should be facing towards the passenger's side at a 45 degree angle)

9) Install the 12mm mounting bolt (Torque to 17.4 +/- 2.2 ft. lbs. using torque wrench, DO NOT IMPROPERLY TORQUE)

10) Plug in the new sensors wiring connector into the vehicle harness (White, 2 pin connector, be sure the two white connectors firmly click into place)
11) Clear the ECU of DTC's using a Scan Tool or by leaving the battery disconnected for a few minutes
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Old 02-19-2018, 03:36 PM   #2
NASIOC Supporter
Member#: 30669
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT


Nice write up.
Applicable to many Subaru engines.......should be posted in "service".

Low oil pressure will also trip the same code, ask me how I know (a few thousand bucks later.....).
The sensor and circuit is indeed looking for a frequency signature,
This can be poor fuel, weak ignition, piston carbon, loose tools, loose mounting hardware or low oil pressure along with rod or main bearing issues.

If you remove the sensor, look for cracks in it's housing. Sometimes you get a "knock CEL" when damp out, you clean the engine, you drive through deepish water. This shorts the sensor and you trip the same code (been there, done that, more than once).
Common issue when replacing it, you over torque the sensor and crack the housing.
See previous.
Charlie-III is offline   Reply With Quote

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