knock sensor resistance - Subaru Enthusiasts Car Club of the Sierras

Highdesertsuby · 2011-04-23, 05:23 PM

ok, i did my homework and found a post from way back in 07 about testing knock sensors, but no information about the actual specs. Car had been throwing a cel PO0325 off and on for about 2-3 months. I pulled the old sensor off and saw the housing was cracked...bad sensor. Bought a new one, installed it and cleared the code, and now the cel comes on all the time with the same 0325 code. Got out the multimeter and got the following numbers...

1997 Impreza L 2.2
old sensor - no continuity, means it's dead
new sensor - .780 with the meter set to 200k ohms, .000 when set to 2000k ohms
voltage at knock sensor connector - 4.65v with ignition on, but not running

from what i have read, it should read a minimum of 400k ohms for the sensor and at least 2v at the connector. I'm still learning about electrical systems, so I'm not sure what these readings are supposed to be. From what i can figure out, the circuit is getting plenty of volts and signal from the ecu, but the resistance on the sensor seems way low. Can anyone verify this? Thanks in advance.

Highdesertsuby · 2011-04-23, 05:25 PM

also want to double-check on the sensor orientation...is it supposed to be 60 degrees off of center towards the rear or the front of the engine?

Dean · 2011-04-23, 06:02 PM

You sure it is supposed to be 400K ohms or just more than 400 ohms? That looks like 780ohms.

Highdesertsuby · 2011-04-23, 07:04 PM

Quote:

Originally Posted by Dean

You sure it is supposed to be 400K ohms or just more than 400 ohms? That looks like 780ohms.

it was supposed to be 400k ohms minimum. the info supposedly came from a troubleshooting section of a repair maunal (not sure which one...

CHECK KNOCK SENSOR.
1) Disconnect the connector from knock sensor.
2) Measure the resistance between knock
sensor connector terminal and engine ground.
Terminal
No. 2 — Engine ground:
Is the resistance less than
400 kΩ?
Replace the
knock sensor.
<Ref. to FU-31,
Knock Sensor.>
Repair ground
short circuit in
harness between
knock sensor connector
and ECM
connector.

It seems to indicate that a reading higher than 400k ohms was ok. In that case, isn't 780 ohms way less than 400k? (assuming the "k" means multiply by 1,000...or 400,000 ohms in this case). Still not sure, learning this stuff on my own.

Dean · 2011-04-23, 07:26 PM

Yes, 780<1K<400K. Sounds like that knock sensor is failing in the shorted direction rather than open like the old one.

Highdesertsuby · 2011-04-23, 08:49 PM

very likely...it is a new sensor, but I know that doesn't automatically mean it is a good one. I'll pick up another one and see if that fixes the problem.

A1337STI · 2011-04-26, 10:10 AM

I've had new parts fail on me, right out of the box. fuel pump, and i think either a ball joint or a tie rod end (outer) I've also had mis boxed items (not a sensor yet) again fuel pump ... heh

2011-04-23, 05:23 PM	#1
Highdesertsuby EJ22 Join Date: Mar 2008 Location: Reno Posts: 154 Car: 1997 Subaru Impreza L Class: n/a This is going to take crackerjack timing...	knock sensor resistance ok, i did my homework and found a post from way back in 07 about testing knock sensors, but no information about the actual specs. Car had been throwing a cel PO0325 off and on for about 2-3 months. I pulled the old sensor off and saw the housing was cracked...bad sensor. Bought a new one, installed it and cleared the code, and now the cel comes on all the time with the same 0325 code. Got out the multimeter and got the following numbers... 1997 Impreza L 2.2 old sensor - no continuity, means it's dead new sensor - .780 with the meter set to 200k ohms, .000 when set to 2000k ohms voltage at knock sensor connector - 4.65v with ignition on, but not running from what i have read, it should read a minimum of 400k ohms for the sensor and at least 2v at the connector. I'm still learning about electrical systems, so I'm not sure what these readings are supposed to be. From what i can figure out, the circuit is getting plenty of volts and signal from the ecu, but the resistance on the sensor seems way low. Can anyone verify this? Thanks in advance.

2011-04-23, 06:02 PM	#3
Dean Señor Cheap Bastarde Real Name: Dean Join Date: May 2003 Location: $99 Tire Store Posts: 9,294 Car: $.04 STI Class: Fast,Cheap & Reliable=STI Deal, did somebody say Deal? Oh, Dean, yeah that's me.	You sure it is supposed to be 400K ohms or just more than 400 ohms? That looks like 780ohms. __________________ I am a Commodore PET --- Now get off my lawn you kids...

2011-04-23, 07:26 PM	#5
Dean Señor Cheap Bastarde Real Name: Dean Join Date: May 2003 Location: $99 Tire Store Posts: 9,294 Car: $.04 STI Class: Fast,Cheap & Reliable=STI Deal, did somebody say Deal? Oh, Dean, yeah that's me.	Yes, 780<1K<400K. Sounds like that knock sensor is failing in the shorted direction rather than open like the old one. __________________ I am a Commodore PET --- Now get off my lawn you kids...

2011-04-26, 10:10 AM	#7
A1337STI EJ205 Join Date: Jan 2006 Location: Reno, NV Posts: 1,840 Car: Impreza and an Impreza Class: AS / CRS PerfStock "pedal on the right"	I've had new parts fail on me, right out of the box. fuel pump, and i think either a ball joint or a tie rod end (outer) I've also had mis boxed items (not a sensor yet) again fuel pump ... heh __________________ Fighting uphill battles, one bullet at a time!

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2011-04-23, 05:25 PM	#2
Highdesertsuby EJ22 Join Date: Mar 2008 Location: Reno Posts: 154 Car: 1997 Subaru Impreza L Class: n/a This is going to take crackerjack timing...	also want to double-check on the sensor orientation...is it supposed to be 60 degrees off of center towards the rear or the front of the engine?

2011-04-23, 08:49 PM	#6
Highdesertsuby EJ22 Join Date: Mar 2008 Location: Reno Posts: 154 Car: 1997 Subaru Impreza L Class: n/a This is going to take crackerjack timing...	very likely...it is a new sensor, but I know that doesn't automatically mean it is a good one. I'll pick up another one and see if that fixes the problem.