Join Date: Jun 2019
Location: Virginia USA
Car Year: 2005
Car Model: Forrester
Feedback Score: 0 reviews
New Knock Sensor
Sensor is located on top of crankcase behind the air manifold and to the left side.
Test to diagnose:
Open voltage on sensor lead with pigtail disconnected and key switched on: ~5V DC
Voltage with sensor connected is ~ 2.5V DC
New knock sensor readings:
560k ohms DC pigtail to shell ground
Test output by measuring AC millivolts and tap sensor very gently with metal object. You will see the taps on the bar graph of the meter and a small change in voltage reading.
Remove the air plenum to allow access easily.
1 12mm bolt holds it on. Use a swivel joint on an extension with the socket.
Remove the sensor from the crankcase.
Disconnect sensor from harness by pushing down the small catch on the connector.
Angle sensor on crankcase so it seats flat on crankcase and lead is free.
Torque new sensor to 17.4 ft/lbs
Connect pigtail to harness.
Return the air plenum.
I found it easier to start the bolt by using my left hand from the right side of the car.